Run SSA pass to clean up temporary variables during generics lowering. (#1447)

* Run SSA pass to clean up generic temporary variables during lowering.

* Fix `undefined` emitting logic.

* revert dumpir control flag

* Defer fold decision of `undefined`  values after special case logic for GLSL and HLSL.

* Update expected test result.

* Manually update raygen.slang.glsl to minimize change.

* fix formatting

Co-authored-by: Tim Foley <tfoleyNV@users.noreply.github.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/source/slang/slang-emit-c-like.cpp b/source/slang/slang-emit-c-like.cpp
index 733811183..a3b11a908 100644
--- a/source/slang/slang-emit-c-like.cpp
+++ b/source/slang/slang-emit-c-like.cpp
@@ -1074,6 +1074,15 @@ bool CLikeSourceEmitter::shouldFoldInstIntoUseSites(IRInst* inst)
     if(inst->findDecoration<IRPreciseDecoration>())
         return false;
 
+    // In general, undefined value should be emitted as an uninitialized
+    // variable, so we shouldn't fold it.
+    // However, we cannot emit all undefined values a separate variable
+    // definition for certain types on certain targets (e.g. `out TriangleStream<T>`
+    // for GLSL), so we check this only after all those special cases are
+    // considered.
+    if (inst->op == kIROp_undefined)
+        return false;
+
     // Okay, at this point we know our instruction must have a single use.
     auto use = inst->firstUse;
     SLANG_ASSERT(use);