[llvm] [GVN] MemorySSA for GVN: embed the memory state in symbolic expressions (PR #123218)

[Antonio Frighetto via llvm-commits]

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@@ -595,15 +608,48 @@ uint32_t GVNPass::ValueTable::lookupOrAddCall(CallInst *C) {
     return V;
   }
 
+  if (MSSA && AA->onlyReadsMemory(C)) {
+    Expression Exp = createExpr(C);
+    addMemoryStateToExp(C, Exp);
+    auto [V, _] = assignExpNewValueNum(Exp);
+    ValueNumbering[C] = V;
+    return V;
+  }
+
   ValueNumbering[C] = NextValueNumber;
   return NextValueNumber++;
 }
 
+/// Returns the value number for the specified load or store instruction.
+uint32_t GVNPass::ValueTable::lookupOrAddLoadStore(Instruction *I) {
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antoniofrighetto wrote:

I assume it was historically called this way as to align with the other routines. Though, indeed, `lookupOrAddCall` doesn't seem to do any lookup either, except for calling back `lookupOrAdd` indirectly for the call-site args (which also happens here in lookupOrAddLoadStore for the memory state). I don't think we should do any VN lookup here as already done in lookupOrAdd. Changed to `computeLoadStoreVN`, hopefully should make more sense (I think `lookupOrAddCall` could be renamed too...).

https://github.com/llvm/llvm-project/pull/123218