forked from OSchip/llvm-project
1910 lines
77 KiB
C++
1910 lines
77 KiB
C++
//===- BasicAliasAnalysis.cpp - Stateless Alias Analysis Impl -------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file defines the primary stateless implementation of the
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// Alias Analysis interface that implements identities (two different
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// globals cannot alias, etc), but does no stateful analysis.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Analysis/BasicAliasAnalysis.h"
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#include "llvm/ADT/APInt.h"
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#include "llvm/ADT/SmallPtrSet.h"
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/Analysis/AliasAnalysis.h"
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#include "llvm/Analysis/AssumptionCache.h"
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#include "llvm/Analysis/CFG.h"
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#include "llvm/Analysis/CaptureTracking.h"
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#include "llvm/Analysis/InstructionSimplify.h"
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#include "llvm/Analysis/LoopInfo.h"
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#include "llvm/Analysis/MemoryBuiltins.h"
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#include "llvm/Analysis/MemoryLocation.h"
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#include "llvm/Analysis/TargetLibraryInfo.h"
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#include "llvm/Analysis/ValueTracking.h"
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#include "llvm/IR/Argument.h"
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#include "llvm/IR/Attributes.h"
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#include "llvm/IR/CallSite.h"
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#include "llvm/IR/Constant.h"
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#include "llvm/IR/Constants.h"
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#include "llvm/IR/DataLayout.h"
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#include "llvm/IR/DerivedTypes.h"
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#include "llvm/IR/Dominators.h"
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#include "llvm/IR/Function.h"
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#include "llvm/IR/GetElementPtrTypeIterator.h"
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#include "llvm/IR/GlobalAlias.h"
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#include "llvm/IR/GlobalVariable.h"
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#include "llvm/IR/InstrTypes.h"
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#include "llvm/IR/Instruction.h"
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#include "llvm/IR/Instructions.h"
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#include "llvm/IR/IntrinsicInst.h"
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#include "llvm/IR/Intrinsics.h"
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#include "llvm/IR/Metadata.h"
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#include "llvm/IR/Operator.h"
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#include "llvm/IR/Type.h"
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#include "llvm/IR/User.h"
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#include "llvm/IR/Value.h"
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#include "llvm/Pass.h"
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#include "llvm/Support/Casting.h"
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#include "llvm/Support/CommandLine.h"
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#include "llvm/Support/Compiler.h"
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#include "llvm/Support/KnownBits.h"
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#include <cassert>
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#include <cstdint>
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#include <cstdlib>
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#include <utility>
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#define DEBUG_TYPE "basicaa"
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using namespace llvm;
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/// Enable analysis of recursive PHI nodes.
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static cl::opt<bool> EnableRecPhiAnalysis("basicaa-recphi", cl::Hidden,
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cl::init(false));
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/// SearchLimitReached / SearchTimes shows how often the limit of
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/// to decompose GEPs is reached. It will affect the precision
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/// of basic alias analysis.
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STATISTIC(SearchLimitReached, "Number of times the limit to "
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"decompose GEPs is reached");
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STATISTIC(SearchTimes, "Number of times a GEP is decomposed");
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/// Cutoff after which to stop analysing a set of phi nodes potentially involved
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/// in a cycle. Because we are analysing 'through' phi nodes, we need to be
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/// careful with value equivalence. We use reachability to make sure a value
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/// cannot be involved in a cycle.
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const unsigned MaxNumPhiBBsValueReachabilityCheck = 20;
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// The max limit of the search depth in DecomposeGEPExpression() and
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// GetUnderlyingObject(), both functions need to use the same search
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// depth otherwise the algorithm in aliasGEP will assert.
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static const unsigned MaxLookupSearchDepth = 6;
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bool BasicAAResult::invalidate(Function &F, const PreservedAnalyses &PA,
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FunctionAnalysisManager::Invalidator &Inv) {
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// We don't care if this analysis itself is preserved, it has no state. But
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// we need to check that the analyses it depends on have been. Note that we
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// may be created without handles to some analyses and in that case don't
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// depend on them.
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if (Inv.invalidate<AssumptionAnalysis>(F, PA) ||
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(DT && Inv.invalidate<DominatorTreeAnalysis>(F, PA)) ||
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(LI && Inv.invalidate<LoopAnalysis>(F, PA)))
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return true;
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// Otherwise this analysis result remains valid.
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return false;
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}
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//===----------------------------------------------------------------------===//
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// Useful predicates
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//===----------------------------------------------------------------------===//
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/// Returns true if the pointer is to a function-local object that never
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/// escapes from the function.
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static bool isNonEscapingLocalObject(const Value *V) {
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// If this is a local allocation, check to see if it escapes.
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if (isa<AllocaInst>(V) || isNoAliasCall(V))
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// Set StoreCaptures to True so that we can assume in our callers that the
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// pointer is not the result of a load instruction. Currently
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// PointerMayBeCaptured doesn't have any special analysis for the
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// StoreCaptures=false case; if it did, our callers could be refined to be
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// more precise.
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return !PointerMayBeCaptured(V, false, /*StoreCaptures=*/true);
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// If this is an argument that corresponds to a byval or noalias argument,
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// then it has not escaped before entering the function. Check if it escapes
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// inside the function.
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if (const Argument *A = dyn_cast<Argument>(V))
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if (A->hasByValAttr() || A->hasNoAliasAttr())
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// Note even if the argument is marked nocapture, we still need to check
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// for copies made inside the function. The nocapture attribute only
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// specifies that there are no copies made that outlive the function.
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return !PointerMayBeCaptured(V, false, /*StoreCaptures=*/true);
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return false;
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}
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/// Returns true if the pointer is one which would have been considered an
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/// escape by isNonEscapingLocalObject.
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static bool isEscapeSource(const Value *V) {
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if (isa<CallInst>(V) || isa<InvokeInst>(V) || isa<Argument>(V))
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return true;
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// The load case works because isNonEscapingLocalObject considers all
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// stores to be escapes (it passes true for the StoreCaptures argument
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// to PointerMayBeCaptured).
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if (isa<LoadInst>(V))
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return true;
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return false;
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}
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/// Returns the size of the object specified by V or UnknownSize if unknown.
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static uint64_t getObjectSize(const Value *V, const DataLayout &DL,
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const TargetLibraryInfo &TLI,
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bool RoundToAlign = false) {
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uint64_t Size;
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ObjectSizeOpts Opts;
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Opts.RoundToAlign = RoundToAlign;
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if (getObjectSize(V, Size, DL, &TLI, Opts))
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return Size;
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return MemoryLocation::UnknownSize;
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}
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/// Returns true if we can prove that the object specified by V is smaller than
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/// Size.
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static bool isObjectSmallerThan(const Value *V, uint64_t Size,
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const DataLayout &DL,
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const TargetLibraryInfo &TLI) {
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// Note that the meanings of the "object" are slightly different in the
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// following contexts:
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// c1: llvm::getObjectSize()
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// c2: llvm.objectsize() intrinsic
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// c3: isObjectSmallerThan()
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// c1 and c2 share the same meaning; however, the meaning of "object" in c3
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// refers to the "entire object".
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//
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// Consider this example:
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// char *p = (char*)malloc(100)
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// char *q = p+80;
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//
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// In the context of c1 and c2, the "object" pointed by q refers to the
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// stretch of memory of q[0:19]. So, getObjectSize(q) should return 20.
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//
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// However, in the context of c3, the "object" refers to the chunk of memory
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// being allocated. So, the "object" has 100 bytes, and q points to the middle
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// the "object". In case q is passed to isObjectSmallerThan() as the 1st
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// parameter, before the llvm::getObjectSize() is called to get the size of
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// entire object, we should:
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// - either rewind the pointer q to the base-address of the object in
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// question (in this case rewind to p), or
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// - just give up. It is up to caller to make sure the pointer is pointing
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// to the base address the object.
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//
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// We go for 2nd option for simplicity.
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if (!isIdentifiedObject(V))
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return false;
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// This function needs to use the aligned object size because we allow
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// reads a bit past the end given sufficient alignment.
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uint64_t ObjectSize = getObjectSize(V, DL, TLI, /*RoundToAlign*/ true);
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return ObjectSize != MemoryLocation::UnknownSize && ObjectSize < Size;
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}
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/// Returns true if we can prove that the object specified by V has size Size.
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static bool isObjectSize(const Value *V, uint64_t Size, const DataLayout &DL,
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const TargetLibraryInfo &TLI) {
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uint64_t ObjectSize = getObjectSize(V, DL, TLI);
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return ObjectSize != MemoryLocation::UnknownSize && ObjectSize == Size;
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}
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//===----------------------------------------------------------------------===//
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// GetElementPtr Instruction Decomposition and Analysis
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//===----------------------------------------------------------------------===//
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/// Analyzes the specified value as a linear expression: "A*V + B", where A and
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/// B are constant integers.
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///
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/// Returns the scale and offset values as APInts and return V as a Value*, and
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/// return whether we looked through any sign or zero extends. The incoming
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/// Value is known to have IntegerType, and it may already be sign or zero
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/// extended.
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///
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/// Note that this looks through extends, so the high bits may not be
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/// represented in the result.
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/*static*/ const Value *BasicAAResult::GetLinearExpression(
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const Value *V, APInt &Scale, APInt &Offset, unsigned &ZExtBits,
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unsigned &SExtBits, const DataLayout &DL, unsigned Depth,
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AssumptionCache *AC, DominatorTree *DT, bool &NSW, bool &NUW) {
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assert(V->getType()->isIntegerTy() && "Not an integer value");
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// Limit our recursion depth.
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if (Depth == 6) {
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Scale = 1;
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Offset = 0;
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return V;
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}
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if (const ConstantInt *Const = dyn_cast<ConstantInt>(V)) {
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// If it's a constant, just convert it to an offset and remove the variable.
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// If we've been called recursively, the Offset bit width will be greater
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// than the constant's (the Offset's always as wide as the outermost call),
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// so we'll zext here and process any extension in the isa<SExtInst> &
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// isa<ZExtInst> cases below.
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Offset += Const->getValue().zextOrSelf(Offset.getBitWidth());
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assert(Scale == 0 && "Constant values don't have a scale");
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return V;
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}
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if (const BinaryOperator *BOp = dyn_cast<BinaryOperator>(V)) {
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if (ConstantInt *RHSC = dyn_cast<ConstantInt>(BOp->getOperand(1))) {
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// If we've been called recursively, then Offset and Scale will be wider
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// than the BOp operands. We'll always zext it here as we'll process sign
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// extensions below (see the isa<SExtInst> / isa<ZExtInst> cases).
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APInt RHS = RHSC->getValue().zextOrSelf(Offset.getBitWidth());
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switch (BOp->getOpcode()) {
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default:
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// We don't understand this instruction, so we can't decompose it any
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// further.
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Scale = 1;
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Offset = 0;
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return V;
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case Instruction::Or:
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// X|C == X+C if all the bits in C are unset in X. Otherwise we can't
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// analyze it.
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if (!MaskedValueIsZero(BOp->getOperand(0), RHSC->getValue(), DL, 0, AC,
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BOp, DT)) {
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Scale = 1;
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Offset = 0;
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return V;
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}
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LLVM_FALLTHROUGH;
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case Instruction::Add:
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V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, ZExtBits,
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SExtBits, DL, Depth + 1, AC, DT, NSW, NUW);
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Offset += RHS;
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break;
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case Instruction::Sub:
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V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, ZExtBits,
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SExtBits, DL, Depth + 1, AC, DT, NSW, NUW);
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Offset -= RHS;
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break;
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case Instruction::Mul:
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V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, ZExtBits,
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SExtBits, DL, Depth + 1, AC, DT, NSW, NUW);
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Offset *= RHS;
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Scale *= RHS;
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break;
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case Instruction::Shl:
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V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, ZExtBits,
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SExtBits, DL, Depth + 1, AC, DT, NSW, NUW);
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// We're trying to linearize an expression of the kind:
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// shl i8 -128, 36
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// where the shift count exceeds the bitwidth of the type.
