[Analysis] Centralize objectsize lowering logic.

We're currently doing nearly the same thing for @llvm.objectsize in
three different places: two of them are missing checks for overflow,
and one of them could subtly break if InstCombine gets much smarter
about removing alloc sites. Seems like a good idea to not do that.

llvm-svn: 290214
This commit is contained in:
George Burgess IV 2016-12-20 23:46:36 +00:00
parent e52614b5c7
commit 3f08914e7e
6 changed files with 84 additions and 29 deletions

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@ -141,6 +141,16 @@ bool getObjectSize(const Value *Ptr, uint64_t &Size, const DataLayout &DL,
const TargetLibraryInfo *TLI, bool RoundToAlign = false,
ObjSizeMode Mode = ObjSizeMode::Exact);
/// Try to turn a call to @llvm.objectsize into an integer value of the given
/// Type. Returns null on failure.
/// If MustSucceed is true, this function will not return null, and may return
/// conservative values governed by the second argument of the call to
/// objectsize.
ConstantInt *lowerObjectSizeCall(IntrinsicInst *ObjectSize,
const DataLayout &DL,
const TargetLibraryInfo *TLI,
bool MustSucceed);
typedef std::pair<APInt, APInt> SizeOffsetType;
/// \brief Evaluate the size and offset of an object pointed to by a Value*

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@ -388,6 +388,36 @@ bool llvm::getObjectSize(const Value *Ptr, uint64_t &Size, const DataLayout &DL,
return true;
}
ConstantInt *llvm::lowerObjectSizeCall(IntrinsicInst *ObjectSize,
const DataLayout &DL,
const TargetLibraryInfo *TLI,
bool MustSucceed) {
assert(ObjectSize->getIntrinsicID() == Intrinsic::objectsize &&
"ObjectSize must be a call to llvm.objectsize!");
bool MaxVal = cast<ConstantInt>(ObjectSize->getArgOperand(1))->isZero();
ObjSizeMode Mode;
// Unless we have to fold this to something, try to be as accurate as
// possible.
if (MustSucceed)
Mode = MaxVal ? ObjSizeMode::Max : ObjSizeMode::Min;
else
Mode = ObjSizeMode::Exact;
// FIXME: Does it make sense to just return a failure value if the size won't
// fit in the output and `!MustSucceed`?
uint64_t Size;
auto *ResultType = cast<IntegerType>(ObjectSize->getType());
if (getObjectSize(ObjectSize->getArgOperand(0), Size, DL, TLI, false, Mode) &&
isUIntN(ResultType->getBitWidth(), Size))
return ConstantInt::get(ResultType, Size);
if (!MustSucceed)
return nullptr;
return ConstantInt::get(ResultType, MaxVal ? -1ULL : 0);
}
STATISTIC(ObjectVisitorArgument,
"Number of arguments with unsolved size and offset");
STATISTIC(ObjectVisitorLoad,

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@ -1948,18 +1948,8 @@ bool CodeGenPrepare::optimizeCallInst(CallInst *CI, bool& ModifiedDT) {
default: break;
case Intrinsic::objectsize: {
// Lower all uses of llvm.objectsize.*
uint64_t Size;
Type *ReturnTy = CI->getType();
Constant *RetVal = nullptr;
ConstantInt *Op1 = cast<ConstantInt>(II->getArgOperand(1));
ObjSizeMode Mode = Op1->isZero() ? ObjSizeMode::Max : ObjSizeMode::Min;
if (getObjectSize(II->getArgOperand(0),
Size, *DL, TLInfo, false, Mode)) {
RetVal = ConstantInt::get(ReturnTy, Size);
} else {
RetVal = ConstantInt::get(ReturnTy,
Mode == ObjSizeMode::Min ? 0 : -1ULL);
}
ConstantInt *RetVal =
lowerObjectSizeCall(II, *DL, TLInfo, /*MustSucceed=*/true);
// Substituting this can cause recursive simplifications, which can
// invalidate our iterator. Use a WeakVH to hold onto it in case this
// happens.

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@ -1440,17 +1440,12 @@ Instruction *InstCombiner::visitCallInst(CallInst &CI) {
switch (II->getIntrinsicID()) {
default: break;
case Intrinsic::objectsize: {
uint64_t Size;
if (getObjectSize(II->getArgOperand(0), Size, DL, &TLI)) {
APInt APSize(II->getType()->getIntegerBitWidth(), Size);
// Equality check to be sure that `Size` can fit in a value of type
// `II->getType()`
if (APSize == Size)
return replaceInstUsesWith(CI, ConstantInt::get(II->getType(), APSize));
}
case Intrinsic::objectsize:
if (ConstantInt *N =
lowerObjectSizeCall(II, DL, &TLI, /*MustSucceed=*/false))
return replaceInstUsesWith(CI, N);
return nullptr;
}
case Intrinsic::bswap: {
Value *IIOperand = II->getArgOperand(0);
Value *X = nullptr;

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@ -2027,12 +2027,9 @@ Instruction *InstCombiner::visitAllocSite(Instruction &MI) {
if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
if (II->getIntrinsicID() == Intrinsic::objectsize) {
uint64_t Size;
if (!getObjectSize(II->getArgOperand(0), Size, DL, &TLI)) {
ConstantInt *CI = cast<ConstantInt>(II->getArgOperand(1));
Size = CI->isZero() ? -1ULL : 0;
}
replaceInstUsesWith(*I, ConstantInt::get(I->getType(), Size));
ConstantInt *Result = lowerObjectSizeCall(II, DL, &TLI,
/*MustSucceed=*/true);
replaceInstUsesWith(*I, Result);
eraseInstFromFunction(*I);
Users[i] = nullptr; // Skip examining in the next loop.
}

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@ -1,5 +1,38 @@
; RUN: opt -codegenprepare -S < %s | FileCheck %s
; Ensure we act sanely on overflow.
; CHECK-LABEL: define i32 @bar
define i32 @bar() {
entry:
; CHECK: ret i32 -1
%az = alloca [2147483649 x i32], align 16
%a = alloca i8*, align 8
%arraydecay = getelementptr inbounds [2147483649 x i32], [2147483649 x i32]* %az, i32 0, i32 0
%0 = bitcast i32* %arraydecay to i8*
store i8* %0, i8** %a, align 8
%1 = load i8*, i8** %a, align 8
%2 = call i32 @llvm.objectsize.i32.p0i8(i8* %1, i1 false)
ret i32 %2
}
; CHECK-LABEL: define i32 @baz
define i32 @baz(i32 %n) {
entry:
; CHECK: ret i32 -1
%az = alloca [1 x i32], align 16
%bz = alloca [4294967297 x i32], align 16
%tobool = icmp ne i32 %n, 0
%arraydecay = getelementptr inbounds [1 x i32], [1 x i32]* %az, i64 0, i64 0
%arraydecay1 = getelementptr inbounds [4294967297 x i32], [4294967297 x i32]* %bz, i64 0, i64 0
%cond = select i1 %tobool, i32* %arraydecay, i32* %arraydecay1
%0 = bitcast i32* %cond to i8*
%1 = call i32 @llvm.objectsize.i32.p0i8(i8* %0, i1 false)
ret i32 %1
}
declare i32 @llvm.objectsize.i32.p0i8(i8*, i1)
; The following tests were generated by:
; #include<stdlib.h>
; #define STATIC_BUF_SIZE 10
; #define LARGER_BUF_SIZE 30