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Try to harden the recursive simplification still further. This is again

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spotted by inspection, and I've crafted no test case that triggers it on
my machine, but some of the windows builders are hitting what looks like
memory corruption, so *something* is amiss here.

This patch takes a more generalized approach to eliminating
double-visits. Imagine code such as:

  %x = ...
  %y = add %x, 1
  %z = add %x, %y

You can imagine that if we simplify %x, we would add %y and %z to the
list. If the use-chain order happens to cause us to add them in reverse
order, we could pull %y off first, and simplify it, adding %z to the
list. We now have %z on the list twice, and will reference it after it
is deleted.

Currently, all my test cases happen to not trigger this, likely due to
the use-chain ordering, but there seems no guarantee that such
a situation could not occur, so we should handle it correctly.

Again, if anyone knows how to craft a testcase that actually triggers
this, please let me know.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@153397 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chandler Carruth 2012-03-24 22:34:26 +00:00
parent c5b785b91c
commit 6231d5be41
1 changed files with 8 additions and 7 deletions
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15
lib/Analysis/InstructionSimplify.cpp
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@ -21,6 +21,7 @@
#include "llvm/GlobalAlias.h"
#include "llvm/Operator.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/ConstantFolding.h"
@ -2834,7 +2835,7 @@ static bool replaceAndRecursivelySimplifyImpl(Instruction *I, Value *SimpleV,
const TargetLibraryInfo *TLI,
const DominatorTree *DT) {
bool Simplified = false;
SmallVector<Instruction *, 8> Worklist;
SmallSetVector<Instruction *, 8> Worklist;
// If we have an explicit value to collapse to, do that round of the
// simplification loop by hand initially.
@ -2842,7 +2843,7 @@ static bool replaceAndRecursivelySimplifyImpl(Instruction *I, Value *SimpleV,
for (Value::use_iterator UI = I->use_begin(), UE = I->use_end(); UI != UE;
++UI)
if (*UI != I)
Worklist.push_back(cast<Instruction>(*UI));
Worklist.insert(cast<Instruction>(*UI));
// Replace the instruction with its simplified value.
I->replaceAllUsesWith(SimpleV);
@ -2852,11 +2853,12 @@ static bool replaceAndRecursivelySimplifyImpl(Instruction *I, Value *SimpleV,
if (I->getParent())
I->eraseFromParent();
} else {
Worklist.push_back(I);
Worklist.insert(I);
}
while (!Worklist.empty()) {
I = Worklist.pop_back_val();
// Note that we must test the size on each iteration, the worklist can grow.
for (unsigned Idx = 0; Idx != Worklist.size(); ++Idx) {
I = Worklist[Idx];
// See if this instruction simplifies.
SimpleV = SimplifyInstruction(I, TD, TLI, DT);
@ -2870,8 +2872,7 @@ static bool replaceAndRecursivelySimplifyImpl(Instruction *I, Value *SimpleV,
// uses of To on the recursive step in most cases.
for (Value::use_iterator UI = I->use_begin(), UE = I->use_end(); UI != UE;
++UI)
if (*UI != I)
Worklist.push_back(cast<Instruction>(*UI));
Worklist.insert(cast<Instruction>(*UI));
// Replace the instruction with its simplified value.
I->replaceAllUsesWith(SimpleV);