Changes in directory llvm/lib/Transforms/Scalar:
InstructionCombining.cpp updated: 1.401 -> 1.402 --- Log message: Limit the search depth of MaskedValueIsZero to 6 instructions, to avoid bad cases. This fixes Markus's second testcase in PR639: http://llvm.cs.uiuc.edu/PR639 , and should seal it for good. --- Diffs of the changes: (+14 -10) InstructionCombining.cpp | 24 ++++++++++++++---------- 1 files changed, 14 insertions(+), 10 deletions(-) Index: llvm/lib/Transforms/Scalar/InstructionCombining.cpp diff -u llvm/lib/Transforms/Scalar/InstructionCombining.cpp:1.401 llvm/lib/Transforms/Scalar/InstructionCombining.cpp:1.402 --- llvm/lib/Transforms/Scalar/InstructionCombining.cpp:1.401 Fri Oct 28 23:36:15 2005 +++ llvm/lib/Transforms/Scalar/InstructionCombining.cpp Mon Oct 31 12:35:52 2005 @@ -389,7 +389,8 @@ /// MaskedValueIsZero - Return true if 'V & Mask' is known to be zero. We use /// this predicate to simplify operations downstream. V and Mask are known to /// be the same type. -static bool MaskedValueIsZero(Value *V, ConstantIntegral *Mask) { +static bool MaskedValueIsZero(Value *V, ConstantIntegral *Mask, + unsigned Depth = 0) { // Note, we cannot consider 'undef' to be "IsZero" here. The problem is that // we cannot optimize based on the assumption that it is zero without changing // to to an explicit zero. If we don't change it to zero, other code could @@ -400,6 +401,8 @@ return true; if (ConstantIntegral *CI = dyn_cast<ConstantIntegral>(V)) return ConstantExpr::getAnd(CI, Mask)->isNullValue(); + + if (Depth == 6) return false; // Limit search depth. if (Instruction *I = dyn_cast<Instruction>(V)) { switch (I->getOpcode()) { @@ -408,21 +411,21 @@ if (ConstantIntegral *CI = dyn_cast<ConstantIntegral>(I->getOperand(1))) { ConstantIntegral *C1C2 = cast<ConstantIntegral>(ConstantExpr::getAnd(CI, Mask)); - if (MaskedValueIsZero(I->getOperand(0), C1C2)) + if (MaskedValueIsZero(I->getOperand(0), C1C2, Depth+1)) return true; } // If either the LHS or the RHS are MaskedValueIsZero, the result is zero. - return MaskedValueIsZero(I->getOperand(1), Mask) || - MaskedValueIsZero(I->getOperand(0), Mask); + return MaskedValueIsZero(I->getOperand(1), Mask, Depth+1) || + MaskedValueIsZero(I->getOperand(0), Mask, Depth+1); case Instruction::Or: case Instruction::Xor: // If the LHS and the RHS are MaskedValueIsZero, the result is also zero. - return MaskedValueIsZero(I->getOperand(1), Mask) && - MaskedValueIsZero(I->getOperand(0), Mask); + return MaskedValueIsZero(I->getOperand(1), Mask, Depth+1) && + MaskedValueIsZero(I->getOperand(0), Mask, Depth+1); case Instruction::Select: // If the T and F values are MaskedValueIsZero, the result is also zero. - return MaskedValueIsZero(I->getOperand(2), Mask) && - MaskedValueIsZero(I->getOperand(1), Mask); + return MaskedValueIsZero(I->getOperand(2), Mask, Depth+1) && + MaskedValueIsZero(I->getOperand(1), Mask, Depth+1); case Instruction::Cast: { const Type *SrcTy = I->getOperand(0)->getType(); if (SrcTy == Type::BoolTy) @@ -440,7 +443,7 @@ Constant *NewMask = ConstantExpr::getCast(Mask, I->getOperand(0)->getType()); return MaskedValueIsZero(I->getOperand(0), - cast<ConstantIntegral>(NewMask)); + cast<ConstantIntegral>(NewMask), Depth+1); } } break; @@ -449,7 +452,8 @@ // (shl X, C1) & C2 == 0 iff (X & C2 >>u C1) == 0 if (ConstantUInt *SA = dyn_cast<ConstantUInt>(I->getOperand(1))) return MaskedValueIsZero(I->getOperand(0), - cast<ConstantIntegral>(ConstantExpr::getUShr(Mask, SA))); + cast<ConstantIntegral>(ConstantExpr::getUShr(Mask, SA)), + Depth+1); break; case Instruction::Shr: // (ushr X, C1) & C2 == 0 iff (-1 >> C1) & C2 == 0 _______________________________________________ llvm-commits mailing list llvm-commits@cs.uiuc.edu http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
