[clang] [X86][Clang] Support constexpr evaluation of cvtpd2ps intrinsics (PR #169980)

[Simon Pilgrim via cfe-commits]

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@@ -166,7 +166,7 @@ let Features = "sse2", Attributes = [NoThrow] in {
   def movnti : X86Builtin<"void(int *, int)">;
 }
 
-let Features = "sse2", Attributes = [NoThrow, Const, RequiredVectorWidth<128>] in {
+let Features = "sse2", Attributes = [NoThrow, Const, Constexpr, RequiredVectorWidth<128>] in {
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RKSimon wrote:

Don't update all these builtins to constexpr - find an existing "[NoThrow, Const, Constexpr, RequiredVectorWidth<128>]" block and move the cvtpd2ps def - same for the other pd2ps defs.

https://github.com/llvm/llvm-project/pull/169980