[PATCH] D41322: [InstCombine] Missed optimization in math expression: squashing sqrt functions

[Dmitry Venikov via Phabricator via llvm-commits]

Quolyk created this revision.
Quolyk added reviewers: hfinkel, spatel.

Motivation: https://bugs.llvm.org/show_bug.cgi?id=35592. Related: https://reviews.llvm.org/D41283, https://reviews.llvm.org/D41286


https://reviews.llvm.org/D41322

Files:
  lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
  test/Transforms/InstCombine/fmul.ll


Index: test/Transforms/InstCombine/fmul.ll
===================================================================
--- test/Transforms/InstCombine/fmul.ll
+++ test/Transforms/InstCombine/fmul.ll
@@ -181,3 +181,29 @@
   %mul = fmul float %x.fabs, %y.fabs
   ret float %mul
 }
+
+; CHECK-LABEL @sqrt_a_sqrt_b(
+; CHECK: fmul fast double %a, %b
+; CHECK: call fast double @llvm.sqrt.f64(double %1)
+define double @sqrt_a_sqrt_b(double %a, double %b) {
+  %1 = call fast double @llvm.sqrt.f64(double %a)
+  %2 = call fast double @llvm.sqrt.f64(double %b)
+  %mul = fmul fast double %1, %2
+  ret double %mul
+}
+
+; CHECK-LABEL @sqrt_a_sqrt_b_sqrt_c_sqrt_d(
+; CHECK: fmul fast double %a, %b
+; CHECK: fmul fast double %1, %c
+; CHECK: fmul fast double %2, %d
+; CHECK: call fast double @llvm.sqrt.f64(double %3)
+define double @sqrt_a_sqrt_b_sqrt_c_sqrt_d(double %a, double %b, double %c, double %d) {
+  %1 = call fast double @llvm.sqrt.f64(double %a)
+  %2 = call fast double @llvm.sqrt.f64(double %b)
+  %mul = fmul fast double %1, %2
+  %3 = call fast double @llvm.sqrt.f64(double %c)
+  %mul1 = fmul fast double %mul, %3
+  %4 = call fast double @llvm.sqrt.f64(double %d)
+  %mul2 = fmul fast double %mul1, %4
+  ret double %mul2
+}
Index: lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
===================================================================
--- lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -728,6 +728,23 @@
     }
   }
 
+  // sqrt(a) * sqrt(b) -> sqrt(a * b)
+  if (AllowReassociate) {
+    IntrinsicInst *I0 = dyn_cast<IntrinsicInst>(Op0);
+    IntrinsicInst *I1 = dyn_cast<IntrinsicInst>(Op1);
+    if (I0 && I1 &&
+        I0->getIntrinsicID() == Intrinsic::sqrt &&
+        I1->getIntrinsicID() == Intrinsic::sqrt) {
+      Value *Opnd0 = I0->getOperand(0);
+      Value *Opnd1 = I1->getOperand(0);
+      Builder.setFastMathFlags(I.getFastMathFlags());
+      Value *FMulVal = Builder.CreateFMul(Opnd0, Opnd1);
+      Value *Sqrt = Intrinsic::getDeclaration(I.getModule(), Intrinsic::sqrt, I.getType());
+      Value *SqrtCall = Builder.CreateCall(Sqrt, FMulVal);
+      return replaceInstUsesWith(I, SqrtCall);
+    }
+  }
+
   // Handle symmetric situation in a 2-iteration loop
   Value *Opnd0 = Op0;
   Value *Opnd1 = Op1;


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