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Teach instsimplify to gracefully degrade in the presence of instructions

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not attched to a basic block or function. There are conservatively
correct answers in these cases, and this makes the analysis more useful
in contexts where we have a partially formed bit of IR.

I don't have any way to test this directly... suggestions welcome here,
but I'm not seeing anything sadly. I only found this using a subsequent
patch to the inliner which runs instsimplify on partially inlined
instructions, and even then only on a quite large program. I never got
a reasonable testcase out of it, and anything I do get is likely to be
quite fragile due to requiring an interaction of two different passes,
and the only result being a segfault if it goes wrong.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@153176 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chandler Carruth 2012-03-21 10:58:47 +00:00
parent a8d873e178
commit ff739c1575
1 changed files with 6 additions and 0 deletions
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6
lib/Analysis/InstructionSimplify.cpp
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@ -95,6 +95,12 @@ static bool ValueDominatesPHI(Value *V, PHINode *P, const DominatorTree *DT) {
// Arguments and constants dominate all instructions.
return true;
// If we are processing instructions (and/or basic blocks) that have not been
// fully added to a function, the parent nodes may still be null. Simply
// return the conservative answer in these cases.
if (!I->getParent() || !P->getParent() || !I->getParent()->getParent())
return false;
// If we have a DominatorTree then do a precise test.
if (DT) {
if (!DT->isReachableFromEntry(P->getParent()))