IR: support global variable with initializers (#294)

The big change here is that the ability to contain basic blocks with instructions in them has been hoisted from `IRFunc` into a new base type `IRGlobalValueWithCode` shared with `IRGlobalVar`.
The basic blocks of a global variable define initialization logic for it; they can be looked at like a function that returns the initial value.

Places in the IR that used to assume functions contain all the code need to be updated, but so far I only handled the cloning step.

The emit logic currently handles an initializer for a global variable by outputting its logic as a separate function, and then having the variable call that function to initialize itself. This should be cleaned up over time so that we generate an ordinary expression whenever possible.

I also made the emit logic correctly label any global variable without a layout (that is, any that don't represent a shader parameter) as `static` so that the downstream HLSL compiler sees them as variables rather than parameters.

2 files changed, 27 insertions, 0 deletions

diff --git a/tests/compute/global-init.slang b/tests/compute/global-init.slang
new file mode 100644
index 000000000..909cdf7e6
--- /dev/null
+++ b/tests/compute/global-init.slang
@@ -0,0 +1,23 @@
+//TEST(compute):COMPARE_COMPUTE:-xslang -use-ir
+//TEST_INPUT:ubuffer(data=[0 1 2 3], stride=4):dxbinding(0),glbinding(0),out
+
+// Test that a global variable (not a shader parameter)
+// with an initializer works.
+
+static int gVar = 16;
+
+int test(int inVal)
+{
+	return inVal + gVar;
+}
+
+RWStructuredBuffer<int> outputBuffer : register(u0);
+
+[numthreads(4, 1, 1)]
+void computeMain(uint3 dispatchThreadID : SV_DispatchThreadID)
+{
+	uint tid = dispatchThreadID.x;
+	int inVal = outputBuffer[tid];
+	int outVal = test(inVal);
+	outputBuffer[tid] = outVal;
+}
\ No newline at end of file
diff --git a/tests/compute/global-init.slang.expected.txt b/tests/compute/global-init.slang.expected.txt
new file mode 100644
index 000000000..a0d427709
--- /dev/null
+++ b/tests/compute/global-init.slang.expected.txt
@@ -0,0 +1,4 @@
+10
+11
+12
+13