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// We can't decompose this further (the expression would return
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// a poison value).
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if (Offset.getBitWidth() < RHS.getLimitedValue() ||
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Scale.getBitWidth() < RHS.getLimitedValue()) {
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Scale = 1;
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Offset = 0;
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return V;
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}
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Offset <<= RHS.getLimitedValue();
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Scale <<= RHS.getLimitedValue();
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// the semantics of nsw and nuw for left shifts don't match those of
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// multiplications, so we won't propagate them.
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NSW = NUW = false;
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return V;
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}
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if (isa<OverflowingBinaryOperator>(BOp)) {
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NUW &= BOp->hasNoUnsignedWrap();
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NSW &= BOp->hasNoSignedWrap();
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}
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return V;
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}
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}
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// Since GEP indices are sign extended anyway, we don't care about the high
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// bits of a sign or zero extended value - just scales and offsets. The
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// extensions have to be consistent though.
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if (isa<SExtInst>(V) || isa<ZExtInst>(V)) {
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Value *CastOp = cast<CastInst>(V)->getOperand(0);
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unsigned NewWidth = V->getType()->getPrimitiveSizeInBits();
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unsigned SmallWidth = CastOp->getType()->getPrimitiveSizeInBits();
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unsigned OldZExtBits = ZExtBits, OldSExtBits = SExtBits;
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const Value *Result =
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GetLinearExpression(CastOp, Scale, Offset, ZExtBits, SExtBits, DL,
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Depth + 1, AC, DT, NSW, NUW);
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// zext(zext(%x)) == zext(%x), and similarly for sext; we'll handle this
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// by just incrementing the number of bits we've extended by.
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unsigned ExtendedBy = NewWidth - SmallWidth;
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if (isa<SExtInst>(V) && ZExtBits == 0) {
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// sext(sext(%x, a), b) == sext(%x, a + b)
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if (NSW) {
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// We haven't sign-wrapped, so it's valid to decompose sext(%x + c)
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// into sext(%x) + sext(c). We'll sext the Offset ourselves:
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unsigned OldWidth = Offset.getBitWidth();
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Offset = Offset.trunc(SmallWidth).sext(NewWidth).zextOrSelf(OldWidth);
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} else {
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// We may have signed-wrapped, so don't decompose sext(%x + c) into
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// sext(%x) + sext(c)
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Scale = 1;
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Offset = 0;
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Result = CastOp;
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ZExtBits = OldZExtBits;
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SExtBits = OldSExtBits;
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}
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SExtBits += ExtendedBy;
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} else {
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// sext(zext(%x, a), b) = zext(zext(%x, a), b) = zext(%x, a + b)
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if (!NUW) {
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// We may have unsigned-wrapped, so don't decompose zext(%x + c) into
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// zext(%x) + zext(c)
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Scale = 1;
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Offset = 0;
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Result = CastOp;
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ZExtBits = OldZExtBits;
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SExtBits = OldSExtBits;
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}
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ZExtBits += ExtendedBy;
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}
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return Result;
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}
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Scale = 1;
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Offset = 0;
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return V;
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}
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/// To ensure a pointer offset fits in an integer of size PointerSize
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/// (in bits) when that size is smaller than 64. This is an issue in
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/// particular for 32b programs with negative indices that rely on two's
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/// complement wrap-arounds for precise alias information.
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static int64_t adjustToPointerSize(int64_t Offset, unsigned PointerSize) {
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assert(PointerSize <= 64 && "Invalid PointerSize!");
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unsigned ShiftBits = 64 - PointerSize;
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return (int64_t)((uint64_t)Offset << ShiftBits) >> ShiftBits;
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}
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/// If V is a symbolic pointer expression, decompose it into a base pointer
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/// with a constant offset and a number of scaled symbolic offsets.
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///
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/// The scaled symbolic offsets (represented by pairs of a Value* and a scale
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/// in the VarIndices vector) are Value*'s that are known to be scaled by the
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/// specified amount, but which may have other unrepresented high bits. As
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/// such, the gep cannot necessarily be reconstructed from its decomposed form.
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///
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/// When DataLayout is around, this function is capable of analyzing everything
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/// that GetUnderlyingObject can look through. To be able to do that
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/// GetUnderlyingObject and DecomposeGEPExpression must use the same search
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/// depth (MaxLookupSearchDepth). When DataLayout not is around, it just looks
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/// through pointer casts.
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bool BasicAAResult::DecomposeGEPExpression(const Value *V,
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DecomposedGEP &Decomposed, const DataLayout &DL, AssumptionCache *AC,
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DominatorTree *DT) {
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// Limit recursion depth to limit compile time in crazy cases.
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unsigned MaxLookup = MaxLookupSearchDepth;
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SearchTimes++;
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Decomposed.StructOffset = 0;
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Decomposed.OtherOffset = 0;
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Decomposed.VarIndices.clear();
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do {
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// See if this is a bitcast or GEP.
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const Operator *Op = dyn_cast<Operator>(V);
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if (!Op) {
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// The only non-operator case we can handle are GlobalAliases.
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if (const GlobalAlias *GA = dyn_cast<GlobalAlias>(V)) {
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if (!GA->isInterposable()) {
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V = GA->getAliasee();
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continue;
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}
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}
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Decomposed.Base = V;
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return false;
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}
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if (Op->getOpcode() == Instruction::BitCast ||
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Op->getOpcode() == Instruction::AddrSpaceCast) {
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V = Op->getOperand(0);
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continue;
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}
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const GEPOperator *GEPOp = dyn_cast<GEPOperator>(Op);
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if (!GEPOp) {
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if (auto CS = ImmutableCallSite(V))
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if (const Value *RV = CS.getReturnedArgOperand()) {
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V = RV;
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continue;
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}
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// If it's not a GEP, hand it off to SimplifyInstruction to see if it
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// can come up with something. This matches what GetUnderlyingObject does.
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if (const Instruction *I = dyn_cast<Instruction>(V))
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// TODO: Get a DominatorTree and AssumptionCache and use them here
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// (these are both now available in this function, but this should be
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// updated when GetUnderlyingObject is updated). TLI should be
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// provided also.
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if (const Value *Simplified =
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SimplifyInstruction(const_cast<Instruction *>(I), DL)) {
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V = Simplified;
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continue;
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}
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Decomposed.Base = V;
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return false;
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}
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// Don't attempt to analyze GEPs over unsized objects.
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if (!GEPOp->getSourceElementType()->isSized()) {
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Decomposed.Base = V;
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return false;
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}
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unsigned AS = GEPOp->getPointerAddressSpace();
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// Walk the indices of the GEP, accumulating them into BaseOff/VarIndices.
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gep_type_iterator GTI = gep_type_begin(GEPOp);
|
|
unsigned PointerSize = DL.getPointerSizeInBits(AS);
|
|
// Assume all GEP operands are constants until proven otherwise.
|
|
bool GepHasConstantOffset = true;
|
|
for (User::const_op_iterator I = GEPOp->op_begin() + 1, E = GEPOp->op_end();
|
|
I != E; ++I, ++GTI) {
|
|
const Value *Index = *I;
|
|
// Compute the (potentially symbolic) offset in bytes for this index.
|
|
if (StructType *STy = GTI.getStructTypeOrNull()) {
|
|
// For a struct, add the member offset.
|
|
unsigned FieldNo = cast<ConstantInt>(Index)->getZExtValue();
|
|
if (FieldNo == 0)
|
|
continue;
|
|
|
|
Decomposed.StructOffset +=
|
|
DL.getStructLayout(STy)->getElementOffset(FieldNo);
|
|
continue;
|
|
}
|
|
|
|
// For an array/pointer, add the element offset, explicitly scaled.
|
|
if (const ConstantInt *CIdx = dyn_cast<ConstantInt>(Index)) {
|
|
if (CIdx->isZero())
|
|
continue;
|
|
Decomposed.OtherOffset +=
|
|
DL.getTypeAllocSize(GTI.getIndexedType()) * CIdx->getSExtValue();
|
|
continue;
|
|
}
|
|
|
|
GepHasConstantOffset = false;
|
|
|
|
uint64_t Scale = DL.getTypeAllocSize(GTI.getIndexedType());
|
|
unsigned ZExtBits = 0, SExtBits = 0;
|
|
|
|
// If the integer type is smaller than the pointer size, it is implicitly
|
|
// sign extended to pointer size.
|
|
unsigned Width = Index->getType()->getIntegerBitWidth();
|
|
if (PointerSize > Width)
|
|
SExtBits += PointerSize - Width;
|
|
|
|
// Use GetLinearExpression to decompose the index into a C1*V+C2 form.
|
|
APInt IndexScale(Width, 0), IndexOffset(Width, 0);
|
|
bool NSW = true, NUW = true;
|
|
Index = GetLinearExpression(Index, IndexScale, IndexOffset, ZExtBits,
|
|
SExtBits, DL, 0, AC, DT, NSW, NUW);
|
|
|
|
// All GEP math happens in the width of the pointer type,
|
|
// so we can truncate the value to 64-bits as we don't handle
|
|
// currently pointers larger than 64 bits and we would crash
|
|
// later. TODO: Make `Scale` an APInt to avoid this problem.
|
|
if (IndexScale.getBitWidth() > 64)
|
|
IndexScale = IndexScale.sextOrTrunc(64);
|
|
|
|
// The GEP index scale ("Scale") scales C1*V+C2, yielding (C1*V+C2)*Scale.
|
|
// This gives us an aggregate computation of (C1*Scale)*V + C2*Scale.
|
|
Decomposed.OtherOffset += IndexOffset.getSExtValue() * Scale;
|
|
Scale *= IndexScale.getSExtValue();
|
|
|
|
// If we already had an occurrence of this index variable, merge this
|
|
// scale into it. For example, we want to handle:
|
|
// A[x][x] -> x*16 + x*4 -> x*20
|
|
// This also ensures that 'x' only appears in the index list once.
|
|
for (unsigned i = 0, e = Decomposed.VarIndices.size(); i != e; ++i) {
|
|
if (Decomposed.VarIndices[i].V == Index &&
|
|
Decomposed.VarIndices[i].ZExtBits == ZExtBits &&
|
|
Decomposed.VarIndices[i].SExtBits == SExtBits) {
|
|
Scale += Decomposed.VarIndices[i].Scale;
|
|
Decomposed.VarIndices.erase(Decomposed.VarIndices.begin() + i);
|
|
break;
|
|
}
|
|
}
|
|
|
|
// Make sure that we have a scale that makes sense for this target's
|
|
// pointer size.
|
|
Scale = adjustToPointerSize(Scale, PointerSize);
|
|
|
|
if (Scale) {
|
|
VariableGEPIndex Entry = {Index, ZExtBits, SExtBits,
|
|
static_cast<int64_t>(Scale)};
|
|
Decomposed.VarIndices.push_back(Entry);
|
|
}
|
|
}
|
|
|
|
// Take care of wrap-arounds
|
|
if (GepHasConstantOffset) {
|
|
Decomposed.StructOffset =
|
|
adjustToPointerSize(Decomposed.StructOffset, PointerSize);
|
|
Decomposed.OtherOffset =
|
|
adjustToPointerSize(Decomposed.OtherOffset, PointerSize);
|
|
}
|
|
|
|
// Analyze the base pointer next.
