[clang] [NFC] Cleanup and sort hlsl_intrinsics.h (PR #72414)

[David Peixotto via cfe-commits]

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@@ -11,557 +11,614 @@
 
 namespace hlsl {
 
-__attribute__((availability(shadermodel, introduced = 6.0)))
-__attribute__((clang_builtin_alias(__builtin_hlsl_wave_active_count_bits))) uint
-WaveActiveCountBits(bool bBit);
+// Note: Functions in this file are sorted alphabetically, then grouped by base
+// element type, and the element types are sorted by size, then singed integer,
+// unsigned integer and floating point. Keeping this ordering consistent will
+// help keep this file manageable as it grows.
 
+#define _HLSL_BUILTIN_ALIAS(builtin)                                           \
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dmpots wrote:

Is it ok to have macros that start with an underscore? I thought identifiers starting with _ are reserved in c/c++, but not sure about macros.

Also, since this is a header file should we undef them at the end? Not sure we expect others to use the macros themselves, but more of just an implementation detail of the header.

https://github.com/llvm/llvm-project/pull/72414