From 406bfa3e21e8fab3deab240c30c763e78eddf2f5 Mon Sep 17 00:00:00 2001
From: Christopher Lamb <christopher.lamb@gmail.com>
Date: Thu, 2 Aug 2007 01:18:14 +0000
Subject: [PATCH] Teach BasicAA about noalias parameter attributes, but do it
 correctly this time.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@40711 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Analysis/BasicAliasAnalysis.cpp           | 32 ++++++++++++++++++-
 .../BasicAA/2007-08-01-NoAliasAndCalls.ll     | 10 ++++++
 .../BasicAA/2007-08-01-NoAliasAndGEP.ll       | 17 ++++++++++
 3 files changed, 58 insertions(+), 1 deletion(-)
 create mode 100644 test/Analysis/BasicAA/2007-08-01-NoAliasAndCalls.ll
 create mode 100644 test/Analysis/BasicAA/2007-08-01-NoAliasAndGEP.ll

diff --git a/lib/Analysis/BasicAliasAnalysis.cpp b/lib/Analysis/BasicAliasAnalysis.cpp
index 580f7e5d9e4..39f232e3e56 100644
--- a/lib/Analysis/BasicAliasAnalysis.cpp
+++ b/lib/Analysis/BasicAliasAnalysis.cpp
@@ -18,6 +18,7 @@
 #include "llvm/Constants.h"
 #include "llvm/DerivedTypes.h"
 #include "llvm/Function.h"
+#include "llvm/ParameterAttributes.h"
 #include "llvm/GlobalVariable.h"
 #include "llvm/Instructions.h"
 #include "llvm/Pass.h"
@@ -260,6 +261,21 @@ BasicAliasAnalysis::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
   return AliasAnalysis::getModRefInfo(CS, P, Size);
 }
 
+static bool isNoAliasArgument(const Argument *Arg) {
+  const Function *Func = Arg->getParent();
+  const ParamAttrsList *Attr = Func->getFunctionType()->getParamAttrs();
+  if (Attr) {
+    unsigned Idx = 1;
+    for (Function::const_arg_iterator I = Func->arg_begin(), 
+          E = Func->arg_end(); I != E; ++I, ++Idx) {
+      if (&(*I) == Arg && 
+           Attr->paramHasAttr(Idx, ParamAttr::NoAlias))
+        return true;
+    }
+  }
+  return false;
+}
+
 // alias - Provide a bunch of ad-hoc rules to disambiguate in common cases, such
 // as array references.  Note that this function is heavily tail recursive.
 // Hopefully we have a smart C++ compiler.  :)
@@ -298,10 +314,24 @@ BasicAliasAnalysis::alias(const Value *V1, unsigned V1Size,
       if (isa<Argument>(O1)) {
         // Incoming argument cannot alias locally allocated object!
         if (isa<AllocationInst>(O2)) return NoAlias;
+        
+        // If they are two different objects, and one is a noalias argument
+        // then they do not alias.
+        if (O1 != O2 && isNoAliasArgument(cast<Argument>(O1)))
+          return NoAlias;
+          
         // Otherwise, nothing is known...
-      } else if (isa<Argument>(O2)) {
+      } 
+      
+      if (isa<Argument>(O2)) {
         // Incoming argument cannot alias locally allocated object!
         if (isa<AllocationInst>(O1)) return NoAlias;
+        
+        // If they are two different objects, and one is a noalias argument
+        // then they do not alias.
+        if (O1 != O2 && isNoAliasArgument(cast<Argument>(O2)))
+          return NoAlias;
+          
         // Otherwise, nothing is known...
       } else if (O1 != O2) {
         // If they are two different objects, we know that we have no alias...
diff --git a/test/Analysis/BasicAA/2007-08-01-NoAliasAndCalls.ll b/test/Analysis/BasicAA/2007-08-01-NoAliasAndCalls.ll
new file mode 100644
index 00000000000..072bfd9fe9c
--- /dev/null
+++ b/test/Analysis/BasicAA/2007-08-01-NoAliasAndCalls.ll
@@ -0,0 +1,10 @@
+; RUN: llvm-as %s -o - | opt -basicaa -aa-eval -print-all-alias-modref-info -disable-output &| grep 'MayAlias:     i32* %y, i32* %x'
+
+declare i32* @unclear(i32* %a)
+
+define void @foo(i32* noalias %x) {
+  %y = call i32* @unclear(i32* %x)
+  store i32 0, i32* %x
+  store i32 0, i32* %y
+  ret void
+}
diff --git a/test/Analysis/BasicAA/2007-08-01-NoAliasAndGEP.ll b/test/Analysis/BasicAA/2007-08-01-NoAliasAndGEP.ll
new file mode 100644
index 00000000000..8cc9f061d93
--- /dev/null
+++ b/test/Analysis/BasicAA/2007-08-01-NoAliasAndGEP.ll
@@ -0,0 +1,17 @@
+; RUN: llvm-as %s -o - | opt -basicaa -aa-eval -print-all-alias-modref-info -disable-output &| grep '9 no alias'
+; RUN: llvm-as %s -o - | opt -basicaa -aa-eval -print-all-alias-modref-info -disable-output &| grep '6 may alias'
+; RUN: llvm-as %s -o - | opt -basicaa -aa-eval -print-all-alias-modref-info -disable-output &| grep 'MayAlias:     i32* %pj, i32* %pi'
+
+define void @foo(i32* noalias %p, i32* noalias %q, i32 %i, i32 %j) {
+  %pi = getelementptr i32* %p, i32 %i
+  %qi = getelementptr i32* %q, i32 %i
+  %pj = getelementptr i32* %p, i32 %j
+  %qj = getelementptr i32* %q, i32 %j
+  store i32 0, i32* %p
+  store i32 0, i32* %pi
+  store i32 0, i32* %pj
+  store i32 0, i32* %q
+  store i32 0, i32* %qi
+  store i32 0, i32* %qj
+  ret void
+}
-- 
2.34.1