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llvm-project/llvm/lib/Target/ARM/ARMCodeGenPrepare.cpp

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//===----- ARMCodeGenPrepare.cpp ------------------------------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
/// \file
/// This pass inserts intrinsics to handle small types that would otherwise be
/// promoted during legalization. Here we can manually promote types or insert
/// intrinsics which can handle narrow types that aren't supported by the
/// register classes.
//
//===----------------------------------------------------------------------===//
#include "ARM.h"
#include "ARMSubtarget.h"
#include "ARMTargetMachine.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/TargetPassConfig.h"
#include "llvm/IR/Attributes.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/InstrTypes.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Intrinsics.h"
#include "llvm/IR/Type.h"
#include "llvm/IR/Value.h"
#include "llvm/IR/Verifier.h"
#include "llvm/Pass.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/CommandLine.h"
#define DEBUG_TYPE "arm-codegenprepare"
using namespace llvm;
static cl::opt<bool>
DisableCGP("arm-disable-cgp", cl::Hidden, cl::init(true),
cl::desc("Disable ARM specific CodeGenPrepare pass"));
static cl::opt<bool>
EnableDSP("arm-enable-scalar-dsp", cl::Hidden, cl::init(false),
cl::desc("Use DSP instructions for scalar operations"));
static cl::opt<bool>
EnableDSPWithImms("arm-enable-scalar-dsp-imms", cl::Hidden, cl::init(false),
cl::desc("Use DSP instructions for scalar operations\
with immediate operands"));
// The goal of this pass is to enable more efficient code generation for
// operations on narrow types (i.e. types with < 32-bits) and this is a
// motivating IR code example:
//
// define hidden i32 @cmp(i8 zeroext) {
// %2 = add i8 %0, -49
// %3 = icmp ult i8 %2, 3
// ..
// }
//
// The issue here is that i8 is type-legalized to i32 because i8 is not a
// legal type. Thus, arithmetic is done in integer-precision, but then the
// byte value is masked out as follows:
//
// t19: i32 = add t4, Constant:i32<-49>
// t24: i32 = and t19, Constant:i32<255>
//
// Consequently, we generate code like this:
//
// subs r0, #49
// uxtb r1, r0
// cmp r1, #3
//
// This shows that masking out the byte value results in generation of
// the UXTB instruction. This is not optimal as r0 already contains the byte
// value we need, and so instead we can just generate:
//
// sub.w r1, r0, #49
// cmp r1, #3
//
// We achieve this by type promoting the IR to i32 like so for this example:
//
// define i32 @cmp(i8 zeroext %c) {
// %0 = zext i8 %c to i32
// %c.off = add i32 %0, -49
// %1 = icmp ult i32 %c.off, 3
// ..
// }
//
// For this to be valid and legal, we need to prove that the i32 add is
// producing the same value as the i8 addition, and that e.g. no overflow
// happens.
//
// A brief sketch of the algorithm and some terminology.
// We pattern match interesting IR patterns:
// - which have "sources": instructions producing narrow values (i8, i16), and
// - they have "sinks": instructions consuming these narrow values.
//
// We collect all instruction connecting sources and sinks in a worklist, so
// that we can mutate these instruction and perform type promotion when it is
// legal to do so.
