vendor/llvm-project/llvmorg-13.0.1-0-g75e33f71c2davendor/llvm-project/release-13.x

1 files changed, 20 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
index 4e3b18e805ee..71b3a411cc18 100644
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -2843,6 +2843,26 @@ static Instruction *tryToMoveFreeBeforeNullTest(CallInst &FI,
   }
   assert(FreeInstrBB->size() == 1 &&
          "Only the branch instruction should remain");
+
+  // Now that we've moved the call to free before the NULL check, we have to
+  // remove any attributes on its parameter that imply it's non-null, because
+  // those attributes might have only been valid because of the NULL check, and
+  // we can get miscompiles if we keep them. This is conservative if non-null is
+  // also implied by something other than the NULL check, but it's guaranteed to
+  // be correct, and the conservativeness won't matter in practice, since the
+  // attributes are irrelevant for the call to free itself and the pointer
+  // shouldn't be used after the call.
+  AttributeList Attrs = FI.getAttributes();
+  Attrs = Attrs.removeParamAttribute(FI.getContext(), 0, Attribute::NonNull);
+  Attribute Dereferenceable = Attrs.getParamAttr(0, Attribute::Dereferenceable);
+  if (Dereferenceable.isValid()) {
+    uint64_t Bytes = Dereferenceable.getDereferenceableBytes();
+    Attrs = Attrs.removeParamAttribute(FI.getContext(), 0,
+                                       Attribute::Dereferenceable);
+    Attrs = Attrs.addDereferenceableOrNullParamAttr(FI.getContext(), 0, Bytes);
+  }
+  FI.setAttributes(Attrs);
+
   return &FI;
 }