SPIRV Legalization fixes. (#3479)

* Fix CFG legalization for SPIRV backend.

* Emit DepthReplacing execution mode.

* Fix do-while lowering.

---------

Co-authored-by: Yong He <yhe@nvidia.com>

1 files changed, 23 insertions, 4 deletions

diff --git a/source/slang/slang-lower-to-ir.cpp b/source/slang/slang-lower-to-ir.cpp
index f624b0baa..00db77511 100644
--- a/source/slang/slang-lower-to-ir.cpp
+++ b/source/slang/slang-lower-to-ir.cpp
@@ -5695,13 +5695,32 @@ struct StmtLoweringVisitor : StmtVisitor<StmtLoweringVisitor>
         {
             auto irCondition = getSimpleVal(context,
                 lowerRValueExpr(context, condExpr));
+            auto invCondition = builder->emitNot(irCondition->getDataType(), irCondition);
 
             // Now we want to `break` if the loop condition is false,
             // otherwise we will jump back to the head of the loop.
-            builder->emitLoopTest(
-                irCondition,
-                loopHead,
-                breakLabel);
+            // 
+            // We need to make sure not to reuse the break block of the loop as
+            // the break/merge block of the ifelse test.
+            // Therefore, we introduce a separate merge block for the loop test.
+            // 
+            // Emit the following structure:
+            // 
+            // [merge(mergeBlock)]
+            // if (cond) goto loopHead;
+            // else goto mergeBlock;
+            // 
+            // mergeBlock:
+            //   goto breakLabel;
+            auto mergeBlock = builder->emitBlock();
+            builder->emitBranch(loopHead);
+
+            builder->setInsertInto(testLabel);
+            builder->emitIfElse(
+                invCondition,
+                breakLabel,
+                mergeBlock,
+                mergeBlock);
         }
 
         // Finally we insert the label that a `break` will jump to