namespace {
class IRPromoter {
SmallPtrSet<Value*, 8> NewInsts;
SmallVector<Instruction*, 4> InstsToRemove;
DenseMap<Value*, Type*> TruncTysMap;
SmallPtrSet<Value*, 8> Promoted;
Module *M = nullptr;
LLVMContext &Ctx;
IntegerType *ExtTy = nullptr;
IntegerType *OrigTy = nullptr;
void PrepareConstants(SmallPtrSetImpl<Value*> &Visited,
SmallPtrSetImpl<Instruction*> &SafeToPromote);
void ExtendSources(SmallPtrSetImpl<Value*> &Sources);
void PromoteTree(SmallPtrSetImpl<Value*> &Visited,
SmallPtrSetImpl<Value*> &Sources,
SmallPtrSetImpl<Instruction*> &Sinks,
SmallPtrSetImpl<Instruction*> &SafeToPromote);
void TruncateSinks(SmallPtrSetImpl<Value*> &Sources,
SmallPtrSetImpl<Instruction*> &Sinks);
void Cleanup(SmallPtrSetImpl<Value*> &Visited);
public:
IRPromoter(Module *M) : M(M), Ctx(M->getContext()),
ExtTy(Type::getInt32Ty(Ctx)) { }
void Mutate(Type *OrigTy,
SmallPtrSetImpl<Value*> &Visited,
SmallPtrSetImpl<Value*> &Sources,
SmallPtrSetImpl<Instruction*> &Sinks,
SmallPtrSetImpl<Instruction*> &SafeToPromote);
};
class ARMCodeGenPrepare : public FunctionPass {
const ARMSubtarget *ST = nullptr;
IRPromoter *Promoter = nullptr;
std::set<Value*> AllVisited;
SmallPtrSet<Instruction*, 8> SafeToPromote;
bool isSafeOverflow(Instruction *I);
bool isSupportedValue(Value *V);
bool isLegalToPromote(Value *V);
bool TryToPromote(Value *V);
public:
static char ID;
static unsigned TypeSize;
Type *OrigTy = nullptr;
ARMCodeGenPrepare() : FunctionPass(ID) {}
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<TargetPassConfig>();
}
StringRef getPassName() const override { return "ARM IR optimizations"; }
bool doInitialization(Module &M) override;
bool runOnFunction(Function &F) override;
bool doFinalization(Module &M) override;
};
}
static bool generateSignBits(Value *V) {
if (!isa<Instruction>(V))
return false;
unsigned Opc = cast<Instruction>(V)->getOpcode();
return Opc == Instruction::AShr || Opc == Instruction::SDiv ||
Opc == Instruction::SRem;
}
static bool EqualTypeSize(Value *V) {
return V->getType()->getScalarSizeInBits() == ARMCodeGenPrepare::TypeSize;
}
static bool LessOrEqualTypeSize(Value *V) {
return V->getType()->getScalarSizeInBits() <= ARMCodeGenPrepare::TypeSize;
}
static bool GreaterThanTypeSize(Value *V) {
return V->getType()->getScalarSizeInBits() > ARMCodeGenPrepare::TypeSize;
}
/// Some instructions can use 8- and 16-bit operands, and we don't need to
/// promote anything larger. We disallow booleans to make life easier when
/// dealing with icmps but allow any other integer that is <= 16 bits. Void
/// types are accepted so we can handle switches.
static bool isSupportedType(Value *V) {
Type *Ty = V->getType();
// Allow voids and pointers, these won't be promoted.
if (Ty->isVoidTy() || Ty->isPointerTy())
return true;
if (auto *Ld = dyn_cast<LoadInst>(V))
Ty = cast<PointerType>(Ld->getPointerOperandType())->getElementType();
if (!isa<IntegerType>(Ty))
return false;
return LessOrEqualTypeSize(V);
}
/// Return true if the given value is a source in the use-def chain, producing
/// a narrow (i8, i16) value. These values will be zext to start the promotion
/// of the tree to i32. We guarantee that these won't populate the upper bits
/// of the register. ZExt on the loads will be free, and the same for call
/// return values because we only accept ones that guarantee a zeroext ret val.
/// Many arguments will have the zeroext attribute too, so those would be free
/// too.
static bool isSource(Value *V) {
if (!isa<IntegerType>(V->getType()))
return false;
// TODO Allow zext to be sources.
if (isa<Argument>(V))
return true;
else if (isa<LoadInst>(V))
return true;
else if (isa<BitCastInst>(V))
return true;
else if (auto *Call = dyn_cast<CallInst>(V))
return Call->hasRetAttr(Attribute::AttrKind::ZExt);
else if (auto *Trunc = dyn_cast<TruncInst>(V))
return EqualTypeSize(Trunc);
return false;
}
/// Return true if V will require any promoted values to be truncated for the
/// the IR to remain valid. We can't mutate the value type of these
/// instructions.
static bool isSink(Value *V) {
// TODO The truncate also isn't actually necessary because we would already
// proved that the data value is kept within the range of the original data
// type.
if (auto *Store = dyn_cast<StoreInst>(V))
return LessOrEqualTypeSize(Store->getValueOperand());
if (auto *Return = dyn_cast<ReturnInst>(V))
return LessOrEqualTypeSize(Return->getReturnValue());
if (auto *Trunc = dyn_cast<TruncInst>(V))
return EqualTypeSize(Trunc->getOperand(0));
if (auto *ZExt = dyn_cast<ZExtInst>(V))
return GreaterThanTypeSize(ZExt);
if (auto *ICmp = dyn_cast<ICmpInst>(V))
return ICmp->isSigned();
return isa<CallInst>(V);
}
/// Return whether the instruction can be promoted within any modifications to
/// its operands or result.
bool ARMCodeGenPrepare::isSafeOverflow(Instruction *I) {
// FIXME Do we need NSW too?
if (isa<OverflowingBinaryOperator>(I) && I->hasNoUnsignedWrap())
return true;
// We can support a, potentially, overflowing instruction (I) if:
// - It is only used by an unsigned icmp.