|
|
V = GEPOp->getOperand(0);
|
|
} while (--MaxLookup);
|
|
|
|
// If the chain of expressions is too deep, just return early.
|
|
Decomposed.Base = V;
|
|
SearchLimitReached++;
|
|
return true;
|
|
}
|
|
|
|
/// Returns whether the given pointer value points to memory that is local to
|
|
/// the function, with global constants being considered local to all
|
|
/// functions.
|
|
bool BasicAAResult::pointsToConstantMemory(const MemoryLocation &Loc,
|
|
bool OrLocal) {
|
|
assert(Visited.empty() && "Visited must be cleared after use!");
|
|
|
|
unsigned MaxLookup = 8;
|
|
SmallVector<const Value *, 16> Worklist;
|
|
Worklist.push_back(Loc.Ptr);
|
|
do {
|
|
const Value *V = GetUnderlyingObject(Worklist.pop_back_val(), DL);
|
|
if (!Visited.insert(V).second) {
|
|
Visited.clear();
|
|
return AAResultBase::pointsToConstantMemory(Loc, OrLocal);
|
|
}
|
|
|
|
// An alloca instruction defines local memory.
|
|
if (OrLocal && isa<AllocaInst>(V))
|
|
continue;
|
|
|
|
// A global constant counts as local memory for our purposes.
|
|
if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V)) {
|
|
// Note: this doesn't require GV to be "ODR" because it isn't legal for a
|
|
// global to be marked constant in some modules and non-constant in
|
|
// others. GV may even be a declaration, not a definition.
|
|
if (!GV->isConstant()) {
|
|
Visited.clear();
|
|
return AAResultBase::pointsToConstantMemory(Loc, OrLocal);
|
|
}
|
|
continue;
|
|
}
|
|
|
|
// If both select values point to local memory, then so does the select.
|
|
if (const SelectInst *SI = dyn_cast<SelectInst>(V)) {
|
|
Worklist.push_back(SI->getTrueValue());
|
|
Worklist.push_back(SI->getFalseValue());
|
|
continue;
|
|
}
|
|
|
|
// If all values incoming to a phi node point to local memory, then so does
|
|
// the phi.
|
|
if (const PHINode *PN = dyn_cast<PHINode>(V)) {
|
|
// Don't bother inspecting phi nodes with many operands.
|
|
if (PN->getNumIncomingValues() > MaxLookup) {
|
|
Visited.clear();
|
|
return AAResultBase::pointsToConstantMemory(Loc, OrLocal);
|
|
}
|
|
for (Value *IncValue : PN->incoming_values())
|
|
Worklist.push_back(IncValue);
|
|
continue;
|
|
}
|
|
|
|
// Otherwise be conservative.
|
|
Visited.clear();
|
|
return AAResultBase::pointsToConstantMemory(Loc, OrLocal);
|
|
} while (!Worklist.empty() && --MaxLookup);
|
|
|
|
Visited.clear();
|
|
return Worklist.empty();
|
|
}
|
|
|
|
/// Returns the behavior when calling the given call site.
|
|
FunctionModRefBehavior BasicAAResult::getModRefBehavior(ImmutableCallSite CS) {
|
|
if (CS.doesNotAccessMemory())
|
|
// Can't do better than this.
|
|
return FMRB_DoesNotAccessMemory;
|
|
|
|
FunctionModRefBehavior Min = FMRB_UnknownModRefBehavior;
|
|
|
|
// If the callsite knows it only reads memory, don't return worse
|
|
// than that.
|
|
if (CS.onlyReadsMemory())
|
|
Min = FMRB_OnlyReadsMemory;
|
|
else if (CS.doesNotReadMemory())
|
|
Min = FMRB_DoesNotReadMemory;
|
|
|
|
if (CS.onlyAccessesArgMemory())
|
|
Min = FunctionModRefBehavior(Min & FMRB_OnlyAccessesArgumentPointees);
|
|
else if (CS.onlyAccessesInaccessibleMemory())
|
|
Min = FunctionModRefBehavior(Min & FMRB_OnlyAccessesInaccessibleMem);
|
|
else if (CS.onlyAccessesInaccessibleMemOrArgMem())
|
|
Min = FunctionModRefBehavior(Min & FMRB_OnlyAccessesInaccessibleOrArgMem);
|
|
|
|
// If CS has operand bundles then aliasing attributes from the function it
|
|
// calls do not directly apply to the CallSite. This can be made more
|
|
// precise in the future.
|
|
if (!CS.hasOperandBundles())
|
|
if (const Function *F = CS.getCalledFunction())
|
|
Min =
|
|
FunctionModRefBehavior(Min & getBestAAResults().getModRefBehavior(F));
|
|
|
|
return Min;
|
|
}
|
|
|
|
/// Returns the behavior when calling the given function. For use when the call
|
|
/// site is not known.
|
|
FunctionModRefBehavior BasicAAResult::getModRefBehavior(const Function *F) {
|
|
// If the function declares it doesn't access memory, we can't do better.
|
|
if (F->doesNotAccessMemory())
|
|
return FMRB_DoesNotAccessMemory;
|
|
|
|
FunctionModRefBehavior Min = FMRB_UnknownModRefBehavior;
|
|
|
|
// If the function declares it only reads memory, go with that.
|
|
if (F->onlyReadsMemory())
|
|
Min = FMRB_OnlyReadsMemory;
|
|
else if (F->doesNotReadMemory())
|
|
Min = FMRB_DoesNotReadMemory;
|
|
|
|
if (F->onlyAccessesArgMemory())
|
|
Min = FunctionModRefBehavior(Min & FMRB_OnlyAccessesArgumentPointees);
|
|
else if (F->onlyAccessesInaccessibleMemory())
|
|
Min = FunctionModRefBehavior(Min & FMRB_OnlyAccessesInaccessibleMem);
|
|
else if (F->onlyAccessesInaccessibleMemOrArgMem())
|
|
Min = FunctionModRefBehavior(Min & FMRB_OnlyAccessesInaccessibleOrArgMem);
|
|
|
|
return Min;
|
|
}
|
|
|
|
/// Returns true if this is a writeonly (i.e Mod only) parameter.
|
|
static bool isWriteOnlyParam(ImmutableCallSite CS, unsigned ArgIdx,
|
|
const TargetLibraryInfo &TLI) {
|
|
if (CS.paramHasAttr(ArgIdx, Attribute::WriteOnly))
|
|
return true;
|
|
|
|
// We can bound the aliasing properties of memset_pattern16 just as we can
|
|
// for memcpy/memset. This is particularly important because the
|
|
// LoopIdiomRecognizer likes to turn loops into calls to memset_pattern16
|
|
// whenever possible.
|
|
// FIXME Consider handling this in InferFunctionAttr.cpp together with other
|
|
// attributes.
|
|
LibFunc F;
|
|
if (CS.getCalledFunction() && TLI.getLibFunc(*CS.getCalledFunction(), F) &&
|
|
F == LibFunc_memset_pattern16 && TLI.has(F))
|
|
if (ArgIdx == 0)
|
|
return true;
|
|
|
|
// TODO: memset_pattern4, memset_pattern8
|
|
// TODO: _chk variants
|
|
// TODO: strcmp, strcpy
|
|
|
|
return false;
|
|
}
|
|
|
|
ModRefInfo BasicAAResult::getArgModRefInfo(ImmutableCallSite CS,
|
|
unsigned ArgIdx) {
|
|
// Checking for known builtin intrinsics and target library functions.
|
|
if (isWriteOnlyParam(CS, ArgIdx, TLI))
|
|
return ModRefInfo::Mod;
|
|
|
|
if (CS.paramHasAttr(ArgIdx, Attribute::ReadOnly))
|
|
return ModRefInfo::Ref;
|
|
|
|
if (CS.paramHasAttr(ArgIdx, Attribute::ReadNone))
|
|
return ModRefInfo::NoModRef;
|
|
|
|
return AAResultBase::getArgModRefInfo(CS, ArgIdx);
|
|
}
|
|
|
|
static bool isIntrinsicCall(ImmutableCallSite CS, Intrinsic::ID IID) {
|
|
const IntrinsicInst *II = dyn_cast<IntrinsicInst>(CS.getInstruction());
|
|
return II && II->getIntrinsicID() == IID;
|
|
}
|
|
|
|
#ifndef NDEBUG
|
|
static const Function *getParent(const Value *V) {
|
|
if (const Instruction *inst = dyn_cast<Instruction>(V)) {
|
|
if (!inst->getParent())
|
|
return nullptr;
|
|
return inst->getParent()->getParent();
|
|
}
|
|
|
|
if (const Argument *arg = dyn_cast<Argument>(V))
|
|
return arg->getParent();
|
|
|
|
return nullptr;
|
|
}
|
|
|
|
static bool notDifferentParent(const Value *O1, const Value *O2) {
|
|
|
|
const Function *F1 = getParent(O1);
|
|
const Function *F2 = getParent(O2);
|
|
|
|
return !F1 || !F2 || F1 == F2;
|
|
}
|
|
#endif
|
|
|
|
AliasResult BasicAAResult::alias(const MemoryLocation &LocA,
|
|
const MemoryLocation &LocB) {
|
|
assert(notDifferentParent(LocA.Ptr, LocB.Ptr) &&
|
|
"BasicAliasAnalysis doesn't support interprocedural queries.");
|
|
|
|
// If we have a directly cached entry for these locations, we have recursed
|
|
// through this once, so just return the cached results. Notably, when this
|
|
// happens, we don't clear the cache.
|
|
auto CacheIt = AliasCache.find(LocPair(LocA, LocB));
|
|
if (CacheIt != AliasCache.end())
|
|
return CacheIt->second;
|
|
|
|
AliasResult Alias = aliasCheck(LocA.Ptr, LocA.Size, LocA.AATags, LocB.Ptr,
|
|
LocB.Size, LocB.AATags);
|
|
// AliasCache rarely has more than 1 or 2 elements, always use
|
|
// shrink_and_clear so it quickly returns to the inline capacity of the
|
|
// SmallDenseMap if it ever grows larger.
|
|
// FIXME: This should really be shrink_to_inline_capacity_and_clear().
|
|
AliasCache.shrink_and_clear();
|
|
VisitedPhiBBs.clear();
|
|
return Alias;
|
|
}
|
|
|
|
/// Checks to see if the specified callsite can clobber the specified memory
|
|
/// object.
|
|
///
|
|
/// Since we only look at local properties of this function, we really can't
|
|
/// say much about this query. We do, however, use simple "address taken"
|
|
/// analysis on local objects.
|
|
ModRefInfo BasicAAResult::getModRefInfo(ImmutableCallSite CS,
|
|
const MemoryLocation &Loc) {
|
|
assert(notDifferentParent(CS.getInstruction(), Loc.Ptr) &&
|
|
"AliasAnalysis query involving multiple functions!");
|
|
|
|
const Value *Object = GetUnderlyingObject(Loc.Ptr, DL);
|
|
|
|
// If this is a tail call and Loc.Ptr points to a stack location, we know that
|
|
// the tail call cannot access or modify the local stack.
|
|
// We cannot exclude byval arguments here; these belong to the caller of
|
|
// the current function not to the current function, and a tail callee
|
|
// may reference them.
|
|
if (isa<AllocaInst>(Object))
|
|
if (const CallInst *CI = dyn_cast<CallInst>(CS.getInstruction()))
|
|
if (CI->isTailCall())
|
|
return ModRefInfo::NoModRef;
|
|
|
|
// If the pointer is to a locally allocated object that does not escape,
|
|
// then the call can not mod/ref the pointer unless the call takes the pointer
|
|
// as an argument, and itself doesn't capture it.
