[llvm] r176300 - Fix a bug in instcombine for fmul in fast math mode.

[Quentin Colombet]

Author: qcolombet
Date: Thu Feb 28 15:12:40 2013
New Revision: 176300

URL: http://llvm.org/viewvc/llvm-project?rev=176300&view=rev
Log:
Fix a bug in instcombine for fmul in fast math mode.
The instcombine recognized pattern looks like:
a = b * c
d = a +/- Cst
or
a = b * c
d = Cst +/- a

When creating the new operands for fadd or fsub instruction following the related fmul, the first operand was created with the second original operand (M0 was created with C1) and the second with the first (M1 with Opnd0).

The fix consists in creating the new operands with the appropriate original operand, i.e., M0 with Opnd0 and M1 with C1.


Modified:
    llvm/trunk/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
    llvm/trunk/test/Transforms/InstCombine/fast-math.ll

Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp?rev=176300&r1=176299&r2=176300&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp Thu Feb 28 15:12:40 2013
@@ -402,7 +402,7 @@ Instruction *InstCombiner::visitFMul(Bin
           return ReplaceInstUsesWith(I, V);
       }
 
-      // (MDC +/- C1) * C2 => (MDC * C2) +/- (C1 * C2)
+      // (MDC +/- C1) * C => (MDC * C) +/- (C1 * C)
       Instruction *FAddSub = dyn_cast<Instruction>(Op0);
       if (FAddSub &&
           (FAddSub->getOpcode() == Instruction::FAdd ||
@@ -420,8 +420,8 @@ Instruction *InstCombiner::visitFMul(Bin
 
         if (C1 && C1->getValueAPF().isNormal() &&
             isFMulOrFDivWithConstant(Opnd0)) {
-          Value *M0 = ConstantExpr::getFMul(C1, C);
-          Value *M1 = isNormalFp(cast<ConstantFP>(M0)) ? 
+          Value *M1 = ConstantExpr::getFMul(C1, C);
+          Value *M0 = isNormalFp(cast<ConstantFP>(M1)) ? 
                       foldFMulConst(cast<Instruction>(Opnd0), C, &I) :
                       0;
           if (M0 && M1) {

Modified: llvm/trunk/test/Transforms/InstCombine/fast-math.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/fast-math.ll?rev=176300&r1=176299&r2=176300&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/fast-math.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/fast-math.ll Thu Feb 28 15:12:40 2013
@@ -172,6 +172,17 @@ define double @fmul_distribute3(double %
 ; CHECK: fmul fast double %t2, 0x10000000000000
 }
 
+; ((X*C1) + C2) * C3 => (X * (C1*C3)) + (C2*C3) (i.e. distribution)
+define float @fmul_distribute4(float %f1) {
+  %t1 = fmul float %f1, 6.0e+3
+  %t2 = fsub float 2.0e+3, %t1
+  %t3 = fmul fast float %t2, 5.0e+3
+  ret float %t3
+; CHECK: @fmul_distribute4
+; CHECK: %1 = fmul fast float %f1, 3.000000e+07
+; CHECK: %t3 = fsub fast float 1.000000e+07, %1
+}
+
 ; C1/X * C2 => (C1*C2) / X
 define float @fmul2(float %f1) {
   %t1 = fdiv float 2.0e+3, %f1