Add test case for x86 maxnum

Should be profitable on AVX2 but not SSE2

Author: lukel97

llvm/test/Transforms/VectorCombine/X86/intrinsic-scalarize.ll

@@ -0,0 +1,26 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt < %s -S -p vector-combine -mtriple=x86_64 -mattr=sse2 | FileCheck %s --check-prefixes=CHECK,SSE2
+; RUN: opt < %s -S -p vector-combine -mtriple=x86_64 -mattr=avx2 | FileCheck %s --check-prefixes=CHECK,AVX2
+
+define <2 x float> @maxnum(float %x, float %y) {
+; SSE2-LABEL: define <2 x float> @maxnum(
+; SSE2-SAME: float [[X:%.*]], float [[Y:%.*]]) #[[ATTR0:[0-9]+]] {
+; SSE2-NEXT:    [[X_INSERT:%.*]] = insertelement <2 x float> poison, float [[X]], i32 0
+; SSE2-NEXT:    [[Y_INSERT:%.*]] = insertelement <2 x float> poison, float [[Y]], i32 0
+; SSE2-NEXT:    [[V:%.*]] = call <2 x float> @llvm.maxnum.v2f32(<2 x float> [[X_INSERT]], <2 x float> [[Y_INSERT]])
+; SSE2-NEXT:    ret <2 x float> [[V]]
+;
+; AVX2-LABEL: define <2 x float> @maxnum(
+; AVX2-SAME: float [[X:%.*]], float [[Y:%.*]]) #[[ATTR0:[0-9]+]] {
+; AVX2-NEXT:    [[V_SCALAR:%.*]] = call float @llvm.maxnum.f32(float [[X]], float [[Y]])
+; AVX2-NEXT:    [[TMP1:%.*]] = call <2 x float> @llvm.maxnum.v2f32(<2 x float> poison, <2 x float> poison)
+; AVX2-NEXT:    [[V:%.*]] = insertelement <2 x float> [[TMP1]], float [[V_SCALAR]], i64 0
+; AVX2-NEXT:    ret <2 x float> [[V]]
+;
+  %x.insert = insertelement <2 x float> poison, float %x, i32 0
+  %y.insert = insertelement <2 x float> poison, float %y, i32 0
+  %v = call <2 x float> @llvm.maxnum(<2 x float> %x.insert, <2 x float> %y.insert)
+  ret <2 x float> %v
+}
+;; NOTE: These prefixes are unused and the list is autogenerated. Do not add tests below this line:
+; CHECK: {{.*}}