[llvm] [VPlan] Support multiple F(Max|Min)Num reductions. (PR #161735)

[via llvm-commits]

================
@@ -118,23 +118,81 @@ define float @test_fmax_and_fmin(ptr %src.0, ptr %src.1, i64 %n) {
 ; CHECK-LABEL: define float @test_fmax_and_fmin(
 ; CHECK-SAME: ptr [[SRC_0:%.*]], ptr [[SRC_1:%.*]], i64 [[N:%.*]]) {
 ; CHECK-NEXT:  [[ENTRY:.*]]:
-; CHECK-NEXT:    br label %[[LOOP:.*]]
-; CHECK:       [[LOOP]]:
-; CHECK-NEXT:    [[IV:%.*]] = phi i64 [ 0, %[[ENTRY]] ], [ [[IV_NEXT:%.*]], %[[LOOP]] ]
-; CHECK-NEXT:    [[MIN:%.*]] = phi float [ 0.000000e+00, %[[ENTRY]] ], [ [[MIN_NEXT:%.*]], %[[LOOP]] ]
-; CHECK-NEXT:    [[MAX:%.*]] = phi float [ 0.000000e+00, %[[ENTRY]] ], [ [[MAX_NEXT:%.*]], %[[LOOP]] ]
+; CHECK-NEXT:    [[MIN_ITERS_CHECK:%.*]] = icmp ult i64 [[N]], 8
+; CHECK-NEXT:    br i1 [[MIN_ITERS_CHECK]], label %[[SCALAR_PH:.*]], label %[[VECTOR_PH:.*]]
+; CHECK:       [[VECTOR_PH]]:
+; CHECK-NEXT:    [[N_MOD_VF:%.*]] = urem i64 [[N]], 8
+; CHECK-NEXT:    [[N_VEC:%.*]] = sub i64 [[N]], [[N_MOD_VF]]
+; CHECK-NEXT:    br label %[[VECTOR_BODY:.*]]
+; CHECK:       [[VECTOR_BODY]]:
+; CHECK-NEXT:    [[IV:%.*]] = phi i64 [ 0, %[[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], %[[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[VEC_PHI:%.*]] = phi <4 x float> [ zeroinitializer, %[[VECTOR_PH]] ], [ [[TMP6:%.*]], %[[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[VEC_PHI1:%.*]] = phi <4 x float> [ zeroinitializer, %[[VECTOR_PH]] ], [ [[TMP7:%.*]], %[[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[VEC_PHI2:%.*]] = phi <4 x float> [ zeroinitializer, %[[VECTOR_PH]] ], [ [[TMP4:%.*]], %[[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[VEC_PHI3:%.*]] = phi <4 x float> [ zeroinitializer, %[[VECTOR_PH]] ], [ [[TMP5:%.*]], %[[VECTOR_BODY]] ]
 ; CHECK-NEXT:    [[GEP_SRC_0:%.*]] = getelementptr inbounds nuw float, ptr [[SRC_0]], i64 [[IV]]
 ; CHECK-NEXT:    [[GEP_SRC_1:%.*]] = getelementptr inbounds nuw float, ptr [[SRC_1]], i64 [[IV]]
-; CHECK-NEXT:    [[L_0:%.*]] = load float, ptr [[GEP_SRC_0]], align 4
-; CHECK-NEXT:    [[L_1:%.*]] = load float, ptr [[GEP_SRC_1]], align 4
+; CHECK-NEXT:    [[TMP2:%.*]] = getelementptr inbounds nuw float, ptr [[GEP_SRC_0]], i32 4
+; CHECK-NEXT:    [[WIDE_LOAD:%.*]] = load <4 x float>, ptr [[GEP_SRC_0]], align 4
+; CHECK-NEXT:    [[WIDE_LOAD4:%.*]] = load <4 x float>, ptr [[TMP2]], align 4
+; CHECK-NEXT:    [[TMP3:%.*]] = getelementptr inbounds nuw float, ptr [[GEP_SRC_1]], i32 4
+; CHECK-NEXT:    [[WIDE_LOAD5:%.*]] = load <4 x float>, ptr [[GEP_SRC_1]], align 4
+; CHECK-NEXT:    [[WIDE_LOAD6:%.*]] = load <4 x float>, ptr [[TMP3]], align 4
+; CHECK-NEXT:    [[TMP4]] = call <4 x float> @llvm.maxnum.v4f32(<4 x float> [[VEC_PHI2]], <4 x float> [[WIDE_LOAD]])
+; CHECK-NEXT:    [[TMP5]] = call <4 x float> @llvm.maxnum.v4f32(<4 x float> [[VEC_PHI3]], <4 x float> [[WIDE_LOAD4]])
+; CHECK-NEXT:    [[TMP6]] = call <4 x float> @llvm.minnum.v4f32(<4 x float> [[VEC_PHI]], <4 x float> [[WIDE_LOAD5]])
+; CHECK-NEXT:    [[TMP7]] = call <4 x float> @llvm.minnum.v4f32(<4 x float> [[VEC_PHI1]], <4 x float> [[WIDE_LOAD6]])
+; CHECK-NEXT:    [[INDEX_NEXT]] = add nuw i64 [[IV]], 8
+; CHECK-NEXT:    [[TMP8:%.*]] = fcmp uno <4 x float> [[WIDE_LOAD5]], [[WIDE_LOAD5]]
+; CHECK-NEXT:    [[TMP9:%.*]] = fcmp uno <4 x float> [[WIDE_LOAD6]], [[WIDE_LOAD6]]
+; CHECK-NEXT:    [[TMP14:%.*]] = fcmp uno <4 x float> [[WIDE_LOAD]], [[WIDE_LOAD]]
+; CHECK-NEXT:    [[TMP15:%.*]] = fcmp uno <4 x float> [[WIDE_LOAD4]], [[WIDE_LOAD4]]
----------------
ayalz wrote:

TODO - Would be nice to fold pairs together into:
```suggestion
; CHECK-NEXT:    [[TMP15:%.*]] = fcmp uno <4 x float> [[WIDE_LOAD]], [[WIDE_LOAD4]]
```


https://github.com/llvm/llvm-project/pull/161735