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

[Farzon Lotfi 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)'
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farzonl wrote:

Is there a reason you have the checks after the declaration? Many of the other HLSL test cases have them before each function decl.

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