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

[Joshua Batista via cfe-commits]

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@@ -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;
+  constexpr int X = (int)SB1;
+  _Static_assert(X == 1, "Woo!");
+
+  // result type float
+  // truncate from array
+  constexpr B1 Arr[2] = {4.0, 3.0, 2.0, 1.0};
+  constexpr float F = (float)Arr;
+  _Static_assert(F == 4.0, "Woo!");
+
+  // result type vector
+  // truncate from array of vector
+  constexpr int2 Arr2[2] = {5,6,7,8};
+  constexpr int2 I2 = (int2)Arr2;
+  _Static_assert(I2[0] == 5, "Woo!");
+  _Static_assert(I2[1] == 6, "Woo!");
+
+  // lhs and rhs are same "size" tests
+  
+  // result type vector from  array
+  constexpr int4 I4 = (int4)Arr;
+  _Static_assert(I4[0] == 4, "Woo!");
+  _Static_assert(I4[1] == 3, "Woo!");
+  _Static_assert(I4[2] == 2, "Woo!");
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bob80905 wrote:

Can we really guarantee that this memory won't be overwritten and these results will be consistent?

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