[SCEVAA] Enhance SCEVAAResult::alias() to handle two pointers with different pointer bases

llvm/lib/Analysis/ScalarEvolutionAliasAnalysis.cpp

@@ -61,6 +61,19 @@ AliasResult SCEVAAResult::alias(const MemoryLocation &LocA,
                                  ? static_cast<uint64_t>(LocB.Size.getValue())
                                  : MemoryLocation::UnknownSize);
 
+    // Firstly, try to convert the two pointers into ptrtoint expressions to
+    // handle two pointers with different pointer bases.
+    // Either both pointers are used with ptrtoint or neither, so we can't end
+    // up with a ptr + int mix.
+    const SCEV *AInt =
+        SE.getPtrToIntExpr(AS, SE.getEffectiveSCEVType(AS->getType()));
+    const SCEV *BInt =
+        SE.getPtrToIntExpr(BS, SE.getEffectiveSCEVType(BS->getType()));
+    if (!isa<SCEVCouldNotCompute>(AInt) && !isa<SCEVCouldNotCompute>(BInt)) {
+      AS = AInt;
+      BS = BInt;
+    }
+
     // Compute the difference between the two pointers.
     const SCEV *BA = SE.getMinusSCEV(BS, AS);
 

llvm/test/Analysis/ScalarEvolution/scev-aa.ll

@@ -340,3 +340,29 @@ for.latch:
 for.end:
   ret void
 }
+
+; CHECK-LABEL: Function: test_different_pointer_bases_of_inttoptr: 2 pointers, 0 call sites
+; CHECK:   NoAlias:	<16 x i8>* %tmp5, <16 x i8>* %tmp7
+
+define void @test_different_pointer_bases_of_inttoptr() {
+entry:
+  br label %for.body
+
+for.body:
+  %tmp = phi i32 [ %next, %for.body ], [ 1, %entry ]
+  %tmp1 = shl nsw i32 %tmp, 1
+  %tmp2 = add nuw nsw i32 %tmp1, %tmp1
+  %tmp3 = mul nsw i32 %tmp2, 1408
+  %tmp4 = add nsw i32 %tmp3, 1408
+  %tmp5 = getelementptr inbounds i8, ptr inttoptr (i32 1024 to ptr), i32 %tmp1
+  %tmp6 = load <16 x i8>, ptr %tmp5, align 1
+  %tmp7 = getelementptr inbounds i8, ptr inttoptr (i32 4096 to ptr), i32 %tmp4
+  store <16 x i8> %tmp6, ptr %tmp7, align 1
+
+  %next = add i32 %tmp, 2
+  %exitcond = icmp slt i32 %next, 10
+  br i1 %exitcond, label %for.body, label %for.end
+
+for.end:
+  ret void
+}