// - The icmp uses a constant.
// - The overflowing value (I) is decreasing, i.e would underflow - wrapping
// around zero to become a larger number than before.
// - The underflowing instruction (I) also uses a constant.
//
// We can then use the two constants to calculate whether the result would
// wrap in respect to itself in the original bitwidth. If it doesn't wrap,
// just underflows the range, the icmp would give the same result whether the
// result has been truncated or not. We calculate this by:
// - Zero extending both constants, if needed, to 32-bits.
// - Take the absolute value of I's constant, adding this to the icmp const.
// - Check that this value is not out of range for small type. If it is, it
// means that it has underflowed enough to wrap around the icmp constant.
//
// For example:
//
// %sub = sub i8 %a, 2
// %cmp = icmp ule i8 %sub, 254
//
// If %a = 0, %sub = -2 == FE == 254
// But if this is evalulated as a i32
// %sub = -2 == FF FF FF FE == 4294967294
// So the unsigned compares (i8 and i32) would not yield the same result.
//
// Another way to look at it is:
// %a - 2 <= 254
// %a + 2 <= 254 + 2
// %a <= 256
// And we can't represent 256 in the i8 format, so we don't support it.
//
// Whereas:
//
// %sub i8 %a, 1
// %cmp = icmp ule i8 %sub, 254
//
// If %a = 0, %sub = -1 == FF == 255
// As i32:
// %sub = -1 == FF FF FF FF == 4294967295
//
// In this case, the unsigned compare results would be the same and this
// would also be true for ult, uge and ugt:
// - (255 < 254) == (0xFFFFFFFF < 254) == false
// - (255 <= 254) == (0xFFFFFFFF <= 254) == false
// - (255 > 254) == (0xFFFFFFFF > 254) == true
// - (255 >= 254) == (0xFFFFFFFF >= 254) == true
//
// To demonstrate why we can't handle increasing values:
//
// %add = add i8 %a, 2
// %cmp = icmp ult i8 %add, 127
//
// If %a = 254, %add = 256 == (i8 1)
// As i32:
// %add = 256
//
// (1 < 127) != (256 < 127)
unsigned Opc = I->getOpcode();
if (Opc != Instruction::Add && Opc != Instruction::Sub)
return false;
if (!I->hasOneUse() ||
!isa<ICmpInst>(*I->user_begin()) ||
!isa<ConstantInt>(I->getOperand(1)))
return false;
ConstantInt *OverflowConst = cast<ConstantInt>(I->getOperand(1));
bool NegImm = OverflowConst->isNegative();
bool IsDecreasing = ((Opc == Instruction::Sub) && !NegImm) ||
((Opc == Instruction::Add) && NegImm);
if (!IsDecreasing)
return false;
// Don't support an icmp that deals with sign bits.
auto *CI = cast<ICmpInst>(*I->user_begin());
if (CI->isSigned() || CI->isEquality())
return false;
ConstantInt *ICmpConst = nullptr;
if (auto *Const = dyn_cast<ConstantInt>(CI->getOperand(0)))
ICmpConst = Const;
else if (auto *Const = dyn_cast<ConstantInt>(CI->getOperand(1)))
ICmpConst = Const;
else
return false;
// Now check that the result can't wrap on itself.
APInt Total = ICmpConst->getValue().getBitWidth() < 32 ?
ICmpConst->getValue().zext(32) : ICmpConst->getValue();
Total += OverflowConst->getValue().getBitWidth() < 32 ?
OverflowConst->getValue().abs().zext(32) : OverflowConst->getValue().abs();
APInt Max = APInt::getAllOnesValue(ARMCodeGenPrepare::TypeSize);
if (Total.getBitWidth() > Max.getBitWidth()) {
if (Total.ugt(Max.zext(Total.getBitWidth())))
return false;
} else if (Max.getBitWidth() > Total.getBitWidth()) {
if (Total.zext(Max.getBitWidth()).ugt(Max))
return false;
} else if (Total.ugt(Max))
return false;
LLVM_DEBUG(dbgs() << "ARM CGP: Allowing safe overflow for " << *I << "\n");
return true;
}
static bool shouldPromote(Value *V) {
if (!isa<IntegerType>(V->getType()) || isSink(V))
return false;
if (isSource(V))
return true;
auto *I = dyn_cast<Instruction>(V);
if (!I)
return false;
if (isa<ICmpInst>(I))
return false;
return true;
}
/// Return whether we can safely mutate V's type to ExtTy without having to be
/// concerned with zero extending or truncation.