|
|
if (!isa<Constant>(Object) && CS.getInstruction() != Object &&
|
|
isNonEscapingLocalObject(Object)) {
|
|
|
|
// Optimistically assume that call doesn't touch Object and check this
|
|
// assumption in the following loop.
|
|
ModRefInfo Result = ModRefInfo::NoModRef;
|
|
bool IsMustAlias = true;
|
|
|
|
unsigned OperandNo = 0;
|
|
for (auto CI = CS.data_operands_begin(), CE = CS.data_operands_end();
|
|
CI != CE; ++CI, ++OperandNo) {
|
|
// Only look at the no-capture or byval pointer arguments. If this
|
|
// pointer were passed to arguments that were neither of these, then it
|
|
// couldn't be no-capture.
|
|
if (!(*CI)->getType()->isPointerTy() ||
|
|
(!CS.doesNotCapture(OperandNo) &&
|
|
OperandNo < CS.getNumArgOperands() && !CS.isByValArgument(OperandNo)))
|
|
continue;
|
|
|
|
// Call doesn't access memory through this operand, so we don't care
|
|
// if it aliases with Object.
|
|
if (CS.doesNotAccessMemory(OperandNo))
|
|
continue;
|
|
|
|
// If this is a no-capture pointer argument, see if we can tell that it
|
|
// is impossible to alias the pointer we're checking.
|
|
AliasResult AR =
|
|
getBestAAResults().alias(MemoryLocation(*CI), MemoryLocation(Object));
|
|
if (AR != MustAlias)
|
|
IsMustAlias = false;
|
|
// Operand doesnt alias 'Object', continue looking for other aliases
|
|
if (AR == NoAlias)
|
|
continue;
|
|
// Operand aliases 'Object', but call doesn't modify it. Strengthen
|
|
// initial assumption and keep looking in case if there are more aliases.
|
|
if (CS.onlyReadsMemory(OperandNo)) {
|
|
Result = setRef(Result);
|
|
continue;
|
|
}
|
|
// Operand aliases 'Object' but call only writes into it.
|
|
if (CS.doesNotReadMemory(OperandNo)) {
|
|
Result = setMod(Result);
|
|
continue;
|
|
}
|
|
// This operand aliases 'Object' and call reads and writes into it.
|
|
// Setting ModRef will not yield an early return below, MustAlias is not
|
|
// used further.
|
|
Result = ModRefInfo::ModRef;
|
|
break;
|
|
}
|
|
|
|
// No operand aliases, reset Must bit. Add below if at least one aliases
|
|
// and all aliases found are MustAlias.
|
|
if (isNoModRef(Result))
|
|
IsMustAlias = false;
|
|
|
|
// Early return if we improved mod ref information
|
|
if (!isModAndRefSet(Result)) {
|
|
if (isNoModRef(Result))
|
|
return ModRefInfo::NoModRef;
|
|
return IsMustAlias ? setMust(Result) : clearMust(Result);
|
|
}
|
|
}
|
|
|
|
// If the CallSite is to malloc or calloc, we can assume that it doesn't
|
|
// modify any IR visible value. This is only valid because we assume these
|
|
// routines do not read values visible in the IR. TODO: Consider special
|
|
// casing realloc and strdup routines which access only their arguments as
|
|
// well. Or alternatively, replace all of this with inaccessiblememonly once
|
|
// that's implemented fully.
|
|
auto *Inst = CS.getInstruction();
|
|
if (isMallocOrCallocLikeFn(Inst, &TLI)) {
|
|
// Be conservative if the accessed pointer may alias the allocation -
|
|
// fallback to the generic handling below.
|
|
if (getBestAAResults().alias(MemoryLocation(Inst), Loc) == NoAlias)
|
|
return ModRefInfo::NoModRef;
|
|
}
|
|
|
|
// The semantics of memcpy intrinsics forbid overlap between their respective
|
|
// operands, i.e., source and destination of any given memcpy must no-alias.
|
|
// If Loc must-aliases either one of these two locations, then it necessarily
|
|
// no-aliases the other.
|
|
if (auto *Inst = dyn_cast<MemCpyInst>(CS.getInstruction())) {
|
|
AliasResult SrcAA, DestAA;
|
|
|
|
if ((SrcAA = getBestAAResults().alias(MemoryLocation::getForSource(Inst),
|
|
Loc)) == MustAlias)
|
|
// Loc is exactly the memcpy source thus disjoint from memcpy dest.
|
|
return ModRefInfo::Ref;
|
|
if ((DestAA = getBestAAResults().alias(MemoryLocation::getForDest(Inst),
|
|
Loc)) == MustAlias)
|
|
// The converse case.
|
|
return ModRefInfo::Mod;
|
|
|
|
// It's also possible for Loc to alias both src and dest, or neither.
|
|
ModRefInfo rv = ModRefInfo::NoModRef;
|
|
if (SrcAA != NoAlias)
|
|
rv = setRef(rv);
|
|
if (DestAA != NoAlias)
|
|
rv = setMod(rv);
|
|
return rv;
|
|
}
|
|
|
|
// While the assume intrinsic is marked as arbitrarily writing so that
|
|
// proper control dependencies will be maintained, it never aliases any
|
|
// particular memory location.
|
|
if (isIntrinsicCall(CS, Intrinsic::assume))
|
|
return ModRefInfo::NoModRef;
|
|
|
|
// Like assumes, guard intrinsics are also marked as arbitrarily writing so
|
|
// that proper control dependencies are maintained but they never mods any
|
|
// particular memory location.
|
|
//
|
|
// *Unlike* assumes, guard intrinsics are modeled as reading memory since the
|
|
// heap state at the point the guard is issued needs to be consistent in case
|
|
// the guard invokes the "deopt" continuation.
|
|
if (isIntrinsicCall(CS, Intrinsic::experimental_guard))
|
|
return ModRefInfo::Ref;
|
|
|
|
// Like assumes, invariant.start intrinsics were also marked as arbitrarily
|
|
// writing so that proper control dependencies are maintained but they never
|
|
// mod any particular memory location visible to the IR.
|
|
// *Unlike* assumes (which are now modeled as NoModRef), invariant.start
|
|
// intrinsic is now modeled as reading memory. This prevents hoisting the
|
|
// invariant.start intrinsic over stores. Consider:
|
|
// *ptr = 40;
|
|
// *ptr = 50;
|
|
// invariant_start(ptr)
|
|
// int val = *ptr;
|
|
// print(val);
|
|
//
|
|
// This cannot be transformed to:
|
|
//
|
|
// *ptr = 40;
|
|
// invariant_start(ptr)
|
|
// *ptr = 50;
|
|
// int val = *ptr;
|
|
// print(val);
|
|
//
|
|
// The transformation will cause the second store to be ignored (based on
|
|
// rules of invariant.start) and print 40, while the first program always
|
|
// prints 50.
|
|
if (isIntrinsicCall(CS, Intrinsic::invariant_start))
|
|
return ModRefInfo::Ref;
|
|
|
|
// The AAResultBase base class has some smarts, lets use them.
|
|
return AAResultBase::getModRefInfo(CS, Loc);
|
|
}
|
|
|
|
ModRefInfo BasicAAResult::getModRefInfo(ImmutableCallSite CS1,
|
|
ImmutableCallSite CS2) {
|
|
// While the assume intrinsic is marked as arbitrarily writing so that
|
|
// proper control dependencies will be maintained, it never aliases any
|
|
// particular memory location.
|
|
if (isIntrinsicCall(CS1, Intrinsic::assume) ||
|
|
isIntrinsicCall(CS2, Intrinsic::assume))
|
|
return ModRefInfo::NoModRef;
|
|
|
|
// Like assumes, guard intrinsics are also marked as arbitrarily writing so
|
|
// that proper control dependencies are maintained but they never mod any
|
|
// particular memory location.
|
|
//
|
|
// *Unlike* assumes, guard intrinsics are modeled as reading memory since the
|
|
// heap state at the point the guard is issued needs to be consistent in case
|
|
// the guard invokes the "deopt" continuation.
|
|
|
|
// NB! This function is *not* commutative, so we specical case two
|
|
// possibilities for guard intrinsics.
|
|
|
|
if (isIntrinsicCall(CS1, Intrinsic::experimental_guard))
|
|
return isModSet(createModRefInfo(getModRefBehavior(CS2)))
|
|
? ModRefInfo::Ref
|
|
: ModRefInfo::NoModRef;
|
|
|
|
if (isIntrinsicCall(CS2, Intrinsic::experimental_guard))
|
|
return isModSet(createModRefInfo(getModRefBehavior(CS1)))
|
|
? ModRefInfo::Mod
|
|
: ModRefInfo::NoModRef;
|
|
|
|
// The AAResultBase base class has some smarts, lets use them.
|
|
return AAResultBase::getModRefInfo(CS1, CS2);
|
|
}
|
|
|
|
/// Provide ad-hoc rules to disambiguate accesses through two GEP operators,
|
|
/// both having the exact same pointer operand.
|
|
static AliasResult aliasSameBasePointerGEPs(const GEPOperator *GEP1,
|
|
uint64_t V1Size,
|
|
const GEPOperator *GEP2,
|
|
uint64_t V2Size,
|
|
const DataLayout &DL) {
|
|
assert(GEP1->getPointerOperand()->stripPointerCastsAndBarriers() ==
|
|
GEP2->getPointerOperand()->stripPointerCastsAndBarriers() &&
|
|
GEP1->getPointerOperandType() == GEP2->getPointerOperandType() &&
|
|
"Expected GEPs with the same pointer operand");
|
|
|
|
// Try to determine whether GEP1 and GEP2 index through arrays, into structs,
|
|
// such that the struct field accesses provably cannot alias.
|
|
// We also need at least two indices (the pointer, and the struct field).
|
|
if (GEP1->getNumIndices() != GEP2->getNumIndices() ||
|
|
GEP1->getNumIndices() < 2)
|
|
return MayAlias;
|
|
|
|
// If we don't know the size of the accesses through both GEPs, we can't
|
|
// determine whether the struct fields accessed can't alias.
|
|
if (V1Size == MemoryLocation::UnknownSize ||
|
|
V2Size == MemoryLocation::UnknownSize)
|
|
return MayAlias;
|
|
|
|
ConstantInt *C1 =
|
|
dyn_cast<ConstantInt>(GEP1->getOperand(GEP1->getNumOperands() - 1));
|
|
ConstantInt *C2 =
|
|
dyn_cast<ConstantInt>(GEP2->getOperand(GEP2->getNumOperands() - 1));
|
|
|
|
// If the last (struct) indices are constants and are equal, the other indices
|
|
// might be also be dynamically equal, so the GEPs can alias.
|
|
if (C1 && C2 && C1->getSExtValue() == C2->getSExtValue())
|
|
return MayAlias;
|
|
|
|
// Find the last-indexed type of the GEP, i.e., the type you'd get if
|
|
// you stripped the last index.
|
|
// On the way, look at each indexed type. If there's something other
|
|
// than an array, different indices can lead to different final types.
|
|
SmallVector<Value *, 8> IntermediateIndices;
|
|
|
|
// Insert the first index; we don't need to check the type indexed
|
|
// through it as it only drops the pointer indirection.
|
|
assert(GEP1->getNumIndices() > 1 && "Not enough GEP indices to examine");
|
|
IntermediateIndices.push_back(GEP1->getOperand(1));
|
|
|
|
// Insert all the remaining indices but the last one.
|
|
// Also, check that they all index through arrays.
