[llvm] [BasicAA] Add Vscale GEP decomposition on variable index (PR #69152)

[David Green via llvm-commits]

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@@ -1180,10 +1259,17 @@ AliasResult BasicAAResult::aliasGEP(
     else
       GCD = APIntOps::GreatestCommonDivisor(GCD, ScaleForGCD.abs());
 
-    ConstantRange CR = computeConstantRange(Index.Val.V, /* ForSigned */ false,
-                                            true, &AC, Index.CxtI);
-    KnownBits Known =
-        computeKnownBits(Index.Val.V, DL, 0, &AC, Index.CxtI, DT);
+    // FIXME: This could be expanded to use a more precise range for vscale.
+    ConstantRange CR =
+        Index.IsVScale
+            ? ConstantRange::getNonEmpty(
+                  APInt(OffsetRange.getBitWidth(), 1),
+                  APInt::getMaxValue(OffsetRange.getBitWidth()))
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davemgreen wrote:

We were trying to keep the first version simpler, getting the basics working without vscale range before adding it in the future.

https://github.com/llvm/llvm-project/pull/69152