[PATCH] D115927: [AA] Correctly maintain the sign of PartiaAlias offset

[Momchil Velikov via Phabricator via llvm-commits]

chill created this revision.
chill added reviewers: dfukalov, nikic.
Herald added subscribers: jeroen.dobbelaere, hiraditya.
chill requested review of this revision.
Herald added a project: LLVM.
Herald added a subscriber: llvm-commits.

Preserve the invariant that offset reported in the case of a
`PartialAlias` between `Loc1` and `Loc2`, is such that `Loc1 + Offset = Loc2`, where
`Loc1` and `Loc2` are the first and the second argument, respectively, in alias queries.


https://reviews.llvm.org/D115927

Files:
  llvm/lib/Analysis/BasicAliasAnalysis.cpp
  llvm/unittests/Analysis/AliasAnalysisTest.cpp


Index: llvm/unittests/Analysis/AliasAnalysisTest.cpp
===================================================================
--- llvm/unittests/Analysis/AliasAnalysisTest.cpp
+++ llvm/unittests/Analysis/AliasAnalysisTest.cpp
@@ -333,6 +333,38 @@
   EXPECT_EQ(4, AR.getOffset());
 }
 
+// Check that swapping the order of parameters to `AA.alias()` changes offset
+// sign and that the sign is such that FirstLoc + Offset == SecondLoc.
+TEST_F(AliasAnalysisTest, PartialAliasOffsetSign) {
+  LLVMContext C;
+  SMDiagnostic Err;
+  std::unique_ptr<Module> M = parseAssemblyString(R"(
+    define void @f(i64* %p) {
+      %L1 = load i64, i64* %p
+      %p.i8 = bitcast i64* %p to i8*
+      %q = getelementptr i8,  i8* %p.i8, i32 1
+      %L2 = load i8, i8* %q
+      ret void
+    }
+  )", Err, C);
+
+  if (!M)
+    Err.print("PartialAliasOffsetSign", errs());
+
+  Function *F = M->getFunction("f");
+  const auto Loc1 = MemoryLocation::get(getInstructionByName(*F, "L1"));
+  const auto Loc2 = MemoryLocation::get(getInstructionByName(*F, "L2"));
+
+  auto &AA = getAAResults(*F);
+
+  auto AR = AA.alias(Loc1, Loc2);
+  EXPECT_EQ(AR, AliasResult::PartialAlias);
+  EXPECT_EQ(1, AR.getOffset());
+
+  AR = AA.alias(Loc2, Loc1);
+  EXPECT_EQ(AR, AliasResult::PartialAlias);
+  EXPECT_EQ(-1, AR.getOffset());
+}
 class AAPassInfraTest : public testing::Test {
 protected:
   LLVMContext C;
Index: llvm/lib/Analysis/BasicAliasAnalysis.cpp
===================================================================
--- llvm/lib/Analysis/BasicAliasAnalysis.cpp
+++ llvm/lib/Analysis/BasicAliasAnalysis.cpp
@@ -1699,6 +1699,7 @@
       return Result;
   } else if (const GEPOperator *GV2 = dyn_cast<GEPOperator>(V2)) {
     AliasResult Result = aliasGEP(GV2, V2Size, V1, V1Size, O2, O1, AAQI);
+    Result.swap();
     if (Result != AliasResult::MayAlias)
       return Result;
   }
@@ -1709,6 +1710,7 @@
       return Result;
   } else if (const PHINode *PN = dyn_cast<PHINode>(V2)) {
     AliasResult Result = aliasPHI(PN, V2Size, V1, V1Size, AAQI);
+    Result.swap();
     if (Result != AliasResult::MayAlias)
       return Result;
   }
@@ -1719,6 +1721,7 @@
       return Result;
   } else if (const SelectInst *S2 = dyn_cast<SelectInst>(V2)) {
     AliasResult Result = aliasSelect(S2, V2Size, V1, V1Size, AAQI);
+    Result.swap();
     if (Result != AliasResult::MayAlias)
       return Result;
   }


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