static bool isPromotedResultSafe(Value *V) {
if (!isa<Instruction>(V))
return true;
if (generateSignBits(V))
return false;
return !isa<OverflowingBinaryOperator>(V);
}
/// Return the intrinsic for the instruction that can perform the same
/// operation but on a narrow type. This is using the parallel dsp intrinsics
/// on scalar values.
static Intrinsic::ID getNarrowIntrinsic(Instruction *I) {
// Whether we use the signed or unsigned versions of these intrinsics
// doesn't matter because we're not using the GE bits that they set in
// the APSR.
switch(I->getOpcode()) {
default:
break;
case Instruction::Add:
return ARMCodeGenPrepare::TypeSize == 16 ? Intrinsic::arm_uadd16 :
Intrinsic::arm_uadd8;
case Instruction::Sub:
return ARMCodeGenPrepare::TypeSize == 16 ? Intrinsic::arm_usub16 :
Intrinsic::arm_usub8;
}
llvm_unreachable("unhandled opcode for narrow intrinsic");
}
static void ReplaceAllUsersOfWith(Value *From, Value *To) {
SmallVector<Instruction*, 4> Users;
Instruction *InstTo = dyn_cast<Instruction>(To);
for (Use &U : From->uses()) {
auto *User = cast<Instruction>(U.getUser());
if (InstTo && User->isIdenticalTo(InstTo))
continue;
Users.push_back(User);
}
for (auto *U : Users)
U->replaceUsesOfWith(From, To);
}
void
IRPromoter::PrepareConstants(SmallPtrSetImpl<Value*> &Visited,
SmallPtrSetImpl<Instruction*> &SafeToPromote) {
IRBuilder<> Builder{Ctx};
// First step is to prepare the instructions for mutation. Most constants
// just need to be zero extended into their new type, but complications arise
// because:
// - For nuw binary operators, negative immediates would need sign extending;
// however, instead we'll change them to positive and zext them. We can do
// this because:
// > The operators that can wrap are: add, sub, mul and shl.
// > shl interprets its second operand as unsigned and if the first operand
// is an immediate, it will need zext to be nuw.
// > I'm assuming mul has to interpret immediates as unsigned for nuw.
// > Which leaves the nuw add and sub to be handled; as with shl, if an
// immediate is used as operand 0, it will need zext to be nuw.
// - We also allow add and sub to safely overflow in certain circumstances
// and only when the value (operand 0) is being decreased.
//
// For adds and subs, that are either nuw or safely wrap and use a negative
// immediate as operand 1, we create an equivalent instruction using a
// positive immediate. That positive immediate can then be zext along with
// all the other immediates later.
for (auto *V : Visited) {
if (!isa<Instruction>(V))
continue;
auto *I = cast<Instruction>(V);
if (SafeToPromote.count(I)) {
if (!isa<OverflowingBinaryOperator>(I))
continue;
if (auto *Const = dyn_cast<ConstantInt>(I->getOperand(1))) {
if (!Const->isNegative())
break;
unsigned Opc = I->getOpcode();
if (Opc != Instruction::Add && Opc != Instruction::Sub)
continue;
LLVM_DEBUG(dbgs() << "ARM CGP: Adjusting " << *I << "\n");
auto *NewConst = ConstantInt::get(Ctx, Const->getValue().abs());
Builder.SetInsertPoint(I);
Value *NewVal = Opc == Instruction::Sub ?
