Fix a bug with hoisting 'IRVar' insts that are used outside the loop (#6446)

* Fix a bug with hoisting 'IRVar' insts that are used outside the loop

- We introduce a 'CheckpointObject' inst and use that to split loop state insts into two pieces (one for within-loop uses and one for outside-loop uses.
- This allows the two kinds of uses to be handled separately by the hoisting mechanism
- CheckpointObject is then lowered to a no-op after hoisting is complete.

* Update slang-ir-autodiff-primal-hoist.cpp

* Update slang-ir-autodiff-primal-hoist.cpp

1 files changed, 7 insertions, 0 deletions

diff --git a/source/slang/slang-ir.cpp b/source/slang/slang-ir.cpp
index fb274c4a0..3a7ace37d 100644
--- a/source/slang/slang-ir.cpp
+++ b/source/slang/slang-ir.cpp
@@ -5664,6 +5664,13 @@ IRInst* IRBuilder::emitDiscard()
     return inst;
 }
 
+IRInst* IRBuilder::emitCheckpointObject(IRInst* value)
+{
+    auto inst =
+        createInst<IRCheckpointObject>(this, kIROp_CheckpointObject, value->getFullType(), value);
+    addInst(inst);
+    return inst;
+}
 
 IRInst* IRBuilder::emitBranch(IRBlock* pBlock)
 {