[PATCH] D72319: [InstCombine] Adding Z / (1.0 / Y) => (Y * Z)

[Raghesh Aloor via Phabricator via llvm-commits]

raghesh updated this revision to Diff 237069.
raghesh edited the summary of this revision.
raghesh removed a reviewer: llvm-commits.
raghesh added a comment.

This revision is updated with the expected change in the testcase test/Transforms/InstCombine/fdiv-to-fmul-opt.ll. Other comments are addressed too.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D72319/new/

https://reviews.llvm.org/D72319

Files:
  llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
  llvm/test/Transforms/InstCombine/fdiv.ll


Index: llvm/test/Transforms/InstCombine/fdiv.ll
===================================================================
--- llvm/test/Transforms/InstCombine/fdiv.ll
+++ llvm/test/Transforms/InstCombine/fdiv.ll
@@ -187,12 +187,12 @@
   ret float %div2
 }
 
-; Z / (1.0 / Y)
+; Z / (1.0 / Y) ==> Y * Z
 
 define float @div_with_div_denominator_with_one_as_numerator_extra_use(float %x, float %y, float %z) {
 ; CHECK-LABEL: @div_with_div_denominator_with_one_as_numerator_extra_use(
 ; CHECK-NEXT:    [[DIV1:%.*]] = fdiv float 1.000000e+00, [[Y:%.*]]
-; CHECK-NEXT:    [[DIV2:%.*]] = fdiv reassoc arcp float [[Z:%.*]], [[DIV1]]
+; CHECK-NEXT:    [[DIV2:%.*]] = fmul reassoc arcp float [[Y]], [[Z:%.*]]
 ; CHECK-NEXT:    call void @use_f32(float [[DIV1]])
 ; CHECK-NEXT:    ret float [[DIV2]]
 ;
Index: llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -1239,6 +1239,14 @@
       Value *YZ = Builder.CreateFMulFMF(Y, Op0, &I);
       return BinaryOperator::CreateFDivFMF(YZ, X, &I);
     }
+    // Z / (1.0 / Y) => (Y * Z)
+    //
+    // This is a special case of Z / (X / Y) => (Y * Z) / X, with X = 1.0. The
+    // m_OneUse check is avoided because even in the case of the multiple uses
+    // for 1.0/Y, the number of instructions remain the same and a division is
+    // replaced by a multiplication.
+    if (match(Op1, m_FDiv(m_SpecificFP(1.0), m_Value(Y))))
+      return BinaryOperator::CreateFMulFMF(Y, Op0, &I);
   }
 
   if (I.hasAllowReassoc() && Op0->hasOneUse() && Op1->hasOneUse()) {


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