Keep const-ness in generic functions (#4028)

* Keep const-ness in generic functions

Closes #3834

The issue was that "const" variables inside of generic functions became
non-const variables.  This issue prevented some of GLSL texture
functions from being called inside of generic functions.

When `propagateConstExpr()` iterates the global functions, the generic
functions had to be handled little differently. This commit allows the
iteration to happen for the generic functions.

* Adding an explantion of the test as a comment

1 files changed, 33 insertions, 0 deletions

diff --git a/tests/bugs/gh-3834.slang b/tests/bugs/gh-3834.slang
new file mode 100644
index 000000000..1f0b2d3ba
--- /dev/null
+++ b/tests/bugs/gh-3834.slang
@@ -0,0 +1,33 @@
+//TEST:SIMPLE(filecheck=CHECK): -stage compute -entry computeMain -target glsl -allow-glsl
+//TEST:SIMPLE(filecheck=CHECK): -stage compute -entry computeMain -target glsl -allow-glsl -DUSE_GENERIC
+
+// This tests an issue that "const" variable was losing the
+// const-ness when they are in a generic function
+
+uniform sampler2D uniform_sampler2D;
+RWStructuredBuffer<float> outputBuffer;
+
+#ifdef USE_GENERIC
+__generic<T:__BuiltinArithmeticType>
+#endif
+vec4 MyFunc()
+{
+    //CHECK: const ivec2 offset0
+    //CHECK: const ivec2 offset1
+    const ivec2 offset0 = ivec2(0,0);
+    const ivec2 offset1 = ivec2(1,1);
+    const ivec2[4] offsets = { offset0, offset0, offset1, offset1 };
+    return textureGatherOffsets(uniform_sampler2D, vec2(0), offsets);
+}
+
+[numthreads(4, 1, 1)]
+void computeMain(uint3 dispatchThreadID : SV_DispatchThreadID)
+{
+#ifdef USE_GENERIC
+    vec4 result = MyFunc<float>();
+#else
+    vec4 result = MyFunc();
+#endif
+
+    outputBuffer[0] = result[0];
+}