Fix IR lowering bug of do-while loops. (#3941)

2 files changed, 16 insertions, 5 deletions

diff --git a/source/slang/slang-ir-validate.cpp b/source/slang/slang-ir-validate.cpp
index 2868c9929..a4a2921fe 100644
--- a/source/slang/slang-ir-validate.cpp
+++ b/source/slang/slang-ir-validate.cpp
@@ -66,6 +66,7 @@ namespace Slang
         State state = kState_Initial;
 
         IRInst* prevChild = nullptr;
+        bool hasSeenTerminatorInst = false;
         for(auto child : parent->getDecorationsAndChildren() )
         {
             // We need to check the integrity of the parent/next/prev links of
@@ -105,7 +106,11 @@ namespace Slang
                 validate(context, !as<IRTerminatorInst>(child), child, "terminator must be last instruction in a block");
             }
 
-
+            if (as<IRTerminatorInst>(child))
+            {
+                validate(context, !hasSeenTerminatorInst, child, "block must not contain more than one terminator");
+                hasSeenTerminatorInst = true;
+            }
             prevChild = child;
         }
     }
diff --git a/source/slang/slang-lower-to-ir.cpp b/source/slang/slang-lower-to-ir.cpp
index 3f776c1a1..855bde6a6 100644
--- a/source/slang/slang-lower-to-ir.cpp
+++ b/source/slang/slang-lower-to-ir.cpp
@@ -5890,6 +5890,12 @@ struct StmtLoweringVisitor : StmtVisitor<StmtLoweringVisitor>
         {
             auto irCondition = getSimpleVal(context,
                 lowerRValueExpr(context, condExpr));
+
+            // One thing to be careful here is that lowering irCondition
+            // may create additional blocks due to short circuiting, so
+            // the block we are current inserting into is not necessarily
+            // the same as `testLabel`.
+            // 
             auto invCondition = builder->emitNot(irCondition->getDataType(), irCondition);
 
             // Now we want to `break` if the loop condition is false,
@@ -5907,15 +5913,15 @@ struct StmtLoweringVisitor : StmtVisitor<StmtLoweringVisitor>
             // 
             // mergeBlock:
             //   goto breakLabel;
-            auto mergeBlock = builder->emitBlock();
-            builder->emitBranch(loopHead);
-
-            builder->setInsertInto(testLabel);
+            auto mergeBlock = builder->createBlock();
             builder->emitIfElse(
                 invCondition,
                 breakLabel,
                 mergeBlock,
                 mergeBlock);
+
+            insertBlock(mergeBlock);
+            builder->emitBranch(loopHead);
         }
 
         // Finally we insert the label that a `break` will jump to