diff options
| -rw-r--r-- | lib/CodeGen/SelectionDAG/SelectionDAG.cpp | 3 | ||||
| -rw-r--r-- | test/CodeGen/X86/neg_fp.ll | 12 |
2 files changed, 14 insertions, 1 deletions
diff --git a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp index bda9d934a4..f5287b0cf2 100644 --- a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp +++ b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp @@ -2357,7 +2357,8 @@ SDValue SelectionDAG::getNode(unsigned Opcode, DebugLoc DL, return Operand.getOperand(0); break; case ISD::FNEG: - if (OpOpcode == ISD::FSUB) // -(X-Y) -> (Y-X) + // -(X-Y) -> (Y-X) is unsafe because when X==Y, -0.0 != +0.0 + if (UnsafeFPMath && OpOpcode == ISD::FSUB) return getNode(ISD::FSUB, VT, Operand.getNode()->getOperand(1), Operand.getNode()->getOperand(0)); if (OpOpcode == ISD::FNEG) // --X -> X diff --git a/test/CodeGen/X86/neg_fp.ll b/test/CodeGen/X86/neg_fp.ll new file mode 100644 index 0000000000..55c76549ff --- /dev/null +++ b/test/CodeGen/X86/neg_fp.ll @@ -0,0 +1,12 @@ +; RUN: llvm-as < %s | llc -march=x86 -mattr=+sse41 -o %t -f +; RUN: grep xorps %t | count 1 + +; Test that when we don't -enable-unsafe-fp-math, we don't do the optimization +; -0 - (A - B) to (B - A) because A==B, -0 != 0 + +define float @negfp(float %a, float %b) { +entry: + %sub = sub float %a, %b ; <float> [#uses=1] + %neg = sub float -0.000000e+00, %sub ; <float> [#uses=1] + ret float %neg +}
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