[SCEVAA] Enhance SCEVAAResult::alias() to handle two pointers with different pointer bases (#91453)

This patch enhances the SCEVAAResult::alias() interface to handle two
pointers with different pointer bases.

Before calling getMinusSCEV(), we firstly try to explicitly convert
these two pointers into ptrtoint expressions to do that.

Either both pointers are used with ptrtoint or neither, so we can't
end up with a ptr + int mix.

Author: csstormq

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
+}