From 5e561bbd5dcedf5338e939ef8ead1eadd797240c Mon Sep 17 00:00:00 2001
From: Duncan Sands <baldrick@free.fr>
Date: Sun, 30 Sep 2012 07:30:10 +0000
Subject: [PATCH] Ignore apparent buffer overruns on external or weak globals. 
 This is a major source of false positives due to globals being declared in a
 header with some kind of incomplete (small) type, but the actual definition
 being bigger.

llvm-svn: 164912
---
 llvm/lib/Analysis/Lint.cpp | 18 +++++++++++-------
 llvm/test/Other/lint.ll    |  5 +++++
 2 files changed, 16 insertions(+), 7 deletions(-)

diff --git a/llvm/lib/Analysis/Lint.cpp b/llvm/lib/Analysis/Lint.cpp
index 9258aee..7bd9457 100644
--- a/llvm/lib/Analysis/Lint.cpp
+++ b/llvm/lib/Analysis/Lint.cpp
@@ -430,13 +430,17 @@ void Lint::visitMemoryReference(Instruction &I,
         BaseAlign = AI->getAlignment();
         if (BaseAlign == 0 && ATy->isSized())
           BaseAlign = TD->getABITypeAlignment(ATy);
-      } else if (GlobalValue *GV = dyn_cast<GlobalVariable>(Base)) {
-        Type *GTy = GV->getType()->getElementType();
-        if (GTy->isSized())
-          BaseSize = TD->getTypeAllocSize(GTy);
-        BaseAlign = GV->getAlignment();
-        if (BaseAlign == 0 && GTy->isSized())
-          BaseAlign = TD->getABITypeAlignment(GTy);
+      } else if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Base)) {
+        // If the global may be defined differently in another compilation unit
+        // then don't warn about funky memory accesses.
+        if (GV->hasDefinitiveInitializer()) {
+          Type *GTy = GV->getType()->getElementType();
+          if (GTy->isSized())
+            BaseSize = TD->getTypeAllocSize(GTy);
+          BaseAlign = GV->getAlignment();
+          if (BaseAlign == 0 && GTy->isSized())
+            BaseAlign = TD->getABITypeAlignment(GTy);
+        }
       }
 
       // Accesses from before the start or after the end of the object are not
diff --git a/llvm/test/Other/lint.ll b/llvm/test/Other/lint.ll
index d3ab988..78bbbe9 100644
--- a/llvm/test/Other/lint.ll
+++ b/llvm/test/Other/lint.ll
@@ -9,6 +9,7 @@ declare void @has_noaliases(i32* noalias %p, i32* %q)
 declare void @one_arg(i32)
 
 @CG = constant i32 7
+@E = external global i8
 
 define i32 @foo() noreturn {
   %buf = alloca i8
@@ -100,6 +101,10 @@ next:
   ret i32 0
 
 foo:
+; CHECK-NOT: Undefined behavior: Buffer overflow
+; CHECK-NOT: Memory reference address is misaligned
+  %e = bitcast i8* @E to i64*
+  store i64 0, i64* %e
   %z = add i32 0, 0
 ; CHECK: unreachable immediately preceded by instruction without side effects
   unreachable
-- 
2.7.4