From 51b84d796c62fbb2a31e990310a4cba61e46b87a Mon Sep 17 00:00:00 2001
From: Kostya Serebryany <kcc@google.com>
Date: Mon, 18 Mar 2013 09:38:39 +0000
Subject: [PATCH] [asan] when creating string constants, set unnamed_attr and
align 1 so that equal strings are merged by the linker. Observed up to 1%
binary size reduction. Thanks to Anton Korobeynikov for the suggestion
llvm-svn: 177264
---
lib/Transforms/Instrumentation/AddressSanitizer.cpp | 5 ++++-
.../AddressSanitizer/do-not-instrument-internal-globals.ll | 5 +++--
2 files changed, 7 insertions(+), 3 deletions(-)
diff --git a/lib/Transforms/Instrumentation/AddressSanitizer.cpp b/lib/Transforms/Instrumentation/AddressSanitizer.cpp
index 614dc210a03..92b42ee64b0 100644
--- a/lib/Transforms/Instrumentation/AddressSanitizer.cpp
+++ b/lib/Transforms/Instrumentation/AddressSanitizer.cpp
@@ -531,9 +531,12 @@ static size_t TypeSizeToSizeIndex(uint32_t TypeSize) {
// Create a constant for Str so that we can pass it to the run-time lib.
static GlobalVariable *createPrivateGlobalForString(Module &M, StringRef Str) {
Constant *StrConst = ConstantDataArray::getString(M.getContext(), Str);
- return new GlobalVariable(M, StrConst->getType(), true,
+ GlobalVariable *GV = new GlobalVariable(M, StrConst->getType(), true,
GlobalValue::PrivateLinkage, StrConst,
kAsanGenPrefix);
+ GV->setUnnamedAddr(true); // Ok to merge these.
+ GV->setAlignment(1); // Strings may not be merged w/o setting align 1.
+ return GV;
}
static bool GlobalWasGeneratedByAsan(GlobalVariable *G) {
diff --git a/test/Instrumentation/AddressSanitizer/do-not-instrument-internal-globals.ll b/test/Instrumentation/AddressSanitizer/do-not-instrument-internal-globals.ll
index 2efd6b1e0d1..0928c494154 100644
--- a/test/Instrumentation/AddressSanitizer/do-not-instrument-internal-globals.ll
+++ b/test/Instrumentation/AddressSanitizer/do-not-instrument-internal-globals.ll
@@ -14,6 +14,7 @@ entry:
declare void @_Z3fooPi(i32*)
; We create one global string constant for the stack frame above.
+; It should have unnamed_addr and align 1.
; Make sure we don't create any other global constants.
-; CHECK: = private constant
-; CHECK-NOT: = private constant
+; CHECK: = private unnamed_addr constant{{.*}}align 1
+; CHECK-NOT: = private unnamed_addr constant