[PATCH] D51936: Fix a use-after-RAUW bug in large GEP splitting

[Krzysztof Pszeniczny via Phabricator via llvm-commits]

amharc updated this revision to Diff 170138.
amharc edited the summary of this revision.
amharc added a comment.

Updated the patch to manually merge vectors of  large GEP offsets when doing a RAUW of an invariant.group strip/launder intrinsic. This requires only handling keys and not values of the map, as values are always `GetElementPtr` instructions and not intrinsic calls.

I do not have the necessary level of understanding of CGP to determine if there are any other RAUWs there that need attention too, but so far I wasn't able to reproduce in cases that do not relate to invariant.group strips/launders.


https://reviews.llvm.org/D51936

Files:
  llvm/lib/CodeGen/CodeGenPrepare.cpp
  llvm/test/Transforms/CodeGenPrepare/AArch64/large-offset-gep.ll


Index: llvm/test/Transforms/CodeGenPrepare/AArch64/large-offset-gep.ll
===================================================================
--- llvm/test/Transforms/CodeGenPrepare/AArch64/large-offset-gep.ll
+++ llvm/test/Transforms/CodeGenPrepare/AArch64/large-offset-gep.ll
@@ -145,3 +145,31 @@
 while_end:
   ret void
 }
+
+declare i8* @llvm.strip.invariant.group.p0i8(i8*)
+
+define void @test_invariant_group(i32) {
+; CHECK-LABEL: test_invariant_group
+  br i1 undef, label %8, label %7
+
+; <label>:2:                                      ; preds = %8, %2
+  br i1 undef, label %2, label %7
+
+; <label>:3:                                      ; preds = %8
+  %4 = getelementptr inbounds i8, i8* %9, i32 40000
+  %5 = bitcast i8* %4 to i64*
+  br i1 undef, label %7, label %6
+
+; <label>:6:                                      ; preds = %3
+  store i64 1, i64* %5, align 8
+  br label %7
+
+; <label>:7:                                      ; preds = %6, %3, %2, %1
+  ret void
+
+; <label>:8:                                      ; preds = %1
+  %9 = call i8* @llvm.strip.invariant.group.p0i8(i8* nonnull undef)
+  %10 = icmp eq i32 %0, 0
+  br i1 %10, label %3, label %2
+}
+
Index: llvm/lib/CodeGen/CodeGenPrepare.cpp
===================================================================
--- llvm/lib/CodeGen/CodeGenPrepare.cpp
+++ llvm/lib/CodeGen/CodeGenPrepare.cpp
@@ -1721,11 +1721,22 @@
       return true;
     }
     case Intrinsic::launder_invariant_group:
-    case Intrinsic::strip_invariant_group:
-      II->replaceAllUsesWith(II->getArgOperand(0));
+    case Intrinsic::strip_invariant_group: {
+      Value *ArgVal = II->getArgOperand(0);
+      auto it = LargeOffsetGEPMap.find(II);
+      if (it != LargeOffsetGEPMap.end()) {
+          // Merge entries in LargeOffsetGEPMap to reflect the RAUW.
+          // Make sure not to have to deal with iterator invalidation
+          // after possibly adding ArgVal to LargeOffsetGEPMap.
+          auto GEPs = std::move(it->second);
+          LargeOffsetGEPMap[ArgVal].append(GEPs.begin(), GEPs.end());
+          LargeOffsetGEPMap.erase(II);
+      }
+
+      II->replaceAllUsesWith(ArgVal);
       II->eraseFromParent();
       return true;
-
+    }
     case Intrinsic::cttz:
     case Intrinsic::ctlz:
       // If counting zeros is expensive, try to avoid it.


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