[clang] [HLSL] add support for HLSLAggregateSplatCast and HLSLElementwiseCast to constant expression evaluator (PR #164700)

[Sarah Spall via cfe-commits]

================
@@ -0,0 +1,91 @@
+// RUN: %clang_cc1 -triple dxil-pc-shadermodel6.6-library -finclude-default-header -fnative-half-type -std=hlsl202x -verify %s
+
+// expected-no-diagnostics
+
+struct Base {
+  double D;
+  uint64_t2 U;
+  int16_t I : 5;
+  uint16_t I2: 5;
+};
+
+struct R : Base {
+  int G : 10;
+  int : 30;
+  float F;
+};
+
+struct B1 {
+  float A;
+  float B;
+};
+
+struct B2 : B1 {
+  int C;
+  int D;
+  bool BB;
+};
+
+export void fn() {
+  _Static_assert(((float4)(int[6]){1,2,3,4,5,6}).x == 1.0, "Woo!");
+
+  // This compiling successfully verifies that the array constant expression
+  // gets truncated to a float at compile time for instantiation via the
+  // flat cast
+  _Static_assert(((int)(int[2]){1,2}) == 1, "Woo!");
+
+  // truncation tests
+  // result type int
+  // truncate from struct
+  constexpr B1 SB1 = {1.0, 3.0};
+  constexpr float Blah = SB1.A;
----------------
spall wrote:

This was added for debugging reasons and meant to be deleted.

https://github.com/llvm/llvm-project/pull/164700