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Teach the load analysis driving core instcombine logic and other bits of

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logic to look through pointer casts, making them trivially stronger in
the face of loads and stores with intervening pointer casts.

I've included a few test cases that demonstrate the kind of folding
instcombine can do without pointer casts and then variations which
obfuscate the logic through bitcasts. Without this patch, the variations
all fail to optimize fully.

This is more important now than it has been in the past as I've started
moving the load canonicialization to more closely follow the value type
requirements rather than the pointer type requirements and thus this
needs to be prepared for more pointer casts. When I made the same change
to stores several test cases regressed without logic along these lines
so I wanted to systematically improve matters first.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@220178 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chandler Carruth
2014-10-20 00:24:14 +00:00
parent fc1c1ec435
commit 35c4e071be
4 changed files with 164 additions and 23 deletions
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11
lib/Transforms/Scalar/JumpThreading.cpp
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@@ -901,6 +901,9 @@ bool JumpThreading::SimplifyPartiallyRedundantLoad(LoadInst *LI) {
// If the returned value is the load itself, replace with an undef. This can
// only happen in dead loops.
if (AvailableVal == LI) AvailableVal = UndefValue::get(LI->getType());
if (AvailableVal->getType() != LI->getType())
AvailableVal = CastInst::Create(CastInst::BitCast, AvailableVal,
LI->getType(), "", LI);
LI->replaceAllUsesWith(AvailableVal);
LI->eraseFromParent();
return true;
@@ -1031,7 +1034,13 @@ bool JumpThreading::SimplifyPartiallyRedundantLoad(LoadInst *LI) {
assert(I != AvailablePreds.end() && I->first == P &&
"Didn't find entry for predecessor!");
PN->addIncoming(I->second, I->first);
// If we have an available predecessor but it requires casting, insert the
// cast in the predecessor and use the cast.
Value *PredV = I->second;
if (PredV->getType() != LI->getType())
PredV = CastInst::Create(CastInst::BitCast, PredV, LI->getType(), "", P);
PN->addIncoming(PredV, I->first);
}
//cerr << "PRE: " << *LI << *PN << "\n";