|
|
for (unsigned i = 1, e = GEP1->getNumIndices() - 1; i != e; ++i) {
|
|
if (!isa<ArrayType>(GetElementPtrInst::getIndexedType(
|
|
GEP1->getSourceElementType(), IntermediateIndices)))
|
|
return MayAlias;
|
|
IntermediateIndices.push_back(GEP1->getOperand(i + 1));
|
|
}
|
|
|
|
auto *Ty = GetElementPtrInst::getIndexedType(
|
|
GEP1->getSourceElementType(), IntermediateIndices);
|
|
StructType *LastIndexedStruct = dyn_cast<StructType>(Ty);
|
|
|
|
if (isa<SequentialType>(Ty)) {
|
|
// We know that:
|
|
// - both GEPs begin indexing from the exact same pointer;
|
|
// - the last indices in both GEPs are constants, indexing into a sequential
|
|
// type (array or pointer);
|
|
// - both GEPs only index through arrays prior to that.
|
|
//
|
|
// Because array indices greater than the number of elements are valid in
|
|
// GEPs, unless we know the intermediate indices are identical between
|
|
// GEP1 and GEP2 we cannot guarantee that the last indexed arrays don't
|
|
// partially overlap. We also need to check that the loaded size matches
|
|
// the element size, otherwise we could still have overlap.
|
|
const uint64_t ElementSize =
|
|
DL.getTypeStoreSize(cast<SequentialType>(Ty)->getElementType());
|
|
if (V1Size != ElementSize || V2Size != ElementSize)
|
|
return MayAlias;
|
|
|
|
for (unsigned i = 0, e = GEP1->getNumIndices() - 1; i != e; ++i)
|
|
if (GEP1->getOperand(i + 1) != GEP2->getOperand(i + 1))
|
|
return MayAlias;
|
|
|
|
// Now we know that the array/pointer that GEP1 indexes into and that
|
|
// that GEP2 indexes into must either precisely overlap or be disjoint.
|
|
// Because they cannot partially overlap and because fields in an array
|
|
// cannot overlap, if we can prove the final indices are different between
|
|
// GEP1 and GEP2, we can conclude GEP1 and GEP2 don't alias.
|
|
|
|
// If the last indices are constants, we've already checked they don't
|
|
// equal each other so we can exit early.
|
|
if (C1 && C2)
|
|
return NoAlias;
|
|
{
|
|
Value *GEP1LastIdx = GEP1->getOperand(GEP1->getNumOperands() - 1);
|
|
Value *GEP2LastIdx = GEP2->getOperand(GEP2->getNumOperands() - 1);
|
|
if (isa<PHINode>(GEP1LastIdx) || isa<PHINode>(GEP2LastIdx)) {
|
|
// If one of the indices is a PHI node, be safe and only use
|
|
// computeKnownBits so we don't make any assumptions about the
|
|
// relationships between the two indices. This is important if we're
|
|
// asking about values from different loop iterations. See PR32314.
|
|
// TODO: We may be able to change the check so we only do this when
|
|
// we definitely looked through a PHINode.
|
|
if (GEP1LastIdx != GEP2LastIdx &&
|
|
GEP1LastIdx->getType() == GEP2LastIdx->getType()) {
|
|
KnownBits Known1 = computeKnownBits(GEP1LastIdx, DL);
|
|
KnownBits Known2 = computeKnownBits(GEP2LastIdx, DL);
|
|
if (Known1.Zero.intersects(Known2.One) ||
|
|
Known1.One.intersects(Known2.Zero))
|
|
return NoAlias;
|
|
}
|
|
} else if (isKnownNonEqual(GEP1LastIdx, GEP2LastIdx, DL))
|
|
return NoAlias;
|
|
}
|
|
return MayAlias;
|
|
} else if (!LastIndexedStruct || !C1 || !C2) {
|
|
return MayAlias;
|
|
}
|
|
|
|
// We know that:
|
|
// - both GEPs begin indexing from the exact same pointer;
|
|
// - the last indices in both GEPs are constants, indexing into a struct;
|
|
// - said indices are different, hence, the pointed-to fields are different;
|
|
// - both GEPs only index through arrays prior to that.
|
|
//
|
|
// This lets us determine that the struct that GEP1 indexes into and the
|
|
// struct that GEP2 indexes into must either precisely overlap or be
|
|
// completely disjoint. Because they cannot partially overlap, indexing into
|
|
// different non-overlapping fields of the struct will never alias.
|
|
|
|
// Therefore, the only remaining thing needed to show that both GEPs can't
|
|
// alias is that the fields are not overlapping.
|
|
const StructLayout *SL = DL.getStructLayout(LastIndexedStruct);
|
|
const uint64_t StructSize = SL->getSizeInBytes();
|
|
const uint64_t V1Off = SL->getElementOffset(C1->getZExtValue());
|
|
const uint64_t V2Off = SL->getElementOffset(C2->getZExtValue());
|
|
|
|
auto EltsDontOverlap = [StructSize](uint64_t V1Off, uint64_t V1Size,
|
|
uint64_t V2Off, uint64_t V2Size) {
|
|
return V1Off < V2Off && V1Off + V1Size <= V2Off &&
|
|
((V2Off + V2Size <= StructSize) ||
|
|
(V2Off + V2Size - StructSize <= V1Off));
|
|
};
|
|
|
|
if (EltsDontOverlap(V1Off, V1Size, V2Off, V2Size) ||
|
|
EltsDontOverlap(V2Off, V2Size, V1Off, V1Size))
|
|
return NoAlias;
|
|
|
|
return MayAlias;
|
|
}
|
|
|
|
// If a we have (a) a GEP and (b) a pointer based on an alloca, and the
|
|
// beginning of the object the GEP points would have a negative offset with
|
|
// repsect to the alloca, that means the GEP can not alias pointer (b).
|
|
// Note that the pointer based on the alloca may not be a GEP. For
|
|
// example, it may be the alloca itself.
|
|
// The same applies if (b) is based on a GlobalVariable. Note that just being
|
|
// based on isIdentifiedObject() is not enough - we need an identified object
|
|
// that does not permit access to negative offsets. For example, a negative
|
|
// offset from a noalias argument or call can be inbounds w.r.t the actual
|
|
// underlying object.
|
|
//
|
|
// For example, consider:
|
|
//
|
|
// struct { int f0, int f1, ...} foo;
|
|
// foo alloca;
|
|
// foo* random = bar(alloca);
|
|
// int *f0 = &alloca.f0
|
|
// int *f1 = &random->f1;
|
|
//
|
|
// Which is lowered, approximately, to:
|
|
//
|
|
// %alloca = alloca %struct.foo
|
|
// %random = call %struct.foo* @random(%struct.foo* %alloca)
|
|
// %f0 = getelementptr inbounds %struct, %struct.foo* %alloca, i32 0, i32 0
|
|
// %f1 = getelementptr inbounds %struct, %struct.foo* %random, i32 0, i32 1
|
|
//
|
|
// Assume %f1 and %f0 alias. Then %f1 would point into the object allocated
|
|
// by %alloca. Since the %f1 GEP is inbounds, that means %random must also
|
|
// point into the same object. But since %f0 points to the beginning of %alloca,
|
|
// the highest %f1 can be is (%alloca + 3). This means %random can not be higher
|
|
// than (%alloca - 1), and so is not inbounds, a contradiction.
|
|
bool BasicAAResult::isGEPBaseAtNegativeOffset(const GEPOperator *GEPOp,
|
|
const DecomposedGEP &DecompGEP, const DecomposedGEP &DecompObject,
|
|
uint64_t ObjectAccessSize) {
|
|
// If the object access size is unknown, or the GEP isn't inbounds, bail.
|
|
if (ObjectAccessSize == MemoryLocation::UnknownSize || !GEPOp->isInBounds())
|
|
return false;
|
|
|
|
// We need the object to be an alloca or a globalvariable, and want to know
|
|
// the offset of the pointer from the object precisely, so no variable
|
|
// indices are allowed.
|
|
if (!(isa<AllocaInst>(DecompObject.Base) ||
|
|
isa<GlobalVariable>(DecompObject.Base)) ||
|
|
!DecompObject.VarIndices.empty())
|
|
return false;
|
|
|
|
int64_t ObjectBaseOffset = DecompObject.StructOffset +
|
|
DecompObject.OtherOffset;
|
|
|
|
// If the GEP has no variable indices, we know the precise offset
|
|
// from the base, then use it. If the GEP has variable indices, we're in
|
|
// a bit more trouble: we can't count on the constant offsets that come
|
|
// from non-struct sources, since these can be "rewound" by a negative
|
|
// variable offset. So use only offsets that came from structs.
|
|
int64_t GEPBaseOffset = DecompGEP.StructOffset;
|
|
if (DecompGEP.VarIndices.empty())
|
|
GEPBaseOffset += DecompGEP.OtherOffset;
|
|
|
|
return (GEPBaseOffset >= ObjectBaseOffset + (int64_t)ObjectAccessSize);
|
|
}
|
|
|
|
/// Provides a bunch of ad-hoc rules to disambiguate a GEP instruction against
|
|
/// another pointer.
|
|
///
|
|
/// We know that V1 is a GEP, but we don't know anything about V2.
|
|
/// UnderlyingV1 is GetUnderlyingObject(GEP1, DL), UnderlyingV2 is the same for
|
|
/// V2.
|
|
AliasResult BasicAAResult::aliasGEP(const GEPOperator *GEP1, uint64_t V1Size,
|
|
const AAMDNodes &V1AAInfo, const Value *V2,
|
|
uint64_t V2Size, const AAMDNodes &V2AAInfo,
|
|
const Value *UnderlyingV1,
|
|
const Value *UnderlyingV2) {
|
|
DecomposedGEP DecompGEP1, DecompGEP2;
|
|
bool GEP1MaxLookupReached =
|
|
DecomposeGEPExpression(GEP1, DecompGEP1, DL, &AC, DT);
|
|
bool GEP2MaxLookupReached =
|
|
DecomposeGEPExpression(V2, DecompGEP2, DL, &AC, DT);
|
|
|
|
int64_t GEP1BaseOffset = DecompGEP1.StructOffset + DecompGEP1.OtherOffset;
|
|
int64_t GEP2BaseOffset = DecompGEP2.StructOffset + DecompGEP2.OtherOffset;
|
|
|
|
assert(DecompGEP1.Base == UnderlyingV1 && DecompGEP2.Base == UnderlyingV2 &&
|
|
"DecomposeGEPExpression returned a result different from "
|
|
"GetUnderlyingObject");
|
|
|
|
// If the GEP's offset relative to its base is such that the base would
|
|
// fall below the start of the object underlying V2, then the GEP and V2
|
|
// cannot alias.
|
|
if (!GEP1MaxLookupReached && !GEP2MaxLookupReached &&
|
|
isGEPBaseAtNegativeOffset(GEP1, DecompGEP1, DecompGEP2, V2Size))
|
|
return NoAlias;
|
|
// If we have two gep instructions with must-alias or not-alias'ing base
|
|
// pointers, figure out if the indexes to the GEP tell us anything about the
|
|
// derived pointer.
|
|
if (const GEPOperator *GEP2 = dyn_cast<GEPOperator>(V2)) {
|
|
// Check for the GEP base being at a negative offset, this time in the other
|
|
// direction.
|
|
if (!GEP1MaxLookupReached && !GEP2MaxLookupReached &&
|
|
isGEPBaseAtNegativeOffset(GEP2, DecompGEP2, DecompGEP1, V1Size))
|
|
return NoAlias;
|
|
// Do the base pointers alias?
