From 9476d4543f4336a66308e55f722b0b0b2bd69dd2 Mon Sep 17 00:00:00 2001
From: Yong He <yonghe@outlook.com>
Date: Thu, 16 Mar 2023 23:46:14 -0700
Subject: Fix Phi simplification bug. (#2710)

* Fix Phi simplification bug.

* Fix up.

* Fix.

* Fix.

* Fix.

* Fix.

* Fix.

* Fix test.

* Fix test.

---------

Co-authored-by: Yong He <yhe@nvidia.com>
---
 source/slang/slang-ir-peephole.cpp | 38 ++++++++++++++++++++++++++++++++++----
 1 file changed, 34 insertions(+), 4 deletions(-)

(limited to 'source/slang/slang-ir-peephole.cpp')

diff --git a/source/slang/slang-ir-peephole.cpp b/source/slang/slang-ir-peephole.cpp
index 5d5a41726..65b5d2f45 100644
--- a/source/slang/slang-ir-peephole.cpp
+++ b/source/slang/slang-ir-peephole.cpp
@@ -1,6 +1,8 @@
 #include "slang-ir-peephole.h"
 #include "slang-ir-inst-pass-base.h"
 #include "slang-ir-sccp.h"
+#include "slang-ir-dominators.h"
+#include "slang-ir-util.h"
 
 namespace Slang
 {
@@ -290,6 +292,9 @@ struct PeepholeContext : InstPassBase
         return false;
     }
 
+    RefPtr<IRDominatorTree> domTree;
+    IRGlobalValueWithCode* domTreeFunc = nullptr;
+
     void processInst(IRInst* inst)
     {
         if (as<IRGlobalValueWithCode>(inst))
@@ -679,9 +684,35 @@ struct PeepholeContext : InstPassBase
                 {
                     if (inst->hasUses())
                     {
-                        inst->replaceUsesWith(argValue);
-                        // Never remove param inst.
-                        changed = true;
+                        // Is argValue a global constant?
+                        if (isChildInstOf(inst, argValue->getParent()))
+                        {
+                            inst->replaceUsesWith(argValue);
+                            // Never remove param inst.
+                            changed = true;
+                        }
+                        else
+                        {
+                            // If argValue is defined locally,
+                            // we can replace only if argVal dominates inst.
+                            auto parentFunc = getParentFunc(inst);
+                            if (!parentFunc)
+                                break;
+                            if (domTreeFunc != parentFunc)
+                            {
+                                domTree = computeDominatorTree(parentFunc);
+                                domTreeFunc = parentFunc;
+                            }
+                            if (!domTree)
+                                break;
+
+                            if (domTree->dominates(argValue, inst))
+                            {
+                                inst->replaceUsesWith(argValue);
+                                // Never remove param inst.
+                                changed = true;
+                            }
+                        }
                     }
                 }
             }
@@ -694,7 +725,6 @@ struct PeepholeContext : InstPassBase
     bool processFunc(IRInst* func)
     {
         bool result = false;
-
         for (;;)
         {
             changed = false;
-- 
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