Builder.CreateAdd(I->getOperand(0), NewConst) :
Builder.CreateSub(I->getOperand(0), NewConst);
LLVM_DEBUG(dbgs() << "ARM CGP: New equivalent: " << *NewVal << "\n");
if (auto *NewInst = dyn_cast<Instruction>(NewVal)) {
NewInst->copyIRFlags(I);
NewInsts.insert(NewInst);
}
InstsToRemove.push_back(I);
I->replaceAllUsesWith(NewVal);
}
}
}
for (auto *I : NewInsts)
Visited.insert(I);
}
void IRPromoter::ExtendSources(SmallPtrSetImpl<Value*> &Sources) {
IRBuilder<> Builder{Ctx};
auto InsertZExt = [&](Value *V, Instruction *InsertPt) {
assert(V->getType() != ExtTy && "zext already extends to i32");
LLVM_DEBUG(dbgs() << "ARM CGP: Inserting ZExt for " << *V << "\n");
Builder.SetInsertPoint(InsertPt);
if (auto *I = dyn_cast<Instruction>(V))
Builder.SetCurrentDebugLocation(I->getDebugLoc());
Value *ZExt = Builder.CreateZExt(V, ExtTy);
if (auto *I = dyn_cast<Instruction>(ZExt)) {
if (isa<Argument>(V))
I->moveBefore(InsertPt);
else
I->moveAfter(InsertPt);
NewInsts.insert(I);
}
ReplaceAllUsersOfWith(V, ZExt);
TruncTysMap[ZExt] = TruncTysMap[V];
};
// Now, insert extending instructions between the sources and their users.
LLVM_DEBUG(dbgs() << "ARM CGP: Promoting sources:\n");
for (auto V : Sources) {
LLVM_DEBUG(dbgs() << " - " << *V << "\n");
if (auto *I = dyn_cast<Instruction>(V))
InsertZExt(I, I);
else if (auto *Arg = dyn_cast<Argument>(V)) {
BasicBlock &BB = Arg->getParent()->front();
InsertZExt(Arg, &*BB.getFirstInsertionPt());
} else {
llvm_unreachable("unhandled source that needs extending");
}
Promoted.insert(V);
}
}
void IRPromoter::PromoteTree(SmallPtrSetImpl<Value*> &Visited,
SmallPtrSetImpl<Value*> &Sources,
SmallPtrSetImpl<Instruction*> &Sinks,
SmallPtrSetImpl<Instruction*> &SafeToPromote) {
LLVM_DEBUG(dbgs() << "ARM CGP: Mutating the tree..\n");
IRBuilder<> Builder{Ctx};
// Mutate the types of the instructions within the tree. Here we handle
// constant operands.
for (auto *V : Visited) {
if (Sources.count(V))
continue;
auto *I = cast<Instruction>(V);
if (Sinks.count(I))
continue;
for (unsigned i = 0, e = I->getNumOperands(); i < e; ++i) {
Value *Op = I->getOperand(i);
if ((Op->getType() == ExtTy) || !isa<IntegerType>(Op->getType()))
continue;
if (auto *Const = dyn_cast<ConstantInt>(Op)) {
Constant *NewConst = ConstantExpr::getZExt(Const, ExtTy);
I->setOperand(i, NewConst);
} else if (isa<UndefValue>(Op))
I->setOperand(i, UndefValue::get(ExtTy));
}
if (shouldPromote(I)) {
I->mutateType(ExtTy);
Promoted.insert(I);
}
}
// Finally, any instructions that should be promoted but haven't yet been,
// need to be handled using intrinsics.
for (auto *V : Visited) {
auto *I = dyn_cast<Instruction>(V);
if (!I)
continue;
if (Sources.count(I) || Sinks.count(I))
continue;
if (!shouldPromote(I) || SafeToPromote.count(I) || NewInsts.count(I))
continue;
assert(EnableDSP && "DSP intrinisc insertion not enabled!");
// Replace unsafe instructions with appropriate intrinsic calls.
LLVM_DEBUG(dbgs() << "ARM CGP: Inserting DSP intrinsic for "
<< *I << "\n");
Function *DSPInst =
Intrinsic::getDeclaration(M, getNarrowIntrinsic(I));
Builder.SetInsertPoint(I);
Builder.SetCurrentDebugLocation(I->getDebugLoc());
Value *Args[] = { I->getOperand(0), I->getOperand(1) };
CallInst *Call = Builder.CreateCall(DSPInst, Args);
ReplaceAllUsersOfWith(I, Call);
InstsToRemove.push_back(I);
NewInsts.insert(Call);
TruncTysMap[Call] = OrigTy;
}
}
void IRPromoter::TruncateSinks(SmallPtrSetImpl<Value*> &Sources,
SmallPtrSetImpl<Instruction*> &Sinks) {
LLVM_DEBUG(dbgs() << "ARM CGP: Fixing up the sinks:\n");
IRBuilder<> Builder{Ctx};
auto InsertTrunc = [&](Value *V) -> Instruction* {
if (!isa<Instruction>(V) || !isa<IntegerType>(V->getType()))
return nullptr;
if ((!Promoted.count(V) && !NewInsts.count(V)) || !TruncTysMap.count(V) ||
Sources.count(V))
return nullptr;
Type *TruncTy = TruncTysMap[V];
if (TruncTy == ExtTy)
return nullptr;
LLVM_DEBUG(dbgs() << "ARM CGP: Creating " << *TruncTy << " Trunc for "
<< *V << "\n");
Builder.SetInsertPoint(cast<Instruction>(V));
auto *Trunc = dyn_cast<Instruction>(Builder.CreateTrunc(V, TruncTy));
if (Trunc)
NewInsts.insert(Trunc);
return Trunc;
};
// Fix up any stores or returns that use the results of the promoted
// chain.
