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Reapply r155682, making constant folding more consistent, with a fix to work

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properly with how the code handles all-undef PHI nodes.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@155721 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dan Gohman
2012-04-27 17:50:22 +00:00
parent 04a09a461b
commit 03e091f0b5
5 changed files with 90 additions and 38 deletions
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27
lib/Analysis/ConstantFolding.cpp
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@ -780,14 +780,21 @@ Constant *llvm::ConstantFoldInstruction(Instruction *I,
// all operands are constants.
if (isa<UndefValue>(Incoming))
continue;
// If the incoming value is not a constant, or is a different constant to
// the one we saw previously, then give up.
// If the incoming value is not a constant, then give up.
Constant *C = dyn_cast<Constant>(Incoming);
if (!C || (CommonValue && C != CommonValue))
if (!C)
return 0;
// Fold the PHI's operands.
if (ConstantExpr *NewC = dyn_cast<ConstantExpr>(C))
C = ConstantFoldConstantExpression(NewC, TD, TLI);
// If the incoming value is a different constant to
// the one we saw previously, then give up.
if (CommonValue && C != CommonValue)
return 0;
CommonValue = C;
}
// If we reach here, all incoming values are the same constant or undef.
return CommonValue ? CommonValue : UndefValue::get(PN->getType());
}
@ -795,12 +802,18 @@ Constant *llvm::ConstantFoldInstruction(Instruction *I,
// Scan the operand list, checking to see if they are all constants, if so,
// hand off to ConstantFoldInstOperands.
SmallVector<Constant*, 8> Ops;
for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i)
if (Constant *Op = dyn_cast<Constant>(*i))
Ops.push_back(Op);
else
for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i) {
Constant *Op = dyn_cast<Constant>(*i);
if (!Op)
return 0; // All operands not constant!
// Fold the Instruction's operands.
if (ConstantExpr *NewCE = dyn_cast<ConstantExpr>(Op))
Op = ConstantFoldConstantExpression(NewCE, TD, TLI);
Ops.push_back(Op);
}
if (const CmpInst *CI = dyn_cast<CmpInst>(I))
return ConstantFoldCompareInstOperands(CI->getPredicate(), Ops[0], Ops[1],
TD, TLI);