[InstCombine] Add more tests. NFC.

Author: dtcxzyw

llvm/test/Transforms/InstCombine/intrinsic-select.ll

@@ -358,3 +358,16 @@ define float @test_fabs_select_multiuse(i1 %cond, float %x) {
   %fabs = call float @llvm.fabs.f32(float %select)
   ret float %fabs
 }
+
+define float @test_fabs_select_multiuse_both_constant(i1 %cond, float %x) {
+; CHECK-LABEL: @test_fabs_select_multiuse_both_constant(
+; CHECK-NEXT:    [[SELECT:%.*]] = select i1 [[COND:%.*]], float -1.000000e+00, float -2.000000e+00
+; CHECK-NEXT:    call void @usef32(float [[SELECT]])
+; CHECK-NEXT:    [[FABS:%.*]] = call float @llvm.fabs.f32(float [[SELECT]])
+; CHECK-NEXT:    ret float [[FABS]]
+;
+  %select = select i1 %cond, float -1.0, float -2.0
+  call void @usef32(float %select)
+  %fabs = call float @llvm.fabs.f32(float %select)
+  ret float %fabs
+}