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[MemCpyOpt] Don't perform callslot optimization across may-throw calls

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An exception could prevent a store from occurring but MemCpyOpt's
callslot optimization would fire anyway, causing the store to occur.

This fixes PR27849.

llvm-svn: 270892
This commit is contained in:
David Majnemer 2016-05-26 19:24:24 +00:00
parent 6f9336d4d1
commit d785861d7b
3 changed files with 48 additions and 2 deletions
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14
lib/Transforms/Scalar/MemCpyOptimizer.cpp
View File

@ -496,7 +496,7 @@ static unsigned findCommonAlignment(const DataLayout &DL, const StoreInst *SI,
// This method try to lift a store instruction before position P.
// It will lift the store and its argument + that anything that
// lay alias with these.
// may alias with these.
// The method returns true if it was successful.
static bool moveUp(AliasAnalysis &AA, StoreInst *SI, Instruction *P) {
// If the store alias this position, early bail out.
@ -675,6 +675,8 @@ bool MemCpyOpt::processStore(StoreInst *SI, BasicBlock::iterator &BBI) {
if (C) {
// Check that nothing touches the dest of the "copy" between
// the call and the store.
Value *CpyDest = SI->getPointerOperand()->stripPointerCasts();
bool CpyDestIsLocal = isa<AllocaInst>(CpyDest);
AliasAnalysis &AA = getAnalysis<AAResultsWrapperPass>().getAAResults();
MemoryLocation StoreLoc = MemoryLocation::get(SI);
for (BasicBlock::iterator I = --SI->getIterator(), E = C->getIterator();
@ -683,6 +685,12 @@ bool MemCpyOpt::processStore(StoreInst *SI, BasicBlock::iterator &BBI) {
C = nullptr;
break;
}
// The store to dest may never happen if an exception can be thrown
// between the load and the store.
if (I->mayThrow() && !CpyDestIsLocal) {
C = nullptr;
break;
}
}
}
@ -815,6 +823,10 @@ bool MemCpyOpt::performCallSlotOptzn(Instruction *cpy,
if (destSize < srcSize)
return false;
} else if (Argument *A = dyn_cast<Argument>(cpyDest)) {
// The store to dest may never happen if the call can throw.
if (C->mayThrow())
return false;
if (A->getDereferenceableBytes() < srcSize) {
// If the destination is an sret parameter then only accesses that are
// outside of the returned struct type can trap.

34
test/Transforms/MemCpyOpt/callslot_throw.ll Normal file
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@ -0,0 +1,34 @@
; RUN: opt -S -memcpyopt < %s | FileCheck %s
declare void @may_throw(i32* nocapture %x)
; CHECK-LABEL: define void @test1(
define void @test1(i32* nocapture noalias dereferenceable(4) %x) {
entry:
%t = alloca i32, align 4
call void @may_throw(i32* nonnull %t)
%load = load i32, i32* %t, align 4
store i32 %load, i32* %x, align 4
; CHECK: %[[t:.*]] = alloca i32, align 4
; CHECK-NEXT: call void @may_throw(i32* {{.*}} %[[t]])
; CHECK-NEXT: %[[load:.*]] = load i32, i32* %[[t]], align 4
; CHECK-NEXT: store i32 %[[load]], i32* %x, align 4
ret void
}
declare void @always_throws()
; CHECK-LABEL: define void @test2(
define void @test2(i32* nocapture noalias dereferenceable(4) %x) {
entry:
%t = alloca i32, align 4
call void @may_throw(i32* nonnull %t) nounwind
%load = load i32, i32* %t, align 4
call void @always_throws()
store i32 %load, i32* %x, align 4
; CHECK: %[[t:.*]] = alloca i32, align 4
; CHECK-NEXT: call void @may_throw(i32* {{.*}} %[[t]])
; CHECK-NEXT: %[[load:.*]] = load i32, i32* %[[t]], align 4
; CHECK-NEXT: call void @always_throws()
; CHECK-NEXT: store i32 %[[load]], i32* %x, align 4
ret void
}

2
test/Transforms/MemCpyOpt/loadstore-sret.ll
View File

@ -22,4 +22,4 @@ _ZNSt8auto_ptrIiED1Ev.exit:
ret void
}
declare void @_Z3barv(%"class.std::auto_ptr"* nocapture sret)
declare void @_Z3barv(%"class.std::auto_ptr"* nocapture sret) nounwind