[PATCH] D81491: [InstCombine] reassociate FP diff of sums into sum of diffs

[Sanjay Patel via Phabricator via llvm-commits]

spatel updated this revision to Diff 269616.
spatel added a comment.

Patch updated:
Corrected the final op - we subtract the 2nd reduction's accumulator variable.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D81491/new/

https://reviews.llvm.org/D81491

Files:
  llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
  llvm/test/Transforms/InstCombine/vector-reductions.ll
  llvm/test/Transforms/PhaseOrdering/X86/vector-reductions.ll


Index: llvm/test/Transforms/PhaseOrdering/X86/vector-reductions.ll
===================================================================
--- llvm/test/Transforms/PhaseOrdering/X86/vector-reductions.ll
+++ llvm/test/Transforms/PhaseOrdering/X86/vector-reductions.ll
@@ -240,10 +240,9 @@
 ; CHECK-NEXT:    [[TMP1:%.*]] = load <4 x float>, <4 x float>* [[TMP0]], align 4
 ; CHECK-NEXT:    [[TMP2:%.*]] = bitcast float* [[VEC1:%.*]] to <4 x float>*
 ; CHECK-NEXT:    [[TMP3:%.*]] = load <4 x float>, <4 x float>* [[TMP2]], align 4
-; CHECK-NEXT:    [[TMP4:%.*]] = call fast float @llvm.experimental.vector.reduce.v2.fadd.f32.v4f32(float 0.000000e+00, <4 x float> [[TMP1]])
-; CHECK-NEXT:    [[TMP5:%.*]] = call fast float @llvm.experimental.vector.reduce.v2.fadd.f32.v4f32(float 0.000000e+00, <4 x float> [[TMP3]])
-; CHECK-NEXT:    [[ADD_3:%.*]] = fsub fast float [[TMP4]], [[TMP5]]
-; CHECK-NEXT:    [[CMP3:%.*]] = fcmp fast ole float [[ADD_3]], [[TOLERANCE:%.*]]
+; CHECK-NEXT:    [[TMP4:%.*]] = fsub fast <4 x float> [[TMP1]], [[TMP3]]
+; CHECK-NEXT:    [[TMP5:%.*]] = call fast float @llvm.experimental.vector.reduce.v2.fadd.f32.v4f32(float 0.000000e+00, <4 x float> [[TMP4]])
+; CHECK-NEXT:    [[CMP3:%.*]] = fcmp fast ole float [[TMP5]], [[TOLERANCE:%.*]]
 ; CHECK-NEXT:    [[COND:%.*]] = zext i1 [[CMP3]] to i32
 ; CHECK-NEXT:    ret i32 [[COND]]
 ;
Index: llvm/test/Transforms/InstCombine/vector-reductions.ll
===================================================================
--- llvm/test/Transforms/InstCombine/vector-reductions.ll
+++ llvm/test/Transforms/InstCombine/vector-reductions.ll
@@ -7,9 +7,9 @@
 
 define float @diff_of_sums_v4f32(float %a0, <4 x float> %v0, float %a1, <4 x float> %v1) {
 ; CHECK-LABEL: @diff_of_sums_v4f32(
-; CHECK-NEXT:    [[R0:%.*]] = call float @llvm.experimental.vector.reduce.v2.fadd.f32.v4f32(float [[A0:%.*]], <4 x float> [[V0:%.*]])
-; CHECK-NEXT:    [[R1:%.*]] = call float @llvm.experimental.vector.reduce.v2.fadd.f32.v4f32(float [[A1:%.*]], <4 x float> [[V1:%.*]])
-; CHECK-NEXT:    [[R:%.*]] = fsub reassoc nsz float [[R0]], [[R1]]
+; CHECK-NEXT:    [[TMP1:%.*]] = fsub reassoc nsz <4 x float> [[V0:%.*]], [[V1:%.*]]
+; CHECK-NEXT:    [[TMP2:%.*]] = call reassoc nsz float @llvm.experimental.vector.reduce.v2.fadd.f32.v4f32(float [[A0:%.*]], <4 x float> [[TMP1]])
+; CHECK-NEXT:    [[R:%.*]] = fsub reassoc nsz float [[TMP2]], [[A1:%.*]]
 ; CHECK-NEXT:    ret float [[R]]
 ;
   %r0 = call float @llvm.experimental.vector.reduce.v2.fadd.f32.v4f32(float %a0, <4 x float> %v0)
@@ -18,6 +18,8 @@
   ret float %r
 }
 
