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

[Tex Riddell via cfe-commits]

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+// 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)'
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tex3d wrote:

Would using `CHECK-LABEL` be a bit better for these `Case*` checks?  I usually find it better for this purpose, since it prevents checks from before the label from erroneously matching content after the label which can make the subsequent error reporting harder to deal with.  But perhaps you can't use it due to restrictions on using regex within `CHECK-LABEL`, which IIRC was an issue?

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