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guard fneg with fmf sub flags 

Summary: This change uses fmf subflags to guard optimizations as well as unsafe. These changes originated from D46483.

Reviewers: spatel, hfinkel

Reviewed By: spatel

Subscribers: nemanjai

Differential Revision: https://reviews.llvm.org/D47389

llvm-svn: 334037
This commit is contained in:
Michael Berg 2018-06-05 18:49:47 +00:00
parent b89704fa6f
commit 96925fe0df
2 changed files with 9 additions and 12 deletions
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6
llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
View File

@ -4049,10 +4049,10 @@ SDValue SelectionDAG::getNode(unsigned Opcode, const SDLoc &DL, EVT VT,
break;
case ISD::FNEG:
// -(X-Y) -> (Y-X) is unsafe because when X==Y, -0.0 != +0.0
if (getTarget().Options.UnsafeFPMath && OpOpcode == ISD::FSUB)
// FIXME: FNEG has no fast-math-flags to propagate; use the FSUB's flags?
if ((getTarget().Options.UnsafeFPMath || Flags.hasNoSignedZeros()) &&
OpOpcode == ISD::FSUB)
return getNode(ISD::FSUB, DL, VT, Operand.getOperand(1),
Operand.getOperand(0), Operand.getNode()->getFlags());
Operand.getOperand(0), Flags);
if (OpOpcode == ISD::FNEG) // --X -> X
return Operand.getOperand(0);
break;

15
llvm/test/CodeGen/PowerPC/fmf-propagation.ll
View File

@ -460,28 +460,25 @@ define double @log2_approx(double %x) nounwind {
; -(X - Y) --> (Y - X)
; FMFDEBUG-LABEL: Optimized lowered selection DAG: %bb.0 'fneg_fsub_nozeros_1:'
; FMFDEBUG: fsub {{t[0-9]+}}, {{t[0-9]+}}
; FMFDEBUG: fsub nsz {{t[0-9]+}}, {{t[0-9]+}}
; FMFDEBUG: Type-legalized selection DAG: %bb.0 'fneg_fsub_nozeros_1:'
; GLOBALDEBUG-LABEL: Optimized lowered selection DAG: %bb.0 'fneg_fsub_nozeros_1:'
; GLOBALDEBUG: fsub {{t[0-9]+}}, {{t[0-9]+}}
; GLOBALDEBUG: fsub nsz {{t[0-9]+}}, {{t[0-9]+}}
; GLOBALDEBUG: Type-legalized selection DAG: %bb.0 'fneg_fsub_nozeros_1:'
define float @fneg_fsub_nozeros_1(float %x, float %y, float %z) {
; FMF-LABEL: fneg_fsub_nozeros_1:
; FMF: # %bb.0:
; FMF-NEXT: xssubsp 0, 1, 2
; FMF-NEXT: xxlxor 13, 13, 13
; FMF-NEXT: xssubsp 1, 13, 0
; FMF-NEXT: xssubsp 1, 2, 1
; FMF-NEXT: blr
;
; GLOBAL-LABEL: fneg_fsub_nozeros_1:
; GLOBAL: # %bb.0:
; GLOBAL-NEXT: xssubsp 0, 1, 2
; GLOBAL-NEXT: xxlxor 13, 13, 13
; GLOBAL-NEXT: xssubsp 1, 13, 0
; GLOBAL-NEXT: xssubsp 1, 2, 1
; GLOBAL-NEXT: blr
%neg = fsub float %x, %y
%add = fsub float 0.0, %neg
%add = fsub nsz float 0.0, %neg
ret float %add
}