From ba13864483b696e7f8e2058c3a50b5d901f2213b Mon Sep 17 00:00:00 2001
From: Dan Gohman <gohman@apple.com>
Date: Wed, 20 Oct 2010 22:11:14 +0000
Subject: [PATCH] Factor out the main aliasing check into a separate function.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@116958 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Analysis/TypeBasedAliasAnalysis.cpp | 63 +++++++++++++++----------
 1 file changed, 39 insertions(+), 24 deletions(-)

diff --git a/lib/Analysis/TypeBasedAliasAnalysis.cpp b/lib/Analysis/TypeBasedAliasAnalysis.cpp
index 787db7351aa..5994ffd702f 100644
--- a/lib/Analysis/TypeBasedAliasAnalysis.cpp
+++ b/lib/Analysis/TypeBasedAliasAnalysis.cpp
@@ -103,6 +103,8 @@ namespace {
       return this;
     }
 
+    bool Aliases(const MDNode *A, const MDNode *B) const;
+
   private:
     virtual void getAnalysisUsage(AnalysisUsage &AU) const;
     virtual AliasResult alias(const Location &LocA, const Location &LocB);
@@ -125,27 +127,19 @@ TypeBasedAliasAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
   AliasAnalysis::getAnalysisUsage(AU);
 }
 
-AliasAnalysis::AliasResult
-TypeBasedAliasAnalysis::alias(const Location &LocA,
-                              const Location &LocB) {
-  if (!EnableTBAA)
-    return AliasAnalysis::alias(LocA, LocB);
-
-  // Get the attached MDNodes. If either value lacks a tbaa MDNode, we must
-  // be conservative.
-  const MDNode *AM = LocA.TBAATag;
-  if (!AM) return AliasAnalysis::alias(LocA, LocB);
-  const MDNode *BM = LocB.TBAATag;
-  if (!BM) return AliasAnalysis::alias(LocA, LocB);
-
+/// Aliases - Test whether the type represented by A may alias the
+/// type represented by B.
+bool
+TypeBasedAliasAnalysis::Aliases(const MDNode *A,
+                                const MDNode *B) const {
   // Keep track of the root node for A and B.
   TBAANode RootA, RootB;
 
   // Climb the tree from A to see if we reach B.
-  for (TBAANode T(AM); ; ) {
-    if (T.getNode() == BM)
+  for (TBAANode T(A); ; ) {
+    if (T.getNode() == B)
       // B is an ancestor of A.
-      return AliasAnalysis::alias(LocA, LocB);
+      return true;
 
     RootA = T;
     T = T.getParent();
@@ -154,10 +148,10 @@ TypeBasedAliasAnalysis::alias(const Location &LocA,
   }
 
   // Climb the tree from B to see if we reach A.
-  for (TBAANode T(BM); ; ) {
-    if (T.getNode() == AM)
+  for (TBAANode T(B); ; ) {
+    if (T.getNode() == A)
       // A is an ancestor of B.
-      return AliasAnalysis::alias(LocA, LocB);
+      return true;
 
     RootB = T;
     T = T.getParent();
@@ -167,13 +161,34 @@ TypeBasedAliasAnalysis::alias(const Location &LocA,
 
   // Neither node is an ancestor of the other.
   
-  // If they have the same root, then we've proved there's no alias.
-  if (RootA.getNode() == RootB.getNode())
-    return NoAlias;
-
   // If they have different roots, they're part of different potentially
   // unrelated type systems, so we must be conservative.
-  return AliasAnalysis::alias(LocA, LocB);
+  if (RootA.getNode() != RootB.getNode())
+    return true;
+
+  // If they have the same root, then we've proved there's no alias.
+  return false;
+}
+
+AliasAnalysis::AliasResult
+TypeBasedAliasAnalysis::alias(const Location &LocA,
+                              const Location &LocB) {
+  if (!EnableTBAA)
+    return AliasAnalysis::alias(LocA, LocB);
+
+  // Get the attached MDNodes. If either value lacks a tbaa MDNode, we must
+  // be conservative.
+  const MDNode *AM = LocA.TBAATag;
+  if (!AM) return AliasAnalysis::alias(LocA, LocB);
+  const MDNode *BM = LocB.TBAATag;
+  if (!BM) return AliasAnalysis::alias(LocA, LocB);
+
+  // If they may alias, chain to the next AliasAnalysis.
+  if (Aliases(AM, BM))
+    return AliasAnalysis::alias(LocA, LocB);
+
+  // Otherwise return a definitive result.
+  return NoAlias;
 }
 
 bool TypeBasedAliasAnalysis::pointsToConstantMemory(const Location &Loc) {
-- 
2.34.1