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[IRBuilder] Remove positivity check from CreateAlignmentAssumption() 

Summary:
An alignment should be non-zero positive power-of-two, anything and everything else is UB.
We should not have that check for all these prerequisites here, it's just UB.
Also, that was likely confusing middle-end passes.

While there, `CreateIntCast()` should be called with `/*isSigned*/ false`.
Think about it, there are two explanations: "An alignment should be positive",
therefore the sign bit is unset, so `zext` and `sext` is equivalent.
Or a second one: you have `i2 0b10` - a valid alignment,
now you `sext` it: `i2 0b110` - no longer valid alignment.

Reviewers: craig.topper, jyknight, hfinkel, erichkeane, rjmccall

Reviewed By: hfinkel, rjmccall

Subscribers: hfinkel, llvm-commits

Differential Revision: https://reviews.llvm.org/D54653

llvm-svn: 352089
This commit is contained in:
Roman Lebedev 2019-01-24 19:32:48 +00:00
parent 1ec465dbfd
commit a95a7105ef
1 changed files with 5 additions and 9 deletions
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14
llvm/include/llvm/IR/IRBuilder.h
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@ -2279,10 +2279,11 @@ public:
Value **TheCheck = nullptr) {
assert(isa<PointerType>(PtrValue->getType()) &&
"trying to create an alignment assumption on a non-pointer?");
assert(Alignment != 0 && "Invalid Alignment");
auto *PtrTy = cast<PointerType>(PtrValue->getType());
Type *IntPtrTy = getIntPtrTy(DL, PtrTy->getAddressSpace());
Value *Mask = ConstantInt::get(IntPtrTy, Alignment > 0 ? Alignment - 1 : 0);
Value *Mask = ConstantInt::get(IntPtrTy, Alignment - 1);
return CreateAlignmentAssumptionHelper(DL, PtrValue, Mask, IntPtrTy,
OffsetValue, TheCheck);
}
@ -2309,15 +2310,10 @@ public:
Type *IntPtrTy = getIntPtrTy(DL, PtrTy->getAddressSpace());
if (Alignment->getType() != IntPtrTy)
Alignment = CreateIntCast(Alignment, IntPtrTy, /*isSigned*/ true,
Alignment = CreateIntCast(Alignment, IntPtrTy, /*isSigned*/ false,
"alignmentcast");
Value *IsPositive =
CreateICmp(CmpInst::ICMP_SGT, Alignment,
ConstantInt::get(Alignment->getType(), 0), "ispositive");
Value *PositiveMask =
CreateSub(Alignment, ConstantInt::get(IntPtrTy, 1), "positivemask");
Value *Mask = CreateSelect(IsPositive, PositiveMask,
ConstantInt::get(IntPtrTy, 0), "mask");
Value *Mask = CreateSub(Alignment, ConstantInt::get(IntPtrTy, 1), "mask");
return CreateAlignmentAssumptionHelper(DL, PtrValue, Mask, IntPtrTy,
OffsetValue, TheCheck);