diff options
Diffstat (limited to 'lib')
| -rw-r--r-- | lib/Target/README.txt | 10 | ||||
| -rw-r--r-- | lib/Transforms/Scalar/InstructionCombining.cpp | 8 |
2 files changed, 8 insertions, 10 deletions
diff --git a/lib/Target/README.txt b/lib/Target/README.txt index 559835e8b5..97546c4db5 100644 --- a/lib/Target/README.txt +++ b/lib/Target/README.txt @@ -1111,16 +1111,6 @@ optimized with "clang -emit-llvm-bc | opt -std-compile-opts". //===---------------------------------------------------------------------===// -We would like to do the following transform in the instcombiner: - - -X/C -> X/-C - -However, this isn't valid if (-X) overflows. We can implement this when we -have the concept of a "C signed subtraction" operator that which is undefined -on overflow. - -//===---------------------------------------------------------------------===// - This was noticed in the entryblock for grokdeclarator in 403.gcc: %tmp = icmp eq i32 %decl_context, 4 diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp index 669ef2d516..b875420e5b 100644 --- a/lib/Transforms/Scalar/InstructionCombining.cpp +++ b/lib/Transforms/Scalar/InstructionCombining.cpp @@ -3077,6 +3077,14 @@ Instruction *InstCombiner::visitSDiv(BinaryOperator &I) { RHS->getValue().exactLogBase2()); return BinaryOperator::CreateAShr(Op0, ShAmt, I.getName()); } + + // -X/C --> X/-C provided the negation doesn't overflow. + if (SubOperator *Sub = dyn_cast<SubOperator>(Op0)) + if (isa<Constant>(Sub->getOperand(0)) && + cast<Constant>(Sub->getOperand(0))->isNullValue() && + Sub->hasNoSignedOverflow()) + return BinaryOperator::CreateSDiv(Sub->getOperand(1), + ConstantExpr::getNeg(RHS)); } // If the sign bits of both operands are zero (i.e. we can prove they are |