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Revert "Remove an InstCombine that seems to have become redundant."

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Assertion fires in compiler-rt. Guess it does fire..

This reverts commit r233116.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@233121 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
David Blaikie 2015-03-24 21:50:35 +00:00
parent 45eaa023df
commit ef9962d9bb
2 changed files with 29 additions and 20 deletions
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41
lib/Transforms/InstCombine/InstCombineCasts.cpp
View File

@ -1455,20 +1455,35 @@ Instruction *InstCombiner::commonPointerCastTransforms(CastInst &CI) {
// GEP computes a constant offset, see if we can convert these three
// instructions into fewer. This typically happens with unions and other
// non-type-safe code.
// Looks like this never actually fires due to bitcast+gep folding happening
// in InstCombiner::visitGetElementPtrInst where the bitcast operand to a
// gep is folded into the gep if possible, before we consider whether that
// gep is used in a bitcast as well.
// Let's assert that this wouldn't fire just to be sure.
#ifndef NDEBUG
APInt Offset(DL.getPointerSizeInBits(GEP->getPointerAddressSpace()), 0);
unsigned AS = GEP->getPointerAddressSpace();
unsigned OffsetBits = DL.getPointerSizeInBits(AS);
APInt Offset(OffsetBits, 0);
BitCastInst *BCI = dyn_cast<BitCastInst>(GEP->getOperand(0));
SmallVector<Value *, 8> NewIndices;
assert(!BCI || !GEP->hasOneUse() ||
!GEP->accumulateConstantOffset(DL, Offset) ||
!FindElementAtOffset(BCI->getOperand(0)->getType(),
Offset.getSExtValue(), NewIndices));
#endif
if (GEP->hasOneUse() && BCI && GEP->accumulateConstantOffset(DL, Offset)) {
// FIXME: This is insufficiently tested - just a no-crash test
// (test/Transforms/InstCombine/2007-05-14-Crash.ll)
//
// Get the base pointer input of the bitcast, and the type it points to.
Value *OrigBase = BCI->getOperand(0);
SmallVector<Value*, 8> NewIndices;
if (FindElementAtOffset(OrigBase->getType(), Offset.getSExtValue(),
NewIndices)) {
// FIXME: This codepath is completely untested - could be unreachable
// for all I know.
// If we were able to index down into an element, create the GEP
// and bitcast the result. This eliminates one bitcast, potentially
// two.
Value *NGEP = cast<GEPOperator>(GEP)->isInBounds() ?
Builder->CreateInBoundsGEP(OrigBase, NewIndices) :
Builder->CreateGEP(OrigBase, NewIndices);
NGEP->takeName(GEP);
if (isa<BitCastInst>(CI))
return new BitCastInst(NGEP, CI.getType());
assert(isa<PtrToIntInst>(CI));
return new PtrToIntInst(NGEP, CI.getType());
}
}
}
return commonCastTransforms(CI);

8
test/Transforms/InstCombine/2007-05-14-Crash.ll
View File

@ -15,10 +15,4 @@ entry:
ret i8* %tmp35
}
define i32* @bar(%struct.abc* %abc) {
entry:
%tmp1 = bitcast %struct.abc* %abc to %struct.def*
%tmp3 = getelementptr %struct.def, %struct.def* %tmp1, i32 0, i32 1
%tmp35 = bitcast %struct.abc* %tmp3 to i32*
ret i32* %tmp35
}