|
|
AliasResult BaseAlias =
|
|
aliasCheck(UnderlyingV1, MemoryLocation::UnknownSize, AAMDNodes(),
|
|
UnderlyingV2, MemoryLocation::UnknownSize, AAMDNodes());
|
|
|
|
// Check for geps of non-aliasing underlying pointers where the offsets are
|
|
// identical.
|
|
if ((BaseAlias == MayAlias) && V1Size == V2Size) {
|
|
// Do the base pointers alias assuming type and size.
|
|
AliasResult PreciseBaseAlias = aliasCheck(UnderlyingV1, V1Size, V1AAInfo,
|
|
UnderlyingV2, V2Size, V2AAInfo);
|
|
if (PreciseBaseAlias == NoAlias) {
|
|
// See if the computed offset from the common pointer tells us about the
|
|
// relation of the resulting pointer.
|
|
// If the max search depth is reached the result is undefined
|
|
if (GEP2MaxLookupReached || GEP1MaxLookupReached)
|
|
return MayAlias;
|
|
|
|
// Same offsets.
|
|
if (GEP1BaseOffset == GEP2BaseOffset &&
|
|
DecompGEP1.VarIndices == DecompGEP2.VarIndices)
|
|
return NoAlias;
|
|
}
|
|
}
|
|
|
|
// If we get a No or May, then return it immediately, no amount of analysis
|
|
// will improve this situation.
|
|
if (BaseAlias != MustAlias) {
|
|
assert(BaseAlias == NoAlias || BaseAlias == MayAlias);
|
|
return BaseAlias;
|
|
}
|
|
|
|
// Otherwise, we have a MustAlias. Since the base pointers alias each other
|
|
// exactly, see if the computed offset from the common pointer tells us
|
|
// about the relation of the resulting pointer.
|
|
// If we know the two GEPs are based off of the exact same pointer (and not
|
|
// just the same underlying object), see if that tells us anything about
|
|
// the resulting pointers.
|
|
if (GEP1->getPointerOperand()->stripPointerCastsAndBarriers() ==
|
|
GEP2->getPointerOperand()->stripPointerCastsAndBarriers() &&
|
|
GEP1->getPointerOperandType() == GEP2->getPointerOperandType()) {
|
|
AliasResult R = aliasSameBasePointerGEPs(GEP1, V1Size, GEP2, V2Size, DL);
|
|
// If we couldn't find anything interesting, don't abandon just yet.
|
|
if (R != MayAlias)
|
|
return R;
|
|
}
|
|
|
|
// If the max search depth is reached, the result is undefined
|
|
if (GEP2MaxLookupReached || GEP1MaxLookupReached)
|
|
return MayAlias;
|
|
|
|
// Subtract the GEP2 pointer from the GEP1 pointer to find out their
|
|
// symbolic difference.
|
|
GEP1BaseOffset -= GEP2BaseOffset;
|
|
GetIndexDifference(DecompGEP1.VarIndices, DecompGEP2.VarIndices);
|
|
|
|
} else {
|
|
// Check to see if these two pointers are related by the getelementptr
|
|
// instruction. If one pointer is a GEP with a non-zero index of the other
|
|
// pointer, we know they cannot alias.
|
|
|
|
// If both accesses are unknown size, we can't do anything useful here.
|
|
if (V1Size == MemoryLocation::UnknownSize &&
|
|
V2Size == MemoryLocation::UnknownSize)
|
|
return MayAlias;
|
|
|
|
AliasResult R = aliasCheck(UnderlyingV1, MemoryLocation::UnknownSize,
|
|
AAMDNodes(), V2, MemoryLocation::UnknownSize,
|
|
V2AAInfo, nullptr, UnderlyingV2);
|
|
if (R != MustAlias) {
|
|
// If V2 may alias GEP base pointer, conservatively returns MayAlias.
|
|
// If V2 is known not to alias GEP base pointer, then the two values
|
|
// cannot alias per GEP semantics: "Any memory access must be done through
|
|
// a pointer value associated with an address range of the memory access,
|
|
// otherwise the behavior is undefined.".
|
|
assert(R == NoAlias || R == MayAlias);
|
|
return R;
|
|
}
|
|
|
|
// If the max search depth is reached the result is undefined
|
|
if (GEP1MaxLookupReached)
|
|
return MayAlias;
|
|
}
|
|
|
|
// In the two GEP Case, if there is no difference in the offsets of the
|
|
// computed pointers, the resultant pointers are a must alias. This
|
|
// happens when we have two lexically identical GEP's (for example).
|
|
//
|
|
// In the other case, if we have getelementptr <ptr>, 0, 0, 0, 0, ... and V2
|
|
// must aliases the GEP, the end result is a must alias also.
|
|
if (GEP1BaseOffset == 0 && DecompGEP1.VarIndices.empty())
|
|
return MustAlias;
|
|
|
|
// If there is a constant difference between the pointers, but the difference
|
|
// is less than the size of the associated memory object, then we know
|
|
// that the objects are partially overlapping. If the difference is
|
|
// greater, we know they do not overlap.
|
|
if (GEP1BaseOffset != 0 && DecompGEP1.VarIndices.empty()) {
|
|
if (GEP1BaseOffset >= 0) {
|
|
if (V2Size != MemoryLocation::UnknownSize) {
|
|
if ((uint64_t)GEP1BaseOffset < V2Size)
|
|
return PartialAlias;
|
|
return NoAlias;
|
|
}
|
|
} else {
|
|
// We have the situation where:
|
|
// + +
|
|
// | BaseOffset |
|
|
// ---------------->|
|
|
// |-->V1Size |-------> V2Size
|
|
// GEP1 V2
|
|
// We need to know that V2Size is not unknown, otherwise we might have
|
|
// stripped a gep with negative index ('gep <ptr>, -1, ...).
|
|
if (V1Size != MemoryLocation::UnknownSize &&
|
|
V2Size != MemoryLocation::UnknownSize) {
|
|
if (-(uint64_t)GEP1BaseOffset < V1Size)
|
|
return PartialAlias;
|
|
return NoAlias;
|
|
}
|
|
}
|
|
}
|
|
|
|
if (!DecompGEP1.VarIndices.empty()) {
|
|
uint64_t Modulo = 0;
|
|
bool AllPositive = true;
|
|
for (unsigned i = 0, e = DecompGEP1.VarIndices.size(); i != e; ++i) {
|
|
|
|
// Try to distinguish something like &A[i][1] against &A[42][0].
|
|
// Grab the least significant bit set in any of the scales. We
|
|
// don't need std::abs here (even if the scale's negative) as we'll
|
|
// be ^'ing Modulo with itself later.
|
|
Modulo |= (uint64_t)DecompGEP1.VarIndices[i].Scale;
|
|
|
|
if (AllPositive) {
|
|
// If the Value could change between cycles, then any reasoning about
|
|
// the Value this cycle may not hold in the next cycle. We'll just
|
|
// give up if we can't determine conditions that hold for every cycle:
|
|
const Value *V = DecompGEP1.VarIndices[i].V;
|
|
|
|
KnownBits Known = computeKnownBits(V, DL, 0, &AC, nullptr, DT);
|
|
bool SignKnownZero = Known.isNonNegative();
|
|
bool SignKnownOne = Known.isNegative();
|
|
|
|
// Zero-extension widens the variable, and so forces the sign
|
|
// bit to zero.
|
|
bool IsZExt = DecompGEP1.VarIndices[i].ZExtBits > 0 || isa<ZExtInst>(V);
|
|
SignKnownZero |= IsZExt;
|
|
SignKnownOne &= !IsZExt;
|
|
|
|
// If the variable begins with a zero then we know it's
|
|
// positive, regardless of whether the value is signed or
|
|
// unsigned.
|
|
int64_t Scale = DecompGEP1.VarIndices[i].Scale;
|
|
AllPositive =
|
|
(SignKnownZero && Scale >= 0) || (SignKnownOne && Scale < 0);
|
|
}
|
|
}
|
|
|
|
Modulo = Modulo ^ (Modulo & (Modulo - 1));
|
|
|
|
// We can compute the difference between the two addresses
|
|
// mod Modulo. Check whether that difference guarantees that the
|
|
// two locations do not alias.
|
|
uint64_t ModOffset = (uint64_t)GEP1BaseOffset & (Modulo - 1);
|
|
if (V1Size != MemoryLocation::UnknownSize &&
|
|
V2Size != MemoryLocation::UnknownSize && ModOffset >= V2Size &&
|
|
V1Size <= Modulo - ModOffset)
|
|
return NoAlias;
|
|
|
|
// If we know all the variables are positive, then GEP1 >= GEP1BasePtr.
|
|
// If GEP1BasePtr > V2 (GEP1BaseOffset > 0) then we know the pointers
|
|
// don't alias if V2Size can fit in the gap between V2 and GEP1BasePtr.
|
|
if (AllPositive && GEP1BaseOffset > 0 && V2Size <= (uint64_t)GEP1BaseOffset)
|
|
return NoAlias;
|
|
|
|
if (constantOffsetHeuristic(DecompGEP1.VarIndices, V1Size, V2Size,
|
|
GEP1BaseOffset, &AC, DT))
|
|
return NoAlias;
|
|
}
|
|
|
|
// Statically, we can see that the base objects are the same, but the
|
|
// pointers have dynamic offsets which we can't resolve. And none of our
|
|
// little tricks above worked.
|
|
return MayAlias;
|
|
}
|
|
|
|
static AliasResult MergeAliasResults(AliasResult A, AliasResult B) {
|
|
// If the results agree, take it.
|
|
if (A == B)
|
|
return A;
|
|
// A mix of PartialAlias and MustAlias is PartialAlias.
|
|
if ((A == PartialAlias && B == MustAlias) ||
|
|
(B == PartialAlias && A == MustAlias))
|
|
return PartialAlias;
|
|
// Otherwise, we don't know anything.
|
|
return MayAlias;
|
|
}
|
|
|
|
/// Provides a bunch of ad-hoc rules to disambiguate a Select instruction
|
|
/// against another.
|
|
AliasResult BasicAAResult::aliasSelect(const SelectInst *SI, uint64_t SISize,
|
|
const AAMDNodes &SIAAInfo,
|
|
const Value *V2, uint64_t V2Size,
|
|
const AAMDNodes &V2AAInfo,
|
|
const Value *UnderV2) {
|
|
// If the values are Selects with the same condition, we can do a more precise
|
|
// check: just check for aliases between the values on corresponding arms.
|
|
if (const SelectInst *SI2 = dyn_cast<SelectInst>(V2))
|
|
if (SI->getCondition() == SI2->getCondition()) {
|
|
AliasResult Alias = aliasCheck(SI->getTrueValue(), SISize, SIAAInfo,
|
|
SI2->getTrueValue(), V2Size, V2AAInfo);
|
|
if (Alias == MayAlias)
|
|
return MayAlias;
|
|
AliasResult ThisAlias =
|
|
aliasCheck(SI->getFalseValue(), SISize, SIAAInfo,
|
|
SI2->getFalseValue(), V2Size, V2AAInfo);
|
|
return MergeAliasResults(ThisAlias, Alias);
|
|
}
|
|
|
|
// If both arms of the Select node NoAlias or MustAlias V2, then returns
|
|
// NoAlias / MustAlias. Otherwise, returns MayAlias.
|
|
AliasResult Alias =
|
|
aliasCheck(V2, V2Size, V2AAInfo, SI->getTrueValue(),
|
|
SISize, SIAAInfo, UnderV2);
|
|
if (Alias == MayAlias)
|
|
return MayAlias;
|
|
|
|
AliasResult ThisAlias =
|
|
aliasCheck(V2, V2Size, V2AAInfo, SI->getFalseValue(), SISize, SIAAInfo,
|
|
UnderV2);
|
|
return MergeAliasResults(ThisAlias, Alias);
|
|
}
|
|
|
|
/// Provide a bunch of ad-hoc rules to disambiguate a PHI instruction against
|
|
/// another.
