[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

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@177264 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 7 insertions, 3 deletions

diff --git a/lib/Transforms/Instrumentation/AddressSanitizer.cpp b/lib/Transforms/Instrumentation/AddressSanitizer.cpp
index 614dc21..92b42ee 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 2efd6b1..0928c49 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