3 files changed, 45 insertions, 9 deletions

diff --git a/source/slang/ir-insts.h b/source/slang/ir-insts.h
index 05ccd76e7..6075c247c 100644
--- a/source/slang/ir-insts.h
+++ b/source/slang/ir-insts.h
@@ -712,7 +712,28 @@ struct IRBuilder
 
     IRWitnessTable* lookupWitnessTable(Name* mangledName);
     void registerWitnessTable(IRWitnessTable* table);
+
+        /// Create an empty basic block.
+        ///
+        /// The created block will not be inserted into the current
+        /// function; call `insertBlock()` to attach the block
+        /// at an appropriate point.
+        ///
     IRBlock* createBlock();
+
+        /// Insert a block into the current function.
+        ///
+        /// This attaches the given `block` to the current function,
+        /// and makes it the current block for
+        /// new instructions that get emitted.
+        ///
+    void insertBlock(IRBlock* block);
+
+        /// Emit a new block into the current function.
+        ///
+        /// This function is equivalent to using `createBlock()`
+        /// and then `insertBlock()`.
+        ///
     IRBlock* emitBlock();
 
     
diff --git a/source/slang/ir.cpp b/source/slang/ir.cpp
index 6e14edc1f..cc3350aef 100644
--- a/source/slang/ir.cpp
+++ b/source/slang/ir.cpp
@@ -2029,23 +2029,37 @@ namespace Slang
             getBasicBlockType());
     }
 
-    IRBlock* IRBuilder::emitBlock()
+    void IRBuilder::insertBlock(IRBlock* block)
     {
-        // Create a block
-        auto bb = createBlock();
-
         // If we are emitting into a function
         // (or another value with code), then
         // append the block to the function and
         // set this block as the new parent for
         // subsequent instructions we insert.
+        //
+        // TODO: This should probably insert the block
+        // after the current "insert into" block if
+        // there is one. Right now we are always
+        // adding the block to the end of the list,
+        // which is technically valid (the ordering
+        // of blocks doesn't affect the CFG topology),
+        // but some later passes might assume the ordering
+        // is significant in representing the intent
+        // of the original code.
+        //
         auto f = getFunc();
         if (f)
         {
-            f->addBlock(bb);
-            setInsertInto(bb);
+            f->addBlock(block);
+            setInsertInto(block);
         }
-        return bb;
+    }
+
+    IRBlock* IRBuilder::emitBlock()
+    {
+        auto block = createBlock();
+        insertBlock(block);
+        return block;
     }
 
     IRParam* IRBuilder::createParam(
diff --git a/source/slang/lower-to-ir.cpp b/source/slang/lower-to-ir.cpp
index 6cce469ea..806654ccb 100644
--- a/source/slang/lower-to-ir.cpp
+++ b/source/slang/lower-to-ir.cpp
@@ -4012,18 +4012,19 @@ struct DeclLoweringVisitor : DeclVisitor<DeclLoweringVisitor, LoweredValInfo>
             // generating the code we actually care about, back in the original function.
 
             auto builder = getBuilder();
+
             auto initBlock = builder->createBlock();
             auto afterBlock = builder->createBlock();
 
             builder->emitIfElse(getSimpleVal(context, boolVal), afterBlock, initBlock, afterBlock);
 
-            builder->setInsertInto(initBlock);
+            builder->insertBlock(initBlock);
             LoweredValInfo initVal = lowerLValueExpr(context, initExpr);
             assign(context, globalVal, initVal);
             assign(context, boolVal, LoweredValInfo::simple(builder->getBoolValue(true)));
             builder->emitBranch(afterBlock);
 
-            builder->setInsertInto(afterBlock);
+            builder->insertBlock(afterBlock);
         }
 
         irGlobal->moveToEnd();