diff options
author | Nick Lewycky <nicholas@mxc.ca> | 2014-05-14 03:03:05 +0000 |
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committer | Nick Lewycky <nicholas@mxc.ca> | 2014-05-14 03:03:05 +0000 |
commit | 8f844490938e53e21040413d48d9eea926a06dcc (patch) | |
tree | 489d142f910fd78ac4ab94a2ff92df45534a213e /lib | |
parent | ee8af3e2a03495f3d846900fab56be324a0af167 (diff) |
Optimize integral reciprocal (udiv 1, x and sdiv 1, x) to not use division. This fires exactly once in a clang bootstrap, but covers a few different results from http://www.cs.utah.edu/~regehr/souper/
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208750 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'lib')
-rw-r--r-- | lib/Transforms/InstCombine/InstCombineMulDivRem.cpp | 21 |
1 files changed, 20 insertions, 1 deletions
diff --git a/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp index 78689933f49..9996ebc2e74 100644 --- a/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp +++ b/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp @@ -727,7 +727,7 @@ Instruction *InstCombiner::commonIDivTransforms(BinaryOperator &I) { if (Instruction::BinaryOps(LHS->getOpcode()) == I.getOpcode()) if (ConstantInt *LHSRHS = dyn_cast<ConstantInt>(LHS->getOperand(1))) { if (MultiplyOverflows(RHS, LHSRHS, - I.getOpcode()==Instruction::SDiv)) + I.getOpcode() == Instruction::SDiv)) return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType())); return BinaryOperator::Create(I.getOpcode(), LHS->getOperand(0), ConstantExpr::getMul(RHS, LHSRHS)); @@ -743,6 +743,25 @@ Instruction *InstCombiner::commonIDivTransforms(BinaryOperator &I) { } } + if (ConstantInt *One = dyn_cast<ConstantInt>(Op0)) { + if (One->isOne() && !I.getType()->isIntegerTy(1)) { + bool isSigned = I.getOpcode() == Instruction::SDiv; + if (isSigned) { + // If Op1 is 0 then it's undefined behaviour, if Op1 is 1 then the + // result is one, if Op1 is -1 then the result is minus one, otherwise + // it's zero. + Value *Inc = Builder->CreateAdd(Op1, One); + Value *Cmp = Builder->CreateICmpULT( + Inc, ConstantInt::get(I.getType(), 3)); + return SelectInst::Create(Cmp, Op1, ConstantInt::get(I.getType(), 0)); + } else { + // If Op1 is 0 then it's undefined behaviour. If Op1 is 1 then the + // result is one, otherwise it's zero. + return new ZExtInst(Builder->CreateICmpEQ(Op1, One), I.getType()); + } + } + } + // See if we can fold away this div instruction. if (SimplifyDemandedInstructionBits(I)) return &I; |