+; negative test - fsub must allow reassociation
+
 define float @diff_of_sums_v4f32_fmf(float %a0, <4 x float> %v0, float %a1, <4 x float> %v1) {
 ; CHECK-LABEL: @diff_of_sums_v4f32_fmf(
 ; CHECK-NEXT:    [[R0:%.*]] = call fast float @llvm.experimental.vector.reduce.v2.fadd.f32.v4f32(float [[A0:%.*]], <4 x float> [[V0:%.*]])
@@ -31,6 +33,8 @@
   ret float %r
 }
 
+; negative test - extra uses could create extra instructions
+
 define float @diff_of_sums_extra_use1(float %a0, <4 x float> %v0, float %a1, <4 x float> %v1) {
 ; CHECK-LABEL: @diff_of_sums_extra_use1(
 ; CHECK-NEXT:    [[R0:%.*]] = call fast float @llvm.experimental.vector.reduce.v2.fadd.f32.v4f32(float [[A0:%.*]], <4 x float> [[V0:%.*]])
@@ -46,6 +50,8 @@
   ret float %r
 }
 
+; negative test - extra uses could create extra instructions
+
 define float @diff_of_sums_extra_use2(float %a0, <4 x float> %v0, float %a1, <4 x float> %v1) {
 ; CHECK-LABEL: @diff_of_sums_extra_use2(
 ; CHECK-NEXT:    [[R0:%.*]] = call fast float @llvm.experimental.vector.reduce.v2.fadd.f32.v4f32(float [[A0:%.*]], <4 x float> [[V0:%.*]])
@@ -61,6 +67,8 @@
   ret float %r
 }
 
+; negative test - can't reassociate different vector types
+
 define float @diff_of_sums_type_mismatch(float %a0, <4 x float> %v0, float %a1, <8 x float> %v1) {
 ; CHECK-LABEL: @diff_of_sums_type_mismatch(
 ; CHECK-NEXT:    [[R0:%.*]] = call fast float @llvm.experimental.vector.reduce.v2.fadd.f32.v4f32(float [[A0:%.*]], <4 x float> [[V0:%.*]])
Index: llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -2217,6 +2217,23 @@
       return BinaryOperator::CreateFSubFMF(XZ, YW, &I);
     }
 
+    auto m_FaddRdx = [](Value *&Sum, Value *&Vec) {
+      return m_OneUse(
+          m_Intrinsic<Intrinsic::experimental_vector_reduce_v2_fadd>(
+              m_Value(Sum), m_Value(Vec)));
+    };
+    Value *A0, *A1, *V0, *V1;
+    if (match(Op0, m_FaddRdx(A0, V0)) && match(Op1, m_FaddRdx(A1, V1)) &&
+        V0->getType() == V1->getType()) {
+      // Difference of sums is sum of differences:
+      // add_rdx(A0, V0) - add_rdx(A1, V1) --> add_rdx(A0, V0 - V1) - A1
+      Value *Sub = Builder.CreateFSubFMF(V0, V1, &I);
+      Value *Rdx = Builder.CreateIntrinsic(
+          Intrinsic::experimental_vector_reduce_v2_fadd,
+          {A0->getType(), Sub->getType()}, {A0, Sub}, &I);
+      return BinaryOperator::CreateFSubFMF(Rdx, A1, &I);
+    }
+
     if (Instruction *F = factorizeFAddFSub(I, Builder))
       return F;
 


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