[llvm] [LV] Handle FSub Partial Reductions (PR #191186)

[Florian Hahn via llvm-commits]

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@@ -185,4 +185,117 @@ exit:
   ret i32 %sub
 }
 
+define float @fsub_reduction(float %startval, ptr %src1, ptr %src2) #0 {
+; CHECK-EPI-LABEL: define float @fsub_reduction(
+; CHECK-EPI-SAME: float [[STARTVAL:%.*]], ptr [[SRC1:%.*]], ptr [[SRC2:%.*]]) #[[ATTR0]] {
+; CHECK-EPI-NEXT:  [[VECTOR_MAIN_LOOP_ITER_CHECK:.*:]]
+; CHECK-EPI-NEXT:    br label %[[VECTOR_PH:.*]]
+; CHECK-EPI:       [[VECTOR_PH]]:
+; CHECK-EPI-NEXT:    br label %[[VECTOR_BODY:.*]]
+; CHECK-EPI:       [[VECTOR_BODY]]:
+; CHECK-EPI-NEXT:    [[INDEX:%.*]] = phi i32 [ 0, %[[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], %[[VECTOR_BODY]] ]
+; CHECK-EPI-NEXT:    [[VEC_PHI:%.*]] = phi <2 x float> [ splat (float -0.000000e+00), %[[VECTOR_PH]] ], [ [[PARTIAL_REDUCE:%.*]], %[[VECTOR_BODY]] ]
+; CHECK-EPI-NEXT:    [[TMP0:%.*]] = getelementptr half, ptr [[SRC1]], i32 [[INDEX]]
+; CHECK-EPI-NEXT:    [[WIDE_LOAD:%.*]] = load <4 x half>, ptr [[TMP0]], align 4
+; CHECK-EPI-NEXT:    [[TMP1:%.*]] = getelementptr half, ptr [[SRC2]], i32 [[INDEX]]
+; CHECK-EPI-NEXT:    [[WIDE_LOAD1:%.*]] = load <4 x half>, ptr [[TMP1]], align 4
+; CHECK-EPI-NEXT:    [[TMP2:%.*]] = fpext <4 x half> [[WIDE_LOAD]] to <4 x float>
+; CHECK-EPI-NEXT:    [[TMP3:%.*]] = fpext <4 x half> [[WIDE_LOAD1]] to <4 x float>
+; CHECK-EPI-NEXT:    [[TMP4:%.*]] = fmul reassoc contract <4 x float> [[TMP2]], [[TMP3]]
+; CHECK-EPI-NEXT:    [[PARTIAL_REDUCE]] = call reassoc contract <2 x float> @llvm.vector.partial.reduce.fadd.v2f32.v4f32(<2 x float> [[VEC_PHI]], <4 x float> [[TMP4]])
+; CHECK-EPI-NEXT:    [[INDEX_NEXT]] = add nuw i32 [[INDEX]], 4
+; CHECK-EPI-NEXT:    [[TMP5:%.*]] = icmp eq i32 [[INDEX_NEXT]], 36
+; CHECK-EPI-NEXT:    br i1 [[TMP5]], label %[[MIDDLE_BLOCK:.*]], label %[[VECTOR_BODY]], !llvm.loop [[LOOP6:![0-9]+]]
+; CHECK-EPI:       [[MIDDLE_BLOCK]]:
+; CHECK-EPI-NEXT:    [[TMP6:%.*]] = call reassoc contract float @llvm.vector.reduce.fadd.v2f32(float -0.000000e+00, <2 x float> [[PARTIAL_REDUCE]])
+; CHECK-EPI-NEXT:    [[TMP7:%.*]] = fsub float [[STARTVAL]], [[TMP6]]
+; CHECK-EPI-NEXT:    br label %[[VEC_EPILOG_VECTOR_BODY:.*]]
+; CHECK-EPI:       [[VEC_EPILOG_VECTOR_BODY]]:
+; CHECK-EPI-NEXT:    br label %[[LOOP:.*]]
+; CHECK-EPI:       [[LOOP]]:
+; CHECK-EPI-NEXT:    [[IV:%.*]] = phi i32 [ 36, %[[VEC_EPILOG_VECTOR_BODY]] ], [ [[IV_NEXT:%.*]], %[[LOOP]] ]
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fhahn wrote:

it looks like this is intended to test epilogue vectorization, but there is no epilogue vector loop. Could you update the es so it gets a vectorized epilogue?

https://github.com/llvm/llvm-project/pull/191186