[llvm-commits] [llvm] r128546 - in /llvm/trunk: lib/Transforms/InstCombine/InstCombineMulDivRem.cpp test/Transforms/InstCombine/fdiv.ll

[Benjamin Kramer]

Author: d0k
Date: Wed Mar 30 10:42:35 2011
New Revision: 128546

URL: http://llvm.org/viewvc/llvm-project?rev=128546&view=rev
Log:
InstCombine: If the divisor of an fdiv has an exact inverse, turn it into an fmul.

Fixes PR9587.

Added:
    llvm/trunk/test/Transforms/InstCombine/fdiv.ll
Modified:
    llvm/trunk/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp

Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp?rev=128546&r1=128545&r2=128546&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp Wed Mar 30 10:42:35 2011
@@ -452,6 +452,18 @@
   if (Value *V = SimplifyFDivInst(Op0, Op1, TD))
     return ReplaceInstUsesWith(I, V);
 
+  if (ConstantFP *Op1C = dyn_cast<ConstantFP>(Op1)) {
+    const APFloat &Op1F = Op1C->getValueAPF();
+
+    // If the divisor has an exact multiplicative inverse we can turn the fdiv
+    // into a cheaper fmul.
+    APFloat Reciprocal(Op1F.getSemantics());
+    if (Op1F.getExactInverse(&Reciprocal)) {
+      ConstantFP *RFP = ConstantFP::get(Builder->getContext(), Reciprocal);
+      return BinaryOperator::CreateFMul(Op0, RFP);
+    }
+  }
+
   return 0;
 }
 

Added: llvm/trunk/test/Transforms/InstCombine/fdiv.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/fdiv.ll?rev=128546&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/fdiv.ll (added)
+++ llvm/trunk/test/Transforms/InstCombine/fdiv.ll Wed Mar 30 10:42:35 2011
@@ -0,0 +1,25 @@
+; RUN: opt -S -instcombine < %s | FileCheck %s
+
+define float @test1(float %x) nounwind readnone ssp {
+  %div = fdiv float %x, 0x3810000000000000
+  ret float %div
+
+; CHECK: @test1
+; CHECK-NEXT: fmul float %x, 0x47D0000000000000
+}
+
+define float @test2(float %x) nounwind readnone ssp {
+  %div = fdiv float %x, 0x47E0000000000000
+  ret float %div
+
+; CHECK: @test2
+; CHECK-NEXT: fmul float %x, 0x3800000000000000
+}
+
+define float @test3(float %x) nounwind readnone ssp {
+  %div = fdiv float %x, 0x36A0000000000000
+  ret float %div
+
+; CHECK: @test3
+; CHECK-NEXT: fdiv float %x, 0x36A0000000000000
+}