[llvm] [BasicAA] Handle scalable type sizes with constant offsets (PR #80445)

[Nikita Popov via llvm-commits]

================
@@ -1146,24 +1142,37 @@ AliasResult BasicAAResult::aliasGEP(
     if (!VLeftSize.hasValue())
       return AliasResult::MayAlias;
 
-    const uint64_t LSize = VLeftSize.getValue();
-    if (Off.ult(LSize)) {
-      // Conservatively drop processing if a phi was visited and/or offset is
-      // too big.
-      AliasResult AR = AliasResult::PartialAlias;
-      if (VRightSize.hasValue() && Off.ule(INT32_MAX) &&
-          (Off + VRightSize.getValue()).ule(LSize)) {
-        // Memory referenced by right pointer is nested. Save the offset in
-        // cache. Note that originally offset estimated as GEP1-V2, but
-        // AliasResult contains the shift that represents GEP1+Offset=V2.
-        AR.setOffset(-Off.getSExtValue());
-        AR.swap(Swapped);
+    const TypeSize LSize = VLeftSize.getValue();
+    if (!LSize.isScalable()) {
+      if (Off.ult(LSize)) {
+        // Conservatively drop processing if a phi was visited and/or offset is
+        // too big.
+        AliasResult AR = AliasResult::PartialAlias;
+        if (VRightSize.hasValue() && !VRightSize.isScalable() &&
+            Off.ule(INT32_MAX) && (Off + VRightSize.getValue()).ule(LSize)) {
+          // Memory referenced by right pointer is nested. Save the offset in
+          // cache. Note that originally offset estimated as GEP1-V2, but
+          // AliasResult contains the shift that represents GEP1+Offset=V2.
+          AR.setOffset(-Off.getSExtValue());
+          AR.swap(Swapped);
+        }
+        return AR;
       }
-      return AR;
+      return AliasResult::NoAlias;
+    } else {
+      // We can used the getVScaleRange to prove that Off >= (CR.upper * LSize).
----------------
nikic wrote:

```suggestion
      // We can use the getVScaleRange to prove that Off >= (CR.upper * LSize).
```

https://github.com/llvm/llvm-project/pull/80445