From: Duncan Sands <baldrick@free.fr>
Date: Sun, 8 Apr 2012 18:08:12 +0000 (+0000)
Subject: Only have codegen turn fdiv by a constant into fmul by the reciprocal
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=3ef3fcfc0414b96d626b706c6151596684b7d134;p=oota-llvm.git

Only have codegen turn fdiv by a constant into fmul by the reciprocal
when -ffast-math, i.e. don't just always do it if the reciprocal can
be formed exactly.  There is already an IR level transform that does
that, and it does it more carefully.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@154296 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index ebffb8562ef..f1b9f4385e4 100644
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -5725,16 +5725,14 @@ SDValue DAGCombiner::visitFDIV(SDNode *N) {
   if (N0CFP && N1CFP && VT != MVT::ppcf128)
     return DAG.getNode(ISD::FDIV, N->getDebugLoc(), VT, N0, N1);
 
-  // fold (fdiv X, c2) -> fmul X, 1/c2 if there is no precision loss or if
-  // losing precision is acceptable.
-  if (N1CFP && VT != MVT::ppcf128) {
+  // fold (fdiv X, c2) -> fmul X, 1/c2 if losing precision is acceptable.
+  if (N1CFP && VT != MVT::ppcf128 && DAG.getTarget().Options.UnsafeFPMath) {
     // Compute the reciprocal 1.0 / c2.
     APFloat N1APF = N1CFP->getValueAPF();
     APFloat Recip(N1APF.getSemantics(), 1); // 1.0
     APFloat::opStatus st = Recip.divide(N1APF, APFloat::rmNearestTiesToEven);
     // Only do the transform if the reciprocal is not too horrible (eg not NaN).
-    if (st == APFloat::opOK || (st == APFloat::opInexact &&
-                                DAG.getTarget().Options.UnsafeFPMath))
+    if (st == APFloat::opOK || st == APFloat::opInexact)
       return DAG.getNode(ISD::FMUL, N->getDebugLoc(), VT, N0,
                          DAG.getConstantFP(Recip, VT));
   }
diff --git a/test/CodeGen/X86/fdiv.ll b/test/CodeGen/X86/fdiv.ll
index 553f14efa13..82b9190b9a5 100644
--- a/test/CodeGen/X86/fdiv.ll
+++ b/test/CodeGen/X86/fdiv.ll
@@ -1,22 +1,17 @@
-; RUN: llc < %s -march=x86-64 | FileCheck %s
-; RUN: llc < %s -march=x86-64 -enable-unsafe-fp-math | FileCheck -check-prefix=UNSAFE %s
+; RUN: llc < %s -march=x86-64 -enable-unsafe-fp-math | FileCheck %s
 
 define double @exact(double %x) {
-; Exact division by a constant always converted to multiplication.
+; Exact division by a constant converted to multiplication.
 ; CHECK: @exact
 ; CHECK: mulsd
-; UNSAFE: @exact
-; UNSAFE: mulsd
   %div = fdiv double %x, 2.0
   ret double %div
 }
 
 define double @inexact(double %x) {
-; Inexact division by a constant converted to multiplication if unsafe-math.
+; Inexact division by a constant converted to multiplication.
 ; CHECK: @inexact
-; CHECK: divsd
-; UNSAFE: @inexact
-; UNSAFE: mulsd
+; CHECK: mulsd
   %div = fdiv double %x, 0x41DFFFFFFFC00000 
   ret double %div
 }
@@ -25,8 +20,6 @@ define double @funky(double %x) {
 ; No conversion to multiplication if too funky.
 ; CHECK: @funky
 ; CHECK: divsd
-; UNSAFE: @funky
-; UNSAFE: divsd
   %div = fdiv double %x, 0.0
   ret double %div
 }