SSA Register Allocation improvements. (#2857)

* SSA Register Allocation improvements.

* Fix.

* Rename `Use`->`UseOrPseudoUse`.

---------

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

1 files changed, 28 insertions, 0 deletions

diff --git a/source/slang/slang-ir-redundancy-removal.cpp b/source/slang/slang-ir-redundancy-removal.cpp
index 32c6abd39..37e8ba5bb 100644
--- a/source/slang/slang-ir-redundancy-removal.cpp
+++ b/source/slang/slang-ir-redundancy-removal.cpp
@@ -345,6 +345,34 @@ bool tryRemoveRedundantStore(IRGlobalValueWithCode* func, IRStore* store)
         store->removeAndDeallocate();
         return true;
     }
+
+    // A store can be removed if it is a store into the same var, and there are
+    // no side effects between the load of the var and the store of the var.
+    if (auto load = as<IRLoad>(store->getVal()))
+    {
+        if (load->getPtr() == store->getPtr())
+        {
+            if (load->getParent() == store->getParent())
+            {
+                bool valueMayChange = false;
+                for (auto inst = load->next; inst; inst = inst->next)
+                {
+                    if (inst == store)
+                        break;
+                    if (canInstHaveSideEffectAtAddress(func, inst, store->getPtr()))
+                    {
+                        valueMayChange = true;
+                        break;
+                    }
+                }
+                if (!valueMayChange)
+                {
+                    store->removeAndDeallocate();
+                    return true;
+                }
+            }
+        }
+    }
     return false;
 }