From 9d788d5db9d8e5ed0ac2c5659c3bc663ed66ddaa Mon Sep 17 00:00:00 2001
From: Yong He <yonghe@outlook.com>
Date: Wed, 13 Nov 2024 09:33:01 -0800
Subject: [PATCH] Fix regression caused by defer buffer load.

---
 source/slang/slang-ir-defer-buffer-load.cpp | 150 +-------------------
 1 file changed, 2 insertions(+), 148 deletions(-)

diff --git a/source/slang/slang-ir-defer-buffer-load.cpp b/source/slang/slang-ir-defer-buffer-load.cpp
index d1eb4b5e5c..fea73e7052 100644
--- a/source/slang/slang-ir-defer-buffer-load.cpp
+++ b/source/slang/slang-ir-defer-buffer-load.cpp
@@ -11,131 +11,15 @@ namespace Slang
 {
 struct DeferBufferLoadContext
 {
-    struct AccessChain
-    {
-        List<IRInst*> chain;
-        mutable HashCode64 hash = 0;
-
-        bool operator==(const AccessChain& rhs) const
-        {
-            ensureHash();
-            rhs.ensureHash();
-            if (hash != rhs.hash)
-                return false;
-            if (chain.getCount() != rhs.chain.getCount())
-                return false;
-            for (Index i = 0; i < chain.getCount(); i++)
-            {
-                if (chain[i] != rhs.chain[i])
-                    return false;
-            }
-            return true;
-        }
-        void ensureHash() const
-        {
-            if (hash == 0)
-            {
-                for (auto inst : chain)
-                {
-                    hash = combineHash(hash, Slang::getHashCode(inst));
-                }
-            }
-        }
-        HashCode64 getHashCode() const
-        {
-            ensureHash();
-            return hash;
-        }
-    };
-
     // Map an original SSA value to a pointer that can be used to load the value.
-    Dictionary<AccessChain, IRInst*> mapAccessChainToPtr;
     Dictionary<IRInst*, IRInst*> mapValueToPtr;
+
     // Map an ptr to its loaded value.
     Dictionary<IRInst*, IRInst*> mapPtrToValue;
 
     IRFunc* currentFunc = nullptr;
     IRDominatorTree* dominatorTree = nullptr;
 
-    // Find the block that is dominated by all dependent blocks, and is the earliest block that
-    // dominates the target block.
-    // This is the place where we can insert the load instruction such that all access chain
-    // operands are defined and the load can be made avaialble to the location of valueInst.
-    //
-    IRBlock* findEarliestDominatingBlock(IRInst* valueInst, List<IRBlock*>& dependentBlocks)
-    {
-        auto targetBlock = getBlock(valueInst);
-        while (targetBlock)
-        {
-            auto idom = dominatorTree->getImmediateDominator(targetBlock);
-            if (!idom)
-                break;
-            bool isValid = true;
-            for (auto block : dependentBlocks)
-            {
-                if (!dominatorTree->dominates(block, idom))
-                {
-                    isValid = false;
-                    break;
-                }
-            }
-            if (isValid)
-            {
-                targetBlock = idom;
-            }
-            else
-            {
-                break;
-            }
-        }
-        return targetBlock;
-    }
-
-    // Find the earliest instruction before which we can insert the load instruction such that
-    // all dependent instructions for the load address are defined, and the load can reach all
-    // locations where the address is available.
-    //
-    IRInst* findEarliestInsertionPoint(IRInst* valueInst, AccessChain& chain)
-    {
-        List<IRBlock*> dependentBlocks;
-        List<IRInst*> dependentInsts;
-        for (auto inst : chain.chain)
-        {
-            if (auto block = getBlock(inst))
-            {
-                dependentBlocks.add(block);
-                dependentInsts.add(inst);
-            }
-        }
-        auto targetBlock = findEarliestDominatingBlock(valueInst, dependentBlocks);
-        IRInst* insertBeforeInst =
-            targetBlock == getBlock(valueInst) ? valueInst : targetBlock->getTerminator();
-        for (;;)
-        {
-            auto prev = insertBeforeInst->getPrevInst();
-            if (!prev)
-                break;
-            bool valid = true;
-            for (auto inst : dependentInsts)
-            {
-                if (!dominatorTree->dominates(inst, prev) || inst == prev)
-                {
-                    valid = false;
-                    break;
-                }
-            }
-            if (valid)
-            {
-                insertBeforeInst = prev;
-            }
-            else
-            {
-                break;
-            }
-        }
-        return insertBeforeInst;
-    }
-
     // Ensure that for an original SSA value, we have formed a pointer that can be used to load the
     // value.
     IRInst* ensurePtr(IRInst* valueInst)
@@ -143,38 +27,9 @@ struct DeferBufferLoadContext
         IRInst* result = nullptr;
         if (mapValueToPtr.tryGetValue(valueInst, result))
             return result;
-        AccessChain chain;
-        IRInst* current = valueInst;
-        while (current)
-        {
-            bool processed = false;
-            switch (current->getOp())
-            {
-            case kIROp_GetElement:
-            case kIROp_FieldExtract:
-                chain.chain.add(current->getOperand(1));
-                current = current->getOperand(0);
-                processed = true;
-                break;
-            default:
-                break;
-            }
-            if (!processed)
-                break;
-        }
-        chain.chain.add(current);
-        chain.chain.reverse();
-        if (mapAccessChainToPtr.tryGetValue(chain, result))
-            return result;
 
-        // Find the proper place to insert the load instruction.
-        // This is the location where all operands of the access chain are defined.
-        // And is the earliest block so all possible uses of the value at access chain
-        // can be reached.
         IRBuilder b(valueInst);
-
-        auto insertBeforeInst = findEarliestInsertionPoint(valueInst, chain);
-        b.setInsertBefore(insertBeforeInst);
+        b.setInsertBefore(valueInst);
 
         switch (valueInst->getOp())
         {
@@ -205,7 +60,6 @@ struct DeferBufferLoadContext
         }
         if (result)
         {
-            mapAccessChainToPtr[chain] = result;
             mapValueToPtr[valueInst] = result;
         }
         return result;