[llvm] r177264 - [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

[Kostya Serebryany]

Author: kcc
Date: Mon Mar 18 04:38:39 2013
New Revision: 177264

URL: http://llvm.org/viewvc/llvm-project?rev=177264&view=rev
Log:
[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

Modified:
    llvm/trunk/lib/Transforms/Instrumentation/AddressSanitizer.cpp
    llvm/trunk/test/Instrumentation/AddressSanitizer/do-not-instrument-internal-globals.ll

Modified: llvm/trunk/lib/Transforms/Instrumentation/AddressSanitizer.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Instrumentation/AddressSanitizer.cpp?rev=177264&r1=177263&r2=177264&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Instrumentation/AddressSanitizer.cpp (original)
+++ llvm/trunk/lib/Transforms/Instrumentation/AddressSanitizer.cpp Mon Mar 18 04:38:39 2013
@@ -531,9 +531,12 @@ static size_t TypeSizeToSizeIndex(uint32
 // 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) {

Modified: llvm/trunk/test/Instrumentation/AddressSanitizer/do-not-instrument-internal-globals.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Instrumentation/AddressSanitizer/do-not-instrument-internal-globals.ll?rev=177264&r1=177263&r2=177264&view=diff
==============================================================================
--- llvm/trunk/test/Instrumentation/AddressSanitizer/do-not-instrument-internal-globals.ll (original)
+++ llvm/trunk/test/Instrumentation/AddressSanitizer/do-not-instrument-internal-globals.ll Mon Mar 18 04:38:39 2013
@@ -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