[clang] [HLSL] Shore up floating point conversions (PR #90222)

[Chris B via cfe-commits]

================
@@ -0,0 +1,229 @@
+// RUN: %clang_cc1 -triple dxil-pc-shadermodel6.3-library -fnative-half-type -finclude-default-header -Wconversion -verify -o - %s
+// RUN: %clang_cc1 -triple dxil-pc-shadermodel6.3-library -fnative-half-type -finclude-default-header -ast-dump %s | FileCheck %s
+
+// This test verifies floating point type implicit conversion ranks for overload
+// resolution. In HLSL the built-in type ranks are half < float < double. This
+// applies to both scalar and vector types.
+
+// HLSL allows implicit truncation fo types, so it differentiates between
+// promotions (converting to larger types) and conversions (converting to
+// smaller types). Promotions are preferred over conversions. Promotions prefer
+// promoting to the next lowest type in the ranking order. Conversions prefer
+// converting to the next highest type in the ranking order.
+
+void HalfFloatDouble(double D);
+void HalfFloatDouble(float F);
+void HalfFloatDouble(half H);
+
+// CHECK: FunctionDecl {{.*}} used HalfFloatDouble 'void (double)'
+// CHECK: FunctionDecl {{.*}} used HalfFloatDouble 'void (float)'
+// CHECK: FunctionDecl {{.*}} used HalfFloatDouble 'void (half)'
+
+void FloatDouble(double D);
+void FloatDouble(float F);
+
+// CHECK: FunctionDecl {{.*}} used FloatDouble 'void (double)'
+// CHECK: FunctionDecl {{.*}} used FloatDouble 'void (float)'
+
+void HalfDouble(double D);
+void HalfDouble(half H);
+
+// CHECK: FunctionDecl {{.*}} used HalfDouble 'void (double)'
+// CHECK: FunctionDecl {{.*}} used HalfDouble 'void (half)'
+
+void HalfFloat(float F);
+void HalfFloat(half H);
+
+// CHECK: FunctionDecl {{.*}} used HalfFloat 'void (float)'
+// CHECK: FunctionDecl {{.*}} used HalfFloat 'void (half)'
+
+void Double(double D);
+void Float(float F);
+void Half(half H);
+
+// CHECK: FunctionDecl {{.*}} used Double 'void (double)'
+// CHECK: FunctionDecl {{.*}} used Float 'void (float)'
+// CHECK: FunctionDecl {{.*}} used Half 'void (half)'
+
+
+// Case 1: A function declared with overloads for half float and double types.
+//   (a) When called with half, it will resolve to half because half is an exact
+//   match.
+//   (b) When called with float it will resolve to float because float is an
+//   exact match.
+//   (c) When called with double it will resolve to double because it is an
+//   exact match.
+
+// CHECK: FunctionDecl {{.*}} Case1 'void (half, float, double)'
----------------
llvm-beanz wrote:

Yea, I wasn't relying on any match variables, which is what I usually use `CHECK-LABEL` for, but it could result in better output on error. I'll make that update.

https://github.com/llvm/llvm-project/pull/90222