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, 7 insertions, 1 deletions

diff --git a/source/slang/slang-ir-lower-generic-var.cpp b/source/slang/slang-ir-lower-generic-var.cpp
index 8799dea6b..936ed017f 100644
--- a/source/slang/slang-ir-lower-generic-var.cpp
+++ b/source/slang/slang-ir-lower-generic-var.cpp
@@ -79,6 +79,12 @@ namespace Slang
                 // have already been replaced with the pointer to that variable by now.
                 // So we don't need to do anything here.
             }
+            else if (valPtr->op == kIROp_undefined)
+            {
+                // We don't need to store an undef value.
+                storeInst->removeAndDeallocate();
+                return;
+            }
             else
             {
                 // If value does not come from another generic variable, then it must be
@@ -138,7 +144,7 @@ namespace Slang
 
         void processInst(IRInst* inst)
         {
-            if (inst->op == kIROp_Var || inst->op == kIROp_undefined)
+            if (inst->op == kIROp_Var)
             {
                 processVarInst(inst);
             }