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PR17473:

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Don't normalize an expression during postinc transformation unless it's
invertible.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@203719 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Michael Zolotukhin
2014-03-12 21:31:05 +00:00
parent a65ca9dcf0
commit 4a0593ccd3
2 changed files with 88 additions and 3 deletions
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24
lib/Analysis/IVUsers.cpp
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@ -12,7 +12,6 @@
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "iv-users"
#include "llvm/Analysis/IVUsers.h"
#include "llvm/ADT/STLExtras.h"
@ -186,15 +185,34 @@ bool IVUsers::AddUsersImpl(Instruction *I,
if (AddUserToIVUsers) {
// Okay, we found a user that we cannot reduce.
IVUses.push_back(new IVStrideUse(this, User, I));
IVStrideUse &NewUse = IVUses.back();
IVStrideUse &NewUse = AddUser(User, I);
// Autodetect the post-inc loop set, populating NewUse.PostIncLoops.
// The regular return value here is discarded; instead of recording
// it, we just recompute it when we need it.
const SCEV *OriginalISE = ISE;
ISE = TransformForPostIncUse(NormalizeAutodetect,
ISE, User, I,
NewUse.PostIncLoops,
*SE, *DT);
// PostIncNormalization effectively simplifies the expression under
// pre-increment assumptions. Those assumptions (no wrapping) might not
// hold for the post-inc value. Catch such cases by making sure the
// transformation is invertible.
if (OriginalISE != ISE) {
const SCEV *DenormalizedISE =
TransformForPostIncUse(Denormalize, ISE, User, I,
NewUse.PostIncLoops, *SE, *DT);
// If we normalized the expression, but denormalization doesn't give the
// original one, discard this user.
if (OriginalISE != DenormalizedISE) {
DEBUG(dbgs() << " DISCARDING (NORMALIZATION ISN'T INVERTIBLE): "
<< *ISE << '\n');
IVUses.pop_back();
return false;
}
}
DEBUG(if (SE->getSCEV(I) != ISE)
dbgs() << " NORMALIZED TO: " << *ISE << '\n');
}