for (auto I : Sinks) {
LLVM_DEBUG(dbgs() << " - " << *I << "\n");
// Handle calls separately as we need to iterate over arg operands.
if (auto *Call = dyn_cast<CallInst>(I)) {
for (unsigned i = 0; i < Call->getNumArgOperands(); ++i) {
Value *Arg = Call->getArgOperand(i);
if (Instruction *Trunc = InsertTrunc(Arg)) {
Trunc->moveBefore(Call);
Call->setArgOperand(i, Trunc);
}
}
continue;
}
// Now handle the others.
for (unsigned i = 0; i < I->getNumOperands(); ++i) {
if (Instruction *Trunc = InsertTrunc(I->getOperand(i))) {
Trunc->moveBefore(I);
I->setOperand(i, Trunc);
}
}
}
}
void IRPromoter::Cleanup(SmallPtrSetImpl<Value*> &Visited) {
// Some zexts will now have become redundant, along with their trunc
// operands, so remove them
for (auto V : Visited) {
if (!isa<ZExtInst>(V))
continue;
auto ZExt = cast<ZExtInst>(V);
if (ZExt->getDestTy() != ExtTy)
continue;
Value *Src = ZExt->getOperand(0);
if (ZExt->getSrcTy() == ZExt->getDestTy()) {
LLVM_DEBUG(dbgs() << "ARM CGP: Removing unnecessary cast.\n");
ReplaceAllUsersOfWith(ZExt, Src);
InstsToRemove.push_back(ZExt);
continue;
}
// For any truncs that we insert to handle zexts, we can replace the
// result of the zext with the input to the trunc.
if (NewInsts.count(Src) && isa<TruncInst>(Src)) {
auto *Trunc = cast<TruncInst>(Src);
assert(Trunc->getOperand(0)->getType() == ExtTy &&
"expected inserted trunc to be operating on i32");
LLVM_DEBUG(dbgs() << "ARM CGP: Replacing zext with trunc operand: "
<< *Trunc->getOperand(0));
ReplaceAllUsersOfWith(ZExt, Trunc->getOperand(0));
InstsToRemove.push_back(ZExt);
}
}
for (auto *I : InstsToRemove) {
LLVM_DEBUG(dbgs() << "ARM CGP: Removing " << *I << "\n");
I->dropAllReferences();
I->eraseFromParent();
}
InstsToRemove.clear();
NewInsts.clear();
TruncTysMap.clear();
Promoted.clear();
}
void IRPromoter::Mutate(Type *OrigTy,
SmallPtrSetImpl<Value*> &Visited,
SmallPtrSetImpl<Value*> &Sources,
SmallPtrSetImpl<Instruction*> &Sinks,
SmallPtrSetImpl<Instruction*> &SafeToPromote) {
LLVM_DEBUG(dbgs() << "ARM CGP: Promoting use-def chains to from "
<< ARMCodeGenPrepare::TypeSize << " to 32-bits\n");
assert(isa<IntegerType>(OrigTy) && "expected integer type");
this->OrigTy = cast<IntegerType>(OrigTy);
assert(OrigTy->getPrimitiveSizeInBits() < ExtTy->getPrimitiveSizeInBits() &&
"original type not smaller than extended type");
// Cache original types.
for (auto *V : Visited)
TruncTysMap[V] = V->getType();
// Convert adds and subs using negative immediates to equivalent instructions
// that use positive constants.
PrepareConstants(Visited, SafeToPromote);
// Insert zext instructions between sources and their users.
ExtendSources(Sources);
// Promote visited instructions, mutating their types in place. Also insert
// DSP intrinsics, if enabled, for adds and subs which would be unsafe to
// promote.
PromoteTree(Visited, Sources, Sinks, SafeToPromote);
// Insert trunc instructions for use by calls, stores etc...
TruncateSinks(Sources, Sinks);
// Finally, remove unecessary zexts and truncs, delete old instructions and
// clear the data structures.
