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Don't split critical edges during the AddUsersIfInteresting phase

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of LSR. This makes the AddUsersIfInteresting phase of LSR a pure
analysis instead of a phase that potentially does CFG modifications.

The conditions where this code would actually perform a split are
rare, and in the cases where it actually would do a split the split
is usually undone by CodeGenPrepare, and in cases where splits
actually survive into codegen, they appear to hurt more often than
they help.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@70625 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dan Gohman 2009-05-02 05:36:01 +00:00
parent dd47f88cfe
commit 1dcad96dc6
1 changed files with 1 additions and 14 deletions
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15
lib/Transforms/Scalar/LoopStrengthReduce.cpp
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@ -406,20 +406,7 @@ static bool IVUseShouldUsePostIncValue(Instruction *User, Instruction *IV,
}
// Okay, all uses of IV by PN are in predecessor blocks that really are
// dominated by the latch block. Split the critical edges and use the
// post-incremented value.
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
if (PN->getIncomingValue(i) == IV) {
SplitCriticalEdge(PN->getIncomingBlock(i), PN->getParent(), P, false);
// Splitting the critical edge can reduce the number of entries in this
// PHI.
e = PN->getNumIncomingValues();
if (--NumUses == 0) break;
}
// PHI node might have become a constant value after SplitCriticalEdge.
DeadInsts.push_back(User);
// dominated by the latch block. Use the post-incremented value.
return true;
}