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fix a bug in my licm rewrite when a load from the promoted memory

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location is being re-stored to the memory location.  We would get
a dangling pointer from the SSAUpdate data structure and miss a 
use.  This fixes PR8068


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@113042 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2010-09-04 00:12:30 +00:00
parent 43c05744b5
commit 469996400c
2 changed files with 56 additions and 3 deletions
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32
lib/Transforms/Scalar/LICM.cpp
View File

@ -743,6 +743,7 @@ void LICM::PromoteAliasSet(AliasSet &AS) {
// Okay, now we can iterate over all the blocks in the loop with uses,
// processing them. Keep track of which loads are loading a live-in value.
SmallVector<LoadInst*, 32> LiveInLoads;
DenseMap<Value*, Value*> ReplacedLoads;
for (unsigned LoopUse = 0, e = LoopUses.size(); LoopUse != e; ++LoopUse) {
Instruction *User = LoopUses[LoopUse];
@ -792,15 +793,17 @@ void LICM::PromoteAliasSet(AliasSet &AS) {
Value *StoredValue = 0;
for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E; ++II) {
if (LoadInst *L = dyn_cast<LoadInst>(II)) {
// If this is a load to an unrelated pointer, ignore it.
// If this is a load from an unrelated pointer, ignore it.
if (!PointerMustAliases.count(L->getOperand(0))) continue;
// If we haven't seen a store yet, this is a live in use, otherwise
// use the stored value.
if (StoredValue)
if (StoredValue) {
L->replaceAllUsesWith(StoredValue);
else
ReplacedLoads[L] = StoredValue;
} else {
LiveInLoads.push_back(L);
}
continue;
}
@ -846,12 +849,35 @@ void LICM::PromoteAliasSet(AliasSet &AS) {
Value *NewVal = SSA.GetValueInMiddleOfBlock(ALoad->getParent());
ALoad->replaceAllUsesWith(NewVal);
CurAST->copyValue(ALoad, NewVal);
ReplacedLoads[ALoad] = NewVal;
}
// Now that everything is rewritten, delete the old instructions from the body
// of the loop. They should all be dead now.
for (unsigned i = 0, e = LoopUses.size(); i != e; ++i) {
Instruction *User = LoopUses[i];
// If this is a load that still has uses, then the load must have been added
// as a live value in the SSAUpdate data structure for a block (e.g. because
// the loaded value was stored later). In this case, we need to recursively
// propagate the updates until we get to the real value.
if (!User->use_empty()) {
Value *NewVal = ReplacedLoads[User];
assert(NewVal && "not a replaced load?");
// Propagate down to the ultimate replacee. The intermediately loads
// could theoretically already have been deleted, so we don't want to
// dereference the Value*'s.
DenseMap<Value*, Value*>::iterator RLI = ReplacedLoads.find(NewVal);
while (RLI != ReplacedLoads.end()) {
NewVal = RLI->second;
RLI = ReplacedLoads.find(NewVal);
}
User->replaceAllUsesWith(NewVal);
CurAST->copyValue(User, NewVal);
}
CurAST->deleteValue(User);
User->eraseFromParent();
}

27
test/Transforms/LICM/crash.ll Normal file
View File

@ -0,0 +1,27 @@
; RUN: opt -licm %s -disable-output
target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64"
target triple = "x86_64-apple-darwin10.0.0"
; PR8068
@g_12 = external global i8, align 1
define void @test1() nounwind ssp {
entry:
br label %for.body
for.body: ; preds = %for.cond, %bb.nph
store i8 0, i8* @g_12, align 1
%tmp6 = load i8* @g_12, align 1
br label %for.cond
for.cond: ; preds = %for.body
store i8 %tmp6, i8* @g_12, align 1
br i1 false, label %for.cond.for.end10_crit_edge, label %for.body
for.cond.for.end10_crit_edge: ; preds = %for.cond
br label %for.end10
for.end10: ; preds = %for.cond.for.end10_crit_edge, %entry
ret void
}