[llvm] [SimplifyCFG] Preserve common TBAA metadata when hoisting instructions. (PR #97158)

[Nikita Popov via llvm-commits]

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@@ -1807,17 +1878,39 @@ bool SimplifyCFGOpt::hoistCommonCodeFromSuccessors(Instruction *TI,
     SuccIterPairs.push_back(SuccIterPair(SuccItr, 0));
   }
 
-  // Check if only hoisting terminators is allowed. This does not add new
-  // instructions to the hoist location.
-  if (EqTermsOnly) {
-    // Skip any debug intrinsics, as they are free to hoist.
-    for (auto &SuccIter : make_first_range(SuccIterPairs)) {
-      auto *INonDbg = &*skipDebugIntrinsics(SuccIter);
-      if (!INonDbg->isTerminator())
-        return false;
+  if (AllInstsEqOnly) {
+    // Check if all instructions in the successor blocks match. This allows
+    // hoisting all instructions and removing the blocks we are hoisting from,
+    // so does not add any new instructions.
+    bool AllSame = true;
+    SmallVector<BasicBlock *> Succs = to_vector(successors(BB));
+    // Check if sizes and terminators of all successors match.
+    if (any_of(Succs, [&Succs](BasicBlock *Succ) {
+          Instruction *Term0 = Succs[0]->getTerminator();
+          Instruction *Term = Succ->getTerminator();
+          if (!Term->isSameOperationAs(Term0) ||
+              !equal(Term->operands(), Term0->operands()))
+            return true;
+          return Succs[0]->sizeWithoutDebug() != Succ->sizeWithoutDebug();
+        })) {
+      AllSame = false;
+    } else {
+      LockstepReverseIterator LRI(Succs);
+      while (LRI.isValid()) {
+        Instruction *I0 = (*LRI)[0];
+        if (any_of(*LRI, [I0](Instruction *I) {
+              return !areIdenticalUpToCommutativity(I0, I);
+            })) {
+          AllSame = false;
+          break;
+        }
----------------
nikic wrote:

The downside of this implementation is that it doesn't cover the case where one instruction uses the result of another (hoistable) instruction. But it's not needed for your use case...

https://github.com/llvm/llvm-project/pull/97158