Basic IR support for `static const` globals (#404)

* Basic IR support for `static const` globals

Our strategy for lowering global *variables* can fall back to putting their initialization into a function, but that isn't really appropriate for global constants (it also isn't appropriate for arrays, but we'll need to deal with that seaprately).

This change adds a distinct case for global constants (rather than treating them as variables), and forces the emission logic to always emit them as a single expression.
Doing this makes assumptions about how the IR for these constants gets emitted (and what optimziations might do to it).
In order to make things work, I had to switch the handling of initializer-list expressions to not be lowered via temporaries and mutation (since that isn't a good fit for reverting to a single expression).

I've added a single test case to ensure that this works in the simplest scenario. My next priority will be to see if this unblocks my work in Falcor.

* Fixup: bug fixes

1 files changed, 23 insertions, 0 deletions

diff --git a/tests/compute/static-const-array.slang b/tests/compute/static-const-array.slang
new file mode 100644
index 000000000..242cfb096
--- /dev/null
+++ b/tests/compute/static-const-array.slang
@@ -0,0 +1,23 @@
+// static-const-array.slang
+
+//TEST(compute):COMPARE_COMPUTE_EX:-slang -compute
+//TEST_DISABLED(compute, vulkan):COMPARE_COMPUTE_EX:-vk -compute
+
+
+//TEST_INPUT:ubuffer(data=[0 0 0 0], stride=4):dxbinding(0),glbinding(0),out
+RWStructuredBuffer<int> outputBuffer;
+
+static const int kArray[] = { 16, 1, 32, 2 };
+
+int test(int val)
+{
+	return kArray[val];
+}
+
+[numthreads(4, 1, 1)]
+void computeMain(uint3 tid : SV_DispatchThreadID)
+{
+	int inVal = tid.x;
+	int outVal = test(inVal);
+	outputBuffer[inVal] = outVal;
+}
\ No newline at end of file