[PATCH] D32596: [InstCombine] Transform fmul X, +2.0 --> fadd X, X.

[Chad Rosier via Phabricator via llvm-commits]

mcrosier updated this revision to Diff 96982.
mcrosier added a comment.

-Add test case to check fadd X, X is canonical form, per Eli's request.


https://reviews.llvm.org/D32596

Files:
  lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
  test/Transforms/InstCombine/fast-math.ll
  test/Transforms/InstCombine/fmul.ll
  test/Transforms/InstCombine/fold-fops-into-selects.ll


Index: test/Transforms/InstCombine/fold-fops-into-selects.ll
===================================================================
--- test/Transforms/InstCombine/fold-fops-into-selects.ll
+++ test/Transforms/InstCombine/fold-fops-into-selects.ll
@@ -32,11 +32,11 @@
 define float @test4(i1 %A, float %B) {
 EntryBlock:
   %cf = select i1 %A, float 1.000000e+00, float %B
-  %op = fmul float 2.000000e+00, %cf
+  %op = fmul float 3.000000e+00, %cf
   ret float %op
 ; CHECK-LABEL: @test4(
-; CHECK: [[OP:%.*]] = fmul float %B, 2.000000e+00
-; CHECK: select i1 %A, float 2.000000e+00, float [[OP]]
+; CHECK: [[OP:%.*]] = fmul float %B, 3.000000e+00
+; CHECK: select i1 %A, float 3.000000e+00, float [[OP]]
 }
 
 define float @test5(i1 %A, float %B) {
Index: test/Transforms/InstCombine/fmul.ll
===================================================================
--- test/Transforms/InstCombine/fmul.ll
+++ test/Transforms/InstCombine/fmul.ll
@@ -124,6 +124,36 @@
 ; CHECK: fadd fast float
 }
 
+; X * 2.0 => X + X
+define float @test12(float %x) {
+  %mul = fmul float %x, 2.0
+  ret float %mul
+
+; CHECK-LABEL: @test12(
+; CHECK: fadd float %x, %x
+; CHECK: ret
+}
+
+; X * 2.0 => X + X (w/fast flag)
+define float @test13(float %x) {
+  %mul = fmul fast float %x, 2.0
+  ret float %mul
+
+; CHECK-LABEL: @test13(
+; CHECK: fadd fast float %x, %x
+; CHECK: ret
+}
+
+; Check to make sure fadd X, X is the canonical form.
+define float @test14(float %x) {
+  %add = fadd float %x, %x
+  ret float %add
+
+; CHECK-LABEL: @test14(
+; CHECK: fadd float %x, %x
+; CHECK: ret
+}
+
 ; PR21126: http://llvm.org/bugs/show_bug.cgi?id=21126
 ; With unsafe/fast math, sqrt(X) * sqrt(X) is just X.
 declare double @llvm.sqrt.f64(double)
Index: test/Transforms/InstCombine/fast-math.ll
===================================================================
--- test/Transforms/InstCombine/fast-math.ll
+++ test/Transforms/InstCombine/fast-math.ll
@@ -243,7 +243,7 @@
 define float @fmul2_disable(float %f1) {
   %div = fdiv fast float 1.000000e+00, %f1
   store float %div, float* @fmul2_external
-  %mul = fmul fast float %div, 2.000000e+00
+  %mul = fmul fast float %div, 3.000000e+00
   ret float %mul
 ; CHECK-LABEL: @fmul2_disable
 ; CHECK: store
Index: lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
===================================================================
--- lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -625,6 +625,13 @@
       return RI;
     }
 
+    // (fmul X, 2.0) --> (fadd X, X)
+    if (match(Op1, m_SpecificFP(+2.0))) {
+      Instruction *RI = BinaryOperator::CreateFAdd(Op0, Op0);
+      RI->copyFastMathFlags(&I);
+      return RI;
+    }
+
     Constant *C = cast<Constant>(Op1);
     if (AllowReassociate && isFiniteNonZeroFp(C)) {
       // Let MDC denote an expression in one of these forms:


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