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.

1 files changed, 17 insertions, 1 deletions

diff --git a/source/slang/lower-to-ir.cpp b/source/slang/lower-to-ir.cpp
index 9e58d908b..c01059c61 100644
--- a/source/slang/lower-to-ir.cpp
+++ b/source/slang/lower-to-ir.cpp
@@ -2693,7 +2693,23 @@ struct DeclLoweringVisitor : DeclVisitor<DeclLoweringVisitor, LoweredValInfo>
 
         if( auto initExpr = decl->initExpr )
         {
-            // TODO: need to handle global with initializer!
+            IRBuilder subBuilderStorage = *getBuilder();
+            IRBuilder* subBuilder = &subBuilderStorage;
+
+            subBuilder->curFunc = irGlobal;
+
+            IRGenContext subContextStorage = *context;
+            IRGenContext* subContext = &subContextStorage;
+
+            subContext->irBuilder = subBuilder;
+
+            // TODO: set up a parent IR decl to put the instructions into
+
+            IRBlock* entryBlock = subBuilder->emitBlock();
+            subBuilder->curBlock = entryBlock;
+
+            LoweredValInfo initVal = lowerLValueExpr(subContext, initExpr);
+            subContext->irBuilder->emitReturn(getSimpleVal(subContext, initVal));
         }
 
         return globalVal;