Fix error when one constant is defined equal to another (#670)

* Fix error when one constant is defined equal to another

Fixes #666

When a user declares one constant (usually a `static const` variable) to be exactly equal to another by name:

```hlsl
static const a = 999;
static const b = a;
```

Then the IR-level representation of `b` is an `IRGlobalConstant` whose value expression is just a pointer to the definition of `a`.

The logic in `emitIRGlobalConstantInitializer()` was trying to always call `emitIRInstExpr` to emit the value of the constant as an expression, but that function only handles complex/compound expressions and not the case of simple named values (e.g., constants like `a`).

The intention is for code to call `emitIROperand()` instead, and let it decide whether to emit an expression or a named reference using its own decision-making. The `IRGlobalConstant` case really just wants to pass in the "mode" flag it uses to influence that decision-making, but shouldn't be working around it.

This change just replaces the `emitIRInstExp()` call with `emitIROpernad()` and adds a test case to confirm that this fixes the reported problem.

* Fixups for bugs in previous change

The first problem was that certain instruction ops were being special-cased to opt out of "folding" into expressions *before* we make the universal check to always fold when inside an initializer for a global constant.

The second problem is that the `emitIROperand()` logic was always putting expressions around sub-expressions, which breaks parsing when the sub-expression is an initializer list (`{...}`). This fixup is pretty much a hack, but will be something we can remove once we don't emit unncessary parentheses overall, which is a better fix.

1 files changed, 11 insertions, 0 deletions

diff --git a/tests/bugs/gh-666.slang b/tests/bugs/gh-666.slang
new file mode 100644
index 000000000..fa46d1de7
--- /dev/null
+++ b/tests/bugs/gh-666.slang
@@ -0,0 +1,11 @@
+// gh-666.slang
+
+//TEST:COMPARE_HLSL:-no-mangle -profile ps_5_0 -entry main
+
+static const uint foo = 1;
+static const uint bar = foo;
+
+float4 main() : SV_TARGET
+{
+	return bar;
+}