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Get rid of the getPointeeAlignment helper function from

Browse Source 
InstCombineLoadStoreAlloca.cpp, which had many issues.
(At least two bugs were noted on llvm-commits, and it was overly conservative.)
Instead, use getOrEnforceKnownAlignment.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@168629 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Eli Friedman 2012-11-26 23:04:53 +00:00
parent 1243922fc1
commit 0c617e6026
2 changed files with 14 additions and 22 deletions
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26
lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
View File

@ -150,26 +150,6 @@ isOnlyCopiedFromConstantGlobal(AllocaInst *AI,
return 0;
}
/// getPointeeAlignment - Compute the minimum alignment of the value pointed
/// to by the given pointer.
static unsigned getPointeeAlignment(Value *V, const DataLayout &TD) {
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V))
if (CE->getOpcode() == Instruction::BitCast ||
(CE->getOpcode() == Instruction::GetElementPtr &&
cast<GEPOperator>(CE)->hasAllZeroIndices()))
return getPointeeAlignment(CE->getOperand(0), TD);
if (GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
if (!GV->isDeclaration())
return TD.getPreferredAlignment(GV);
if (PointerType *PT = dyn_cast<PointerType>(V->getType()))
if (PT->getElementType()->isSized())
return TD.getABITypeAlignment(PT->getElementType());
return 0;
}
Instruction *InstCombiner::visitAllocaInst(AllocaInst &AI) {
// Ensure that the alloca array size argument has type intptr_t, so that
// any casting is exposed early.
@ -265,7 +245,7 @@ Instruction *InstCombiner::visitAllocaInst(AllocaInst &AI) {
}
}
if (TD) {
if (AI.getAlignment()) {
// Check to see if this allocation is only modified by a memcpy/memmove from
// a constant global whose alignment is equal to or exceeds that of the
// allocation. If this is the case, we can change all users to use
@ -274,7 +254,9 @@ Instruction *InstCombiner::visitAllocaInst(AllocaInst &AI) {
// is only subsequently read.
SmallVector<Instruction *, 4> ToDelete;
if (MemTransferInst *Copy = isOnlyCopiedFromConstantGlobal(&AI, ToDelete)) {
if (AI.getAlignment() <= getPointeeAlignment(Copy->getSource(), *TD)) {
unsigned SourceAlign = getOrEnforceKnownAlignment(Copy->getSource(),
AI.getAlignment(), TD);
if (AI.getAlignment() <= SourceAlign) {
DEBUG(dbgs() << "Found alloca equal to global: " << AI << '\n');
DEBUG(dbgs() << " memcpy = " << *Copy << '\n');
for (unsigned i = 0, e = ToDelete.size(); i != e; ++i)

10
test/Transforms/InstCombine/memcpy-from-global.ll
View File

@ -134,3 +134,13 @@ define void @test8() {
; CHECK: bar
ret void
}
define void @test9() {
%A = alloca %U, align 4
%a = bitcast %U* %A to i8*
call void @llvm.memcpy.p0i8.p0i8.i64(i8* %a, i8* bitcast (%U* getelementptr ([2 x %U]* @H, i64 0, i32 1) to i8*), i64 20, i32 4, i1 false)
call void @bar(i8* %a) readonly
; CHECK: @test9
; CHECK-NEXT: call void @bar(i8* bitcast (%U* getelementptr inbounds ([2 x %U]* @H, i64 0, i64 1) to i8*))
ret void
}