[llvm] [llvm] Support invariant.load on readonly intrinsics (PR #205916)

[Yingwei Zheng via llvm-commits]

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@@ -208,31 +210,47 @@ MemDepResult MemoryDependenceResults::getCallDependencyFrom(
     ModRefInfo MR = GetLocation(Inst, Loc, TLI);
     if (Loc.Ptr) {
       // A simple instruction.
-      if (isModOrRefSet(AA.getModRefInfo(Call, Loc)))
+      if (isModOrRefSet(AA.getModRefInfo(Call, Loc))) {
+        if (IsInvariantLoad)
+          continue;
         return MemDepResult::getClobber(Inst);
+      }
       continue;
     }
 
     if (auto *CallB = dyn_cast<CallBase>(Inst)) {
+      bool IsIdenticalReadOnlyCall = isReadOnlyCall && !isModSet(MR) &&
+                                     Call->isIdenticalToWhenDefined(CallB);
+
+      // An identical earlier invariant load-like call is an available value
+      // even if AA sees both calls as reading the same memory.
+      if (IsInvariantLoad && IsIdenticalReadOnlyCall)
+        return MemDepResult::getDef(Inst);
+
       // If these two calls do not interfere, look past it.
       if (isNoModRef(AA.getModRefInfo(Call, CallB))) {
         // If the two calls are the same, return Inst as a Def, so that
         // Call can be found redundant and eliminated.
-        if (isReadOnlyCall && !isModSet(MR) &&
-            Call->isIdenticalToWhenDefined(CallB))
+        if (IsIdenticalReadOnlyCall)
           return MemDepResult::getDef(Inst);
 
         // Otherwise if the two calls don't interact (e.g. CallB is readnone)
         // keep scanning.
         continue;
-      } else
+      } else if (IsInvariantLoad) {
+        continue;
+      } else {
         return MemDepResult::getClobber(Inst);
+      }
     }
 
     // If we could not obtain a pointer for the instruction and the instruction
     // touches memory then assume that this is a dependency.
-    if (isModOrRefSet(MR))
+    if (isModOrRefSet(MR)) {
+      if (IsInvariantLoad)
----------------
dtcxzyw wrote:

Is this path really reachable? Both load and intrinsic cases are handled above.


https://github.com/llvm/llvm-project/pull/205916