More control flow simplifications. (#2673)

* More control flow and Phi param simplifications.

* Fix.

* Fix gcc error.

* Fix.

* More IR cleanup.

* Fix bug in phi param dce + ifelse simplify.

* Propagate and DCE side-effect-free functions.

* Enhance CFG simplifcation to remove loops with no side effects.

* Fix.

* Fixes.

* Fix tests. Add [__AlwaysFoldIntoUseSite] for rayPayloadLocation.

* More cleanup.

* Fixes.

* Fix.

---------

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

1 files changed, 11 insertions, 1 deletions

diff --git a/source/slang/slang-emit-c-like.cpp b/source/slang/slang-emit-c-like.cpp
index c664449e5..7840dc450 100644
--- a/source/slang/slang-emit-c-like.cpp
+++ b/source/slang/slang-emit-c-like.cpp
@@ -1244,14 +1244,24 @@ bool CLikeSourceEmitter::shouldFoldInstIntoUseSites(IRInst* inst)
             return true;
     }
 
+    // Always hold if inst is a call into an [__alwaysFoldIntoUseSite] function.
+    if (auto call = as<IRCall>(inst))
+    {
+        auto callee = call->getCallee();
+        if (getResolvedInstForDecorations(callee)->findDecoration<IRAlwaysFoldIntoUseSiteDecoration>())
+        {
+            return true;
+        }
+    }
+
     // Having dealt with all of the cases where we *must* fold things
     // above, we can now deal with the more general cases where we
     // *should not* fold things.
-
     // Don't fold something with no users:
     if(!inst->hasUses())
         return false;
 
+
     // Don't fold something that has multiple users:
     if(inst->hasMoreThanOneUse())
         return false;