Cleanup(Visited);
LLVM_DEBUG(dbgs() << "ARM CGP: Mutation complete\n");
}
/// We accept most instructions, as well as Arguments and ConstantInsts. We
/// Disallow casts other than zext and truncs and only allow calls if their
/// return value is zeroext. We don't allow opcodes that can introduce sign
/// bits.
bool ARMCodeGenPrepare::isSupportedValue(Value *V) {
if (auto *I = dyn_cast<ICmpInst>(V)) {
// Now that we allow small types than TypeSize, only allow icmp of
// TypeSize because they will require a trunc to be legalised.
// TODO: Allow icmp of smaller types, and calculate at the end
// whether the transform would be beneficial.
if (isa<PointerType>(I->getOperand(0)->getType()))
return true;
return EqualTypeSize(I->getOperand(0));
}
// Memory instructions
if (isa<StoreInst>(V) || isa<GetElementPtrInst>(V))
return true;
// Branches and targets.
if( isa<BranchInst>(V) || isa<SwitchInst>(V) || isa<BasicBlock>(V))
return true;
// Non-instruction values that we can handle.
if ((isa<Constant>(V) && !isa<ConstantExpr>(V)) || isa<Argument>(V))
return isSupportedType(V);
if (isa<PHINode>(V) || isa<SelectInst>(V) || isa<ReturnInst>(V) ||
isa<LoadInst>(V))
return isSupportedType(V);
if (isa<SExtInst>(V))
return false;
if (auto *Cast = dyn_cast<CastInst>(V))
return isSupportedType(Cast) || isSupportedType(Cast->getOperand(0));
// Special cases for calls as we need to check for zeroext
// TODO We should accept calls even if they don't have zeroext, as they can
// still be sinks.
if (auto *Call = dyn_cast<CallInst>(V))
return isSupportedType(Call) &&
Call->hasRetAttr(Attribute::AttrKind::ZExt);
if (!isa<BinaryOperator>(V))
return false;
if (!isSupportedType(V))
return false;
if (generateSignBits(V)) {
LLVM_DEBUG(dbgs() << "ARM CGP: No, instruction can generate sign bits.\n");
return false;
}
return true;
}
/// Check that the type of V would be promoted and that the original type is
/// smaller than the targeted promoted type. Check that we're not trying to
/// promote something larger than our base 'TypeSize' type.
bool ARMCodeGenPrepare::isLegalToPromote(Value *V) {
auto *I = dyn_cast<Instruction>(V);
if (!I)
return true;
if (SafeToPromote.count(I))
return true;
if (isPromotedResultSafe(V) || isSafeOverflow(I)) {
SafeToPromote.insert(I);
return true;
}
if (I->getOpcode() != Instruction::Add && I->getOpcode() != Instruction::Sub)
return false;
// If promotion is not safe, can we use a DSP instruction to natively
// handle the narrow type?
if (!ST->hasDSP() || !EnableDSP || !isSupportedType(I))
return false;
if (ST->isThumb() && !ST->hasThumb2())
return false;
// TODO
// Would it be profitable? For Thumb code, these parallel DSP instructions
// are only Thumb-2, so we wouldn't be able to dual issue on Cortex-M33. For
// Cortex-A, specifically Cortex-A72, the latency is double and throughput is
// halved. They also do not take immediates as operands.
for (auto &Op : I->operands()) {
if (isa<Constant>(Op)) {
if (!EnableDSPWithImms)
return false;
}
}
LLVM_DEBUG(dbgs() << "ARM CGP: Will use an intrinsic for: " << *I << "\n");
return true;
}
bool ARMCodeGenPrepare::TryToPromote(Value *V) {
OrigTy = V->getType();
TypeSize = OrigTy->getPrimitiveSizeInBits();
if (TypeSize > 16 || TypeSize < 8)
return false;
SafeToPromote.clear();
if (!isSupportedValue(V) || !shouldPromote(V) || !isLegalToPromote(V))
return false;
LLVM_DEBUG(dbgs() << "ARM CGP: TryToPromote: " << *V << ", TypeSize = "
<< TypeSize << "\n");
SetVector<Value*> WorkList;
SmallPtrSet<Value*, 8> Sources;
SmallPtrSet<Instruction*, 4> Sinks;
SmallPtrSet<Value*, 16> CurrentVisited;
WorkList.insert(V);
// Return true if V was added to the worklist as a supported instruction,
// if it was already visited, or if we don't need to explore it (e.g.