|
|
AliasResult BasicAAResult::aliasPHI(const PHINode *PN, uint64_t PNSize,
|
|
const AAMDNodes &PNAAInfo, const Value *V2,
|
|
uint64_t V2Size, const AAMDNodes &V2AAInfo,
|
|
const Value *UnderV2) {
|
|
// Track phi nodes we have visited. We use this information when we determine
|
|
// value equivalence.
|
|
VisitedPhiBBs.insert(PN->getParent());
|
|
|
|
// If the values are PHIs in the same block, we can do a more precise
|
|
// as well as efficient check: just check for aliases between the values
|
|
// on corresponding edges.
|
|
if (const PHINode *PN2 = dyn_cast<PHINode>(V2))
|
|
if (PN2->getParent() == PN->getParent()) {
|
|
LocPair Locs(MemoryLocation(PN, PNSize, PNAAInfo),
|
|
MemoryLocation(V2, V2Size, V2AAInfo));
|
|
if (PN > V2)
|
|
std::swap(Locs.first, Locs.second);
|
|
// Analyse the PHIs' inputs under the assumption that the PHIs are
|
|
// NoAlias.
|
|
// If the PHIs are May/MustAlias there must be (recursively) an input
|
|
// operand from outside the PHIs' cycle that is MayAlias/MustAlias or
|
|
// there must be an operation on the PHIs within the PHIs' value cycle
|
|
// that causes a MayAlias.
|
|
// Pretend the phis do not alias.
|
|
AliasResult Alias = NoAlias;
|
|
assert(AliasCache.count(Locs) &&
|
|
"There must exist an entry for the phi node");
|
|
AliasResult OrigAliasResult = AliasCache[Locs];
|
|
AliasCache[Locs] = NoAlias;
|
|
|
|
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
|
|
AliasResult ThisAlias =
|
|
aliasCheck(PN->getIncomingValue(i), PNSize, PNAAInfo,
|
|
PN2->getIncomingValueForBlock(PN->getIncomingBlock(i)),
|
|
V2Size, V2AAInfo);
|
|
Alias = MergeAliasResults(ThisAlias, Alias);
|
|
if (Alias == MayAlias)
|
|
break;
|
|
}
|
|
|
|
// Reset if speculation failed.
|
|
if (Alias != NoAlias)
|
|
AliasCache[Locs] = OrigAliasResult;
|
|
|
|
return Alias;
|
|
}
|
|
|
|
SmallPtrSet<Value *, 4> UniqueSrc;
|
|
SmallVector<Value *, 4> V1Srcs;
|
|
bool isRecursive = false;
|
|
for (Value *PV1 : PN->incoming_values()) {
|
|
if (isa<PHINode>(PV1))
|
|
// If any of the source itself is a PHI, return MayAlias conservatively
|
|
// to avoid compile time explosion. The worst possible case is if both
|
|
// sides are PHI nodes. In which case, this is O(m x n) time where 'm'
|
|
// and 'n' are the number of PHI sources.
|
|
return MayAlias;
|
|
|
|
if (EnableRecPhiAnalysis)
|
|
if (GEPOperator *PV1GEP = dyn_cast<GEPOperator>(PV1)) {
|
|
// Check whether the incoming value is a GEP that advances the pointer
|
|
// result of this PHI node (e.g. in a loop). If this is the case, we
|
|
// would recurse and always get a MayAlias. Handle this case specially
|
|
// below.
|
|
if (PV1GEP->getPointerOperand() == PN && PV1GEP->getNumIndices() == 1 &&
|
|
isa<ConstantInt>(PV1GEP->idx_begin())) {
|
|
isRecursive = true;
|
|
continue;
|
|
}
|
|
}
|
|
|
|
if (UniqueSrc.insert(PV1).second)
|
|
V1Srcs.push_back(PV1);
|
|
}
|
|
|
|
// If this PHI node is recursive, set the size of the accessed memory to
|
|
// unknown to represent all the possible values the GEP could advance the
|
|
// pointer to.
|
|
if (isRecursive)
|
|
PNSize = MemoryLocation::UnknownSize;
|
|
|
|
AliasResult Alias =
|
|
aliasCheck(V2, V2Size, V2AAInfo, V1Srcs[0],
|
|
PNSize, PNAAInfo, UnderV2);
|
|
|
|
// Early exit if the check of the first PHI source against V2 is MayAlias.
|
|
// Other results are not possible.
|
|
if (Alias == MayAlias)
|
|
return MayAlias;
|
|
|
|
// If all sources of the PHI node NoAlias or MustAlias V2, then returns
|
|
// NoAlias / MustAlias. Otherwise, returns MayAlias.
|
|
for (unsigned i = 1, e = V1Srcs.size(); i != e; ++i) {
|
|
Value *V = V1Srcs[i];
|
|
|
|
AliasResult ThisAlias =
|
|
aliasCheck(V2, V2Size, V2AAInfo, V, PNSize, PNAAInfo, UnderV2);
|
|
Alias = MergeAliasResults(ThisAlias, Alias);
|
|
if (Alias == MayAlias)
|
|
break;
|
|
}
|
|
|
|
return Alias;
|
|
}
|
|
|
|
/// Provides a bunch of ad-hoc rules to disambiguate in common cases, such as
|
|
/// array references.
|
|
AliasResult BasicAAResult::aliasCheck(const Value *V1, uint64_t V1Size,
|
|
AAMDNodes V1AAInfo, const Value *V2,
|
|
uint64_t V2Size, AAMDNodes V2AAInfo,
|
|
const Value *O1, const Value *O2) {
|
|
// If either of the memory references is empty, it doesn't matter what the
|
|
// pointer values are.
|
|
if (V1Size == 0 || V2Size == 0)
|
|
return NoAlias;
|
|
|
|
// Strip off any casts if they exist.
|
|
V1 = V1->stripPointerCastsAndBarriers();
|
|
V2 = V2->stripPointerCastsAndBarriers();
|
|
|
|
// If V1 or V2 is undef, the result is NoAlias because we can always pick a
|
|
// value for undef that aliases nothing in the program.
|
|
if (isa<UndefValue>(V1) || isa<UndefValue>(V2))
|
|
return NoAlias;
|
|
|
|
// Are we checking for alias of the same value?
|
|
// Because we look 'through' phi nodes, we could look at "Value" pointers from
|
|
// different iterations. We must therefore make sure that this is not the
|
|
// case. The function isValueEqualInPotentialCycles ensures that this cannot
|
|
// happen by looking at the visited phi nodes and making sure they cannot
|
|
// reach the value.
|
|
if (isValueEqualInPotentialCycles(V1, V2))
|
|
return MustAlias;
|
|
|
|
if (!V1->getType()->isPointerTy() || !V2->getType()->isPointerTy())
|
|
return NoAlias; // Scalars cannot alias each other
|
|
|
|
// Figure out what objects these things are pointing to if we can.
|
|
if (O1 == nullptr)
|
|
O1 = GetUnderlyingObject(V1, DL, MaxLookupSearchDepth);
|
|
|
|
if (O2 == nullptr)
|
|
O2 = GetUnderlyingObject(V2, DL, MaxLookupSearchDepth);
|
|
|
|
// Null values in the default address space don't point to any object, so they
|
|
// don't alias any other pointer.
|
|
if (const ConstantPointerNull *CPN = dyn_cast<ConstantPointerNull>(O1))
|
|
if (CPN->getType()->getAddressSpace() == 0)
|
|
return NoAlias;
|
|
if (const ConstantPointerNull *CPN = dyn_cast<ConstantPointerNull>(O2))
|
|
if (CPN->getType()->getAddressSpace() == 0)
|
|
return NoAlias;
|
|
|
|
if (O1 != O2) {
|
|
// If V1/V2 point to two different objects, we know that we have no alias.
|
|
if (isIdentifiedObject(O1) && isIdentifiedObject(O2))
|
|
return NoAlias;
|
|
|
|
// Constant pointers can't alias with non-const isIdentifiedObject objects.
|
|
if ((isa<Constant>(O1) && isIdentifiedObject(O2) && !isa<Constant>(O2)) ||
|
|
(isa<Constant>(O2) && isIdentifiedObject(O1) && !isa<Constant>(O1)))
|
|
return NoAlias;
|
|
|
|
// Function arguments can't alias with things that are known to be
|
|
// unambigously identified at the function level.
|
|
if ((isa<Argument>(O1) && isIdentifiedFunctionLocal(O2)) ||
|
|
(isa<Argument>(O2) && isIdentifiedFunctionLocal(O1)))
|
|
return NoAlias;
|
|
|
|
// If one pointer is the result of a call/invoke or load and the other is a
|
|
// non-escaping local object within the same function, then we know the
|
|
// object couldn't escape to a point where the call could return it.
|
|
//
|
|
// Note that if the pointers are in different functions, there are a
|
|
// variety of complications. A call with a nocapture argument may still
|
|
// temporary store the nocapture argument's value in a temporary memory
|
|
// location if that memory location doesn't escape. Or it may pass a
|
|
// nocapture value to other functions as long as they don't capture it.
|
|
if (isEscapeSource(O1) && isNonEscapingLocalObject(O2))
|
|
return NoAlias;
|
|
if (isEscapeSource(O2) && isNonEscapingLocalObject(O1))
|
|
return NoAlias;
|
|
}
|
|
|
|
// If the size of one access is larger than the entire object on the other
|
|
// side, then we know such behavior is undefined and can assume no alias.
|
|
if ((V1Size != MemoryLocation::UnknownSize &&
|
|
isObjectSmallerThan(O2, V1Size, DL, TLI)) ||
|
|
(V2Size != MemoryLocation::UnknownSize &&
|
|
isObjectSmallerThan(O1, V2Size, DL, TLI)))
|
|
return NoAlias;
|
|
|
|
// Check the cache before climbing up use-def chains. This also terminates
|
|
// otherwise infinitely recursive queries.
|
|
LocPair Locs(MemoryLocation(V1, V1Size, V1AAInfo),
|
|
MemoryLocation(V2, V2Size, V2AAInfo));
|
|
if (V1 > V2)
|
|
std::swap(Locs.first, Locs.second);
|
|
std::pair<AliasCacheTy::iterator, bool> Pair =
|
|
AliasCache.insert(std::make_pair(Locs, MayAlias));
|
|
if (!Pair.second)
|
|
return Pair.first->second;
|
|
|
|
// FIXME: This isn't aggressively handling alias(GEP, PHI) for example: if the
|
|
// GEP can't simplify, we don't even look at the PHI cases.
