[llvm] [BasicAA] Compute minimal access extents lazily (PR #226931)

[Dávid Bolvanský via llvm-commits]

https://github.com/davidbolvansky updated https://github.com/llvm/llvm-project/pull/226931

>From 890d25ef723216e1f7280f2754b34cf537ec919b Mon Sep 17 00:00:00 2001
From: David Bolvansky <david.bolvansky at gmail.com>
Date: Mon, 28 Sep 2026 10:15:24 +0200
Subject: [PATCH] BasicAA: Compute minimal access extents lazily

---
 llvm/lib/Analysis/BasicAliasAnalysis.cpp | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/llvm/lib/Analysis/BasicAliasAnalysis.cpp b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
index fd9a7bb935170..52a46a3fe5a4b 100644
--- a/llvm/lib/Analysis/BasicAliasAnalysis.cpp
+++ b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
@@ -120,8 +120,12 @@ static std::optional<TypeSize> getObjectSize(const Value *V,
 /// Returns true if we can prove that the object specified by V is smaller than
 /// Size. Bails out early unless the root object is passed as the first
 /// parameter.
-static bool isObjectSmallerThan(const Value *V, TypeSize Size,
-                                const DataLayout &DL,
+static TypeSize getMinimalExtentFrom(const Value &V,
+                                     const LocationSize &LocSize,
+                                     const DataLayout &DL, bool NullIsValidLoc);
+
+static bool isObjectSmallerThan(const Value *V, const Value &OtherV,
+                                LocationSize OtherSize, const DataLayout &DL,
                                 const TargetLibraryInfo &TLI,
                                 bool NullIsValidLoc) {
   // Note that the meanings of the "object" are slightly different in the
@@ -147,6 +151,8 @@ static bool isObjectSmallerThan(const Value *V, TypeSize Size,
   if (!isIdentifiedObject(V))
     return false;
 
+  TypeSize Size = getMinimalExtentFrom(OtherV, OtherSize, DL, NullIsValidLoc);
+
   // This function needs to use the aligned object size because we allow
   // reads a bit past the end given sufficient alignment.
   std::optional<TypeSize> ObjectSize = getObjectSize(V, DL, TLI, NullIsValidLoc,
@@ -1615,12 +1621,8 @@ AliasResult BasicAAResult::aliasCheck(const Value *V1, LocationSize V1Size,
   // If the size of one access is larger than the entire object on the other
   // side, then we know such behavior is undefined and can assume no alias.
   bool NullIsValidLocation = NullPointerIsDefined(&F);
-  if ((isObjectSmallerThan(
-          O2, getMinimalExtentFrom(*V1, V1Size, DL, NullIsValidLocation), DL,
-          TLI, NullIsValidLocation)) ||
-      (isObjectSmallerThan(
-          O1, getMinimalExtentFrom(*V2, V2Size, DL, NullIsValidLocation), DL,
-          TLI, NullIsValidLocation)))
+  if (isObjectSmallerThan(O2, *V1, V1Size, DL, TLI, NullIsValidLocation) ||
+      isObjectSmallerThan(O1, *V2, V2Size, DL, TLI, NullIsValidLocation))
     return AliasResult::NoAlias;
 
   if (EnableSeparateStorageAnalysis) {