// pointer values and GEPs), and false otherwise.
auto AddLegalInst = [&](Value *V) {
if (CurrentVisited.count(V))
return true;
// Ignore GEPs because they don't need promoting and the constant indices
// will prevent the transformation.
if (isa<GetElementPtrInst>(V))
return true;
if (!isSupportedValue(V) || (shouldPromote(V) && !isLegalToPromote(V))) {
LLVM_DEBUG(dbgs() << "ARM CGP: Can't handle: " << *V << "\n");
return false;
}
WorkList.insert(V);
return true;
};
// Iterate through, and add to, a tree of operands and users in the use-def.
while (!WorkList.empty()) {
Value *V = WorkList.back();
WorkList.pop_back();
if (CurrentVisited.count(V))
continue;
// Ignore non-instructions, other than arguments.
if (!isa<Instruction>(V) && !isSource(V))
continue;
// If we've already visited this value from somewhere, bail now because
// the tree has already been explored.
// TODO: This could limit the transform, ie if we try to promote something
// from an i8 and fail first, before trying an i16.
if (AllVisited.count(V))
return false;
CurrentVisited.insert(V);
AllVisited.insert(V);
// Calls can be both sources and sinks.
if (isSink(V))
Sinks.insert(cast<Instruction>(V));
if (isSource(V))
Sources.insert(V);
if (!isSink(V) && !isSource(V)) {
if (auto *I = dyn_cast<Instruction>(V)) {
// Visit operands of any instruction visited.
for (auto &U : I->operands()) {
if (!AddLegalInst(U))
return false;
}
}
}
// Don't visit users of a node which isn't going to be mutated unless its a
// source.
if (isSource(V) || shouldPromote(V)) {
for (Use &U : V->uses()) {
if (!AddLegalInst(U.getUser()))
return false;
}
}
}
LLVM_DEBUG(dbgs() << "ARM CGP: Visited nodes:\n";
for (auto *I : CurrentVisited)
I->dump();
);
unsigned ToPromote = 0;
for (auto *V : CurrentVisited) {
if (Sources.count(V))
continue;
if (Sinks.count(cast<Instruction>(V)))
continue;
++ToPromote;
}
if (ToPromote < 2)
return false;
Promoter->Mutate(OrigTy, CurrentVisited, Sources, Sinks, SafeToPromote);
return true;
}
bool ARMCodeGenPrepare::doInitialization(Module &M) {
Promoter = new IRPromoter(&M);
return false;
}
bool ARMCodeGenPrepare::runOnFunction(Function &F) {
if (skipFunction(F) || DisableCGP)
return false;
auto *TPC = &getAnalysis<TargetPassConfig>();
if (!TPC)
return false;
const TargetMachine &TM = TPC->getTM<TargetMachine>();
ST = &TM.getSubtarget<ARMSubtarget>(F);
bool MadeChange = false;
LLVM_DEBUG(dbgs() << "ARM CGP: Running on " << F.getName() << "\n");
// Search up from icmps to try to promote their operands.
for (BasicBlock &BB : F) {
auto &Insts = BB.getInstList();
for (auto &I : Insts) {
if (AllVisited.count(&I))
continue;
if (isa<ICmpInst>(I)) {
auto &CI = cast<ICmpInst>(I);
// Skip signed or pointer compares
if (CI.isSigned() || !isa<IntegerType>(CI.getOperand(0)->getType()))
continue;
LLVM_DEBUG(dbgs() << "ARM CGP: Searching from: " << CI << "\n");
for (auto &Op : CI.operands()) {
if (auto *I = dyn_cast<Instruction>(Op))
MadeChange |= TryToPromote(I);
}
}
}
LLVM_DEBUG(if (verifyFunction(F, &dbgs())) {
dbgs() << F;
report_fatal_error("Broken function after type promotion");
});
}
if (MadeChange)
LLVM_DEBUG(dbgs() << "After ARMCodeGenPrepare: " << F << "\n");
return MadeChange;
}
bool ARMCodeGenPrepare::doFinalization(Module &M) {
delete Promoter;
return false;
}
INITIALIZE_PASS_BEGIN(ARMCodeGenPrepare, DEBUG_TYPE,
"ARM IR optimizations", false, false)
INITIALIZE_PASS_END(ARMCodeGenPrepare, DEBUG_TYPE, "ARM IR optimizations",
false, false)
char ARMCodeGenPrepare::ID = 0;
unsigned ARMCodeGenPrepare::TypeSize = 0;
FunctionPass *llvm::createARMCodeGenPreparePass() {
return new ARMCodeGenPrepare();
}
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