|
|
if (!isa<GEPOperator>(V1) && isa<GEPOperator>(V2)) {
|
|
std::swap(V1, V2);
|
|
std::swap(V1Size, V2Size);
|
|
std::swap(O1, O2);
|
|
std::swap(V1AAInfo, V2AAInfo);
|
|
}
|
|
if (const GEPOperator *GV1 = dyn_cast<GEPOperator>(V1)) {
|
|
AliasResult Result =
|
|
aliasGEP(GV1, V1Size, V1AAInfo, V2, V2Size, V2AAInfo, O1, O2);
|
|
if (Result != MayAlias)
|
|
return AliasCache[Locs] = Result;
|
|
}
|
|
|
|
if (isa<PHINode>(V2) && !isa<PHINode>(V1)) {
|
|
std::swap(V1, V2);
|
|
std::swap(O1, O2);
|
|
std::swap(V1Size, V2Size);
|
|
std::swap(V1AAInfo, V2AAInfo);
|
|
}
|
|
if (const PHINode *PN = dyn_cast<PHINode>(V1)) {
|
|
AliasResult Result = aliasPHI(PN, V1Size, V1AAInfo,
|
|
V2, V2Size, V2AAInfo, O2);
|
|
if (Result != MayAlias)
|
|
return AliasCache[Locs] = Result;
|
|
}
|
|
|
|
if (isa<SelectInst>(V2) && !isa<SelectInst>(V1)) {
|
|
std::swap(V1, V2);
|
|
std::swap(O1, O2);
|
|
std::swap(V1Size, V2Size);
|
|
std::swap(V1AAInfo, V2AAInfo);
|
|
}
|
|
if (const SelectInst *S1 = dyn_cast<SelectInst>(V1)) {
|
|
AliasResult Result =
|
|
aliasSelect(S1, V1Size, V1AAInfo, V2, V2Size, V2AAInfo, O2);
|
|
if (Result != MayAlias)
|
|
return AliasCache[Locs] = Result;
|
|
}
|
|
|
|
// If both pointers are pointing into the same object and one of them
|
|
// accesses the entire object, then the accesses must overlap in some way.
|
|
if (O1 == O2)
|
|
if (V1Size != MemoryLocation::UnknownSize &&
|
|
V2Size != MemoryLocation::UnknownSize &&
|
|
(isObjectSize(O1, V1Size, DL, TLI) ||
|
|
isObjectSize(O2, V2Size, DL, TLI)))
|
|
return AliasCache[Locs] = PartialAlias;
|
|
|
|
// Recurse back into the best AA results we have, potentially with refined
|
|
// memory locations. We have already ensured that BasicAA has a MayAlias
|
|
// cache result for these, so any recursion back into BasicAA won't loop.
|
|
AliasResult Result = getBestAAResults().alias(Locs.first, Locs.second);
|
|
return AliasCache[Locs] = Result;
|
|
}
|
|
|
|
/// Check whether two Values can be considered equivalent.
|
|
///
|
|
/// In addition to pointer equivalence of \p V1 and \p V2 this checks whether
|
|
/// they can not be part of a cycle in the value graph by looking at all
|
|
/// visited phi nodes an making sure that the phis cannot reach the value. We
|
|
/// have to do this because we are looking through phi nodes (That is we say
|
|
/// noalias(V, phi(VA, VB)) if noalias(V, VA) and noalias(V, VB).
|
|
bool BasicAAResult::isValueEqualInPotentialCycles(const Value *V,
|
|
const Value *V2) {
|
|
if (V != V2)
|
|
return false;
|
|
|
|
const Instruction *Inst = dyn_cast<Instruction>(V);
|
|
if (!Inst)
|
|
return true;
|
|
|
|
if (VisitedPhiBBs.empty())
|
|
return true;
|
|
|
|
if (VisitedPhiBBs.size() > MaxNumPhiBBsValueReachabilityCheck)
|
|
return false;
|
|
|
|
// Make sure that the visited phis cannot reach the Value. This ensures that
|
|
// the Values cannot come from different iterations of a potential cycle the
|
|
// phi nodes could be involved in.
|
|
for (auto *P : VisitedPhiBBs)
|
|
if (isPotentiallyReachable(&P->front(), Inst, DT, LI))
|
|
return false;
|
|
|
|
return true;
|
|
}
|
|
|
|
/// Computes the symbolic difference between two de-composed GEPs.
|
|
///
|
|
/// Dest and Src are the variable indices from two decomposed GetElementPtr
|
|
/// instructions GEP1 and GEP2 which have common base pointers.
|
|
void BasicAAResult::GetIndexDifference(
|
|
SmallVectorImpl<VariableGEPIndex> &Dest,
|
|
const SmallVectorImpl<VariableGEPIndex> &Src) {
|
|
if (Src.empty())
|
|
return;
|
|
|
|
for (unsigned i = 0, e = Src.size(); i != e; ++i) {
|
|
const Value *V = Src[i].V;
|
|
unsigned ZExtBits = Src[i].ZExtBits, SExtBits = Src[i].SExtBits;
|
|
int64_t Scale = Src[i].Scale;
|
|
|
|
// Find V in Dest. This is N^2, but pointer indices almost never have more
|
|
// than a few variable indexes.
|
|
for (unsigned j = 0, e = Dest.size(); j != e; ++j) {
|
|
if (!isValueEqualInPotentialCycles(Dest[j].V, V) ||
|
|
Dest[j].ZExtBits != ZExtBits || Dest[j].SExtBits != SExtBits)
|
|
continue;
|
|
|
|
// If we found it, subtract off Scale V's from the entry in Dest. If it
|
|
// goes to zero, remove the entry.
|
|
if (Dest[j].Scale != Scale)
|
|
Dest[j].Scale -= Scale;
|
|
else
|
|
Dest.erase(Dest.begin() + j);
|
|
Scale = 0;
|
|
break;
|
|
}
|
|
|
|
// If we didn't consume this entry, add it to the end of the Dest list.
|
|
if (Scale) {
|
|
VariableGEPIndex Entry = {V, ZExtBits, SExtBits, -Scale};
|
|
Dest.push_back(Entry);
|
|
}
|
|
}
|
|
}
|
|
|
|
bool BasicAAResult::constantOffsetHeuristic(
|
|
const SmallVectorImpl<VariableGEPIndex> &VarIndices, uint64_t V1Size,
|
|
uint64_t V2Size, int64_t BaseOffset, AssumptionCache *AC,
|
|
DominatorTree *DT) {
|
|
if (VarIndices.size() != 2 || V1Size == MemoryLocation::UnknownSize ||
|
|
V2Size == MemoryLocation::UnknownSize)
|
|
return false;
|
|
|
|
const VariableGEPIndex &Var0 = VarIndices[0], &Var1 = VarIndices[1];
|
|
|
|
if (Var0.ZExtBits != Var1.ZExtBits || Var0.SExtBits != Var1.SExtBits ||
|
|
Var0.Scale != -Var1.Scale)
|
|
return false;
|
|
|
|
unsigned Width = Var1.V->getType()->getIntegerBitWidth();
|
|
|
|
// We'll strip off the Extensions of Var0 and Var1 and do another round
|
|
// of GetLinearExpression decomposition. In the example above, if Var0
|
|
// is zext(%x + 1) we should get V1 == %x and V1Offset == 1.
|
|
|
|
APInt V0Scale(Width, 0), V0Offset(Width, 0), V1Scale(Width, 0),
|
|
V1Offset(Width, 0);
|
|
bool NSW = true, NUW = true;
|
|
unsigned V0ZExtBits = 0, V0SExtBits = 0, V1ZExtBits = 0, V1SExtBits = 0;
|
|
const Value *V0 = GetLinearExpression(Var0.V, V0Scale, V0Offset, V0ZExtBits,
|
|
V0SExtBits, DL, 0, AC, DT, NSW, NUW);
|
|
NSW = true;
|
|
NUW = true;
|
|
const Value *V1 = GetLinearExpression(Var1.V, V1Scale, V1Offset, V1ZExtBits,
|
|
V1SExtBits, DL, 0, AC, DT, NSW, NUW);
|
|
|
|
if (V0Scale != V1Scale || V0ZExtBits != V1ZExtBits ||
|
|
V0SExtBits != V1SExtBits || !isValueEqualInPotentialCycles(V0, V1))
|
|
return false;
|
|
|
|
// We have a hit - Var0 and Var1 only differ by a constant offset!
|
|
|
|
// If we've been sext'ed then zext'd the maximum difference between Var0 and
|
|
// Var1 is possible to calculate, but we're just interested in the absolute
|
|
// minimum difference between the two. The minimum distance may occur due to
|
|
// wrapping; consider "add i3 %i, 5": if %i == 7 then 7 + 5 mod 8 == 4, and so
|
|
// the minimum distance between %i and %i + 5 is 3.
|
|
APInt MinDiff = V0Offset - V1Offset, Wrapped = -MinDiff;
|
|
MinDiff = APIntOps::umin(MinDiff, Wrapped);
|
|
uint64_t MinDiffBytes = MinDiff.getZExtValue() * std::abs(Var0.Scale);
|
|
|
|
// We can't definitely say whether GEP1 is before or after V2 due to wrapping
|
|
// arithmetic (i.e. for some values of GEP1 and V2 GEP1 < V2, and for other
|
|
// values GEP1 > V2). We'll therefore only declare NoAlias if both V1Size and
|
|
// V2Size can fit in the MinDiffBytes gap.
|
|
return V1Size + std::abs(BaseOffset) <= MinDiffBytes &&
|
|
V2Size + std::abs(BaseOffset) <= MinDiffBytes;
|
|
}
|
|
|
|
//===----------------------------------------------------------------------===//
|
|
// BasicAliasAnalysis Pass
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
AnalysisKey BasicAA::Key;
|
|
|
|
BasicAAResult BasicAA::run(Function &F, FunctionAnalysisManager &AM) {
|
|
return BasicAAResult(F.getParent()->getDataLayout(),
|
|
AM.getResult<TargetLibraryAnalysis>(F),
|
|
AM.getResult<AssumptionAnalysis>(F),
|
|
&AM.getResult<DominatorTreeAnalysis>(F),
|
|
AM.getCachedResult<LoopAnalysis>(F));
|
|
}
|
|
|
|
BasicAAWrapperPass::BasicAAWrapperPass() : FunctionPass(ID) {
|
|
initializeBasicAAWrapperPassPass(*PassRegistry::getPassRegistry());
|
|
}
|
|
|
|
char BasicAAWrapperPass::ID = 0;
|
|
|
|
void BasicAAWrapperPass::anchor() {}
|
|
|
|
INITIALIZE_PASS_BEGIN(BasicAAWrapperPass, "basicaa",
|
|
"Basic Alias Analysis (stateless AA impl)", true, true)
|
|
INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
|
|
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
|
|
INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
|
|
INITIALIZE_PASS_END(BasicAAWrapperPass, "basicaa",
|
|
"Basic Alias Analysis (stateless AA impl)", true, true)
|
|
|
|
FunctionPass *llvm::createBasicAAWrapperPass() {
|
|
return new BasicAAWrapperPass();
|
|
}
|
|
|
|
bool BasicAAWrapperPass::runOnFunction(Function &F) {
|
|
auto &ACT = getAnalysis<AssumptionCacheTracker>();
|
|
auto &TLIWP = getAnalysis<TargetLibraryInfoWrapperPass>();
|
|
auto &DTWP = getAnalysis<DominatorTreeWrapperPass>();
|
|
auto *LIWP = getAnalysisIfAvailable<LoopInfoWrapperPass>();
|
|
|
|
Result.reset(new BasicAAResult(F.getParent()->getDataLayout(), TLIWP.getTLI(),
|
|
ACT.getAssumptionCache(F), &DTWP.getDomTree(),
|
|
LIWP ? &LIWP->getLoopInfo() : nullptr));
|
|
|
|
return false;
|
|
}
|
|
|
|
void BasicAAWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const {
|
|
AU.setPreservesAll();
|
|
AU.addRequired<AssumptionCacheTracker>();
|
|
AU.addRequired<DominatorTreeWrapperPass>();
|
|
AU.addRequired<TargetLibraryInfoWrapperPass>();
|
|
}
|
|
|
|
BasicAAResult llvm::createLegacyPMBasicAAResult(Pass &P, Function &F) {
|
|
return BasicAAResult(
|
|
F.getParent()->getDataLayout(),
|
|
P.getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(),
|
|
P.getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F));
|
|
}
|