InstCombine: fabs(x) * fabs(x) -> x * x

llvm-svn: 259295

2 files changed, 44 insertions, 4 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
index 160792b0a00..161d3ebca23 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -612,12 +612,23 @@ Instruction *InstCombiner::visitFMul(BinaryOperator &I) {
     }
   }
 
-  // sqrt(X) * sqrt(X) -> X
-  if (AllowReassociate && (Op0 == Op1))
-    if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(Op0))
-      if (II->getIntrinsicID() == Intrinsic::sqrt)
+  if (Op0 == Op1) {
+    if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(Op0)) {
+      // sqrt(X) * sqrt(X) -> X
+      if (AllowReassociate && II->getIntrinsicID() == Intrinsic::sqrt)
         return ReplaceInstUsesWith(I, II->getOperand(0));
 
+      // fabs(X) * fabs(X) -> X * X
+      if (II->getIntrinsicID() == Intrinsic::fabs) {
+        Instruction *FMulVal = BinaryOperator::CreateFMul(II->getOperand(0),
+                                                          II->getOperand(0),
+                                                          I.getName());
+        FMulVal->copyFastMathFlags(&I);
+        return FMulVal;
+      }
+    }
+  }
+
   // Under unsafe algebra do:
   // X * log2(0.5*Y) = X*log2(Y) - X
   if (AllowReassociate) {
diff --git a/llvm/test/Transforms/InstCombine/fmul.ll b/llvm/test/Transforms/InstCombine/fmul.ll
index ac3000fc051..25353e2ef26 100644
--- a/llvm/test/Transforms/InstCombine/fmul.ll
+++ b/llvm/test/Transforms/InstCombine/fmul.ll
@@ -152,3 +152,32 @@ define double @sqrt_squared2(double %f) {
 ; CHECK-NEXT: %mul2 = fmul double %sqrt, %f
 ; CHECK-NEXT: ret double %mul2
 }
+
+declare float @llvm.fabs.f32(float) nounwind readnone
+
+; CHECK-LABEL @fabs_squared(
+; CHECK: %mul = fmul float %x, %x
+define float @fabs_squared(float %x) {
+  %x.fabs = call float @llvm.fabs.f32(float %x)
+  %mul = fmul float %x.fabs, %x.fabs
+  ret float %mul
+}
+
+; CHECK-LABEL @fabs_squared_fast(
+; CHECK: %mul = fmul fast float %x, %x
+define float @fabs_squared_fast(float %x) {
+  %x.fabs = call float @llvm.fabs.f32(float %x)
+  %mul = fmul fast float %x.fabs, %x.fabs
+  ret float %mul
+}
+
+; CHECK-LABEL @fabs_x_fabs(
+; CHECK: call float @llvm.fabs.f32(float %x)
+; CHECK: call float @llvm.fabs.f32(float %y)
+; CHECK: %mul = fmul float %x.fabs, %y.fabs
+define float @fabs_x_fabs(float %x, float %y) {
+  %x.fabs = call float @llvm.fabs.f32(float %x)
+  %y.fabs = call float @llvm.fabs.f32(float %y)
+  %mul = fmul float %x.fabs, %y.fabs
+  ret float %mul
+}