MS ABI: Eliminate Duplicate Strings

COFF doesn't have mergeable sections so LLVM/clang's normal tactics for
string deduplication will not have any effect.

To remedy this we place each string inside it's own section and mark
the section as IMAGE_COMDAT_SELECT_ANY.  However, we can only do this if the
string has an external name that we can generate from it's contents.

To be compatible with MSVC, we must use their scheme.  Otherwise identical
strings in translation units from clang may not be deduplicated with
translation units in MSVC.

This fixes PR18248.

N.B. We will not attempt to do anything with a string literal which is not of
type 'char' or 'wchar_t' because their compiler does not support unicode
string literals as of this date.  Further, we avoid doing this if
either -fwritable-strings or -fsanitize=address are present.

This reverts commit r204596.

llvm-svn: 204675

1 files changed, 6 insertions, 3 deletions

diff --git a/clang/test/CodeGen/string-literal-short-wstring.c b/clang/test/CodeGen/string-literal-short-wstring.c
index 88e4a1e4008..89aa6f76ca4 100644
--- a/clang/test/CodeGen/string-literal-short-wstring.c
+++ b/clang/test/CodeGen/string-literal-short-wstring.c
@@ -1,4 +1,5 @@
-// RUN: %clang_cc1 -x c++ -emit-llvm -fshort-wchar %s -o - | FileCheck %s
+// RUN: %clang_cc1 -x c++ -triple %itanium_abi_triple -emit-llvm -fshort-wchar %s -o - | FileCheck %s --check-prefix=CHECK --check-prefix=ITANIUM
+// RUN: %clang_cc1 -x c++ -triple %ms_abi_triple -emit-llvm -fshort-wchar %s -o - | FileCheck %s --check-prefix=CHECK --check-prefix=MSABI
 // Runs in c++ mode so that wchar_t is available.
 
 int main() {
@@ -6,11 +7,13 @@ int main() {
   // CHECK: private unnamed_addr constant [10 x i8] c"\E1\84\A0\C8\A0\F4\82\80\B0\00", align 1
   char b[10] = "\u1120\u0220\U00102030";
 
-  // CHECK: private unnamed_addr constant [3 x i16] [i16 65, i16 66, i16 0]
+  // ITANIUM: private unnamed_addr constant [3 x i16] [i16 65, i16 66, i16 0]
+  // MSABI: linkonce_odr unnamed_addr constant [3 x i16] [i16 65, i16 66, i16 0]
   const wchar_t *foo = L"AB";
 
   // This should convert to utf16.
-  // CHECK: private unnamed_addr constant [5 x i16] [i16 4384, i16 544, i16 -9272, i16 -9168, i16 0]
+  // ITANIUM: private unnamed_addr constant [5 x i16] [i16 4384, i16 544, i16 -9272, i16 -9168, i16 0]
+  // MSABI: linkonce_odr unnamed_addr constant [5 x i16] [i16 4384, i16 544, i16 -9272, i16 -9168, i16 0]
   const wchar_t *bar = L"\u1120\u0220\U00102030";