From 9f5de6dadcdb9922ad8c8135a29e4abccec11671 Mon Sep 17 00:00:00 2001
From: Michael Kuperstein <michael.m.kuperstein@intel.com>
Date: Tue, 28 May 2013 08:17:48 +0000
Subject: Make BasicAliasAnalysis recognize the fact a noalias argument cannot
 alias another argument, even if the other argument is not itself marked
 noalias.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@182755 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Analysis/BasicAliasAnalysis.cpp | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

(limited to 'lib/Analysis/BasicAliasAnalysis.cpp')

diff --git a/lib/Analysis/BasicAliasAnalysis.cpp b/lib/Analysis/BasicAliasAnalysis.cpp
index f8509dd070..f20e83e911 100644
--- a/lib/Analysis/BasicAliasAnalysis.cpp
+++ b/lib/Analysis/BasicAliasAnalysis.cpp
@@ -142,6 +142,17 @@ static bool isObjectSize(const Value *V, uint64_t Size,
   return ObjectSize != AliasAnalysis::UnknownSize && ObjectSize == Size;
 }
 
+/// isIdentifiedFunctionLocal - Return true if V is umabigously identified
+/// at the function-level. Different IdentifiedFunctionLocals can't alias.
+/// Further, an IdentifiedFunctionLocal can not alias with any function
+/// arguments other than itself, which is not neccessarily true for
+/// IdentifiedObjects.
+static bool isIdentifiedFunctionLocal(const Value *V)
+{
+  return isa<AllocaInst>(V) || isNoAliasCall(V) || isNoAliasArgument(V);
+}
+
+
 //===----------------------------------------------------------------------===//
 // GetElementPtr Instruction Decomposition and Analysis
 //===----------------------------------------------------------------------===//
@@ -1205,10 +1216,10 @@ BasicAliasAnalysis::aliasCheck(const Value *V1, uint64_t V1Size,
         (isa<Constant>(O2) && isIdentifiedObject(O1) && !isa<Constant>(O1)))
       return NoAlias;
 
-    // Arguments can't alias with local allocations or noalias calls
-    // in the same function.
-    if (((isa<Argument>(O1) && (isa<AllocaInst>(O2) || isNoAliasCall(O2))) ||
-         (isa<Argument>(O2) && (isa<AllocaInst>(O1) || isNoAliasCall(O1)))))
+    // Function arguments can't alias with things that are known to be
+    // unambigously identified at the function level.
+    if ((isa<Argument>(O1) && isIdentifiedFunctionLocal(O2)) ||
+        (isa<Argument>(O2) && isIdentifiedFunctionLocal(O1)))
       return NoAlias;
 
     // Most objects can't alias null.
-- 
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