[libcxx-commits] [libcxx] c68a9d2 - [ASan][libc++] String annotations optimizations fix with lambda (#76200)

[via libcxx-commits]

Author: Tacet
Date: 2024-01-08T18:02:17+01:00
New Revision: c68a9d25e99a096f6862fc4b57dd380a21245d31

URL: https://github.com/llvm/llvm-project/commit/c68a9d25e99a096f6862fc4b57dd380a21245d31
DIFF: https://github.com/llvm/llvm-project/commit/c68a9d25e99a096f6862fc4b57dd380a21245d31.diff

LOG: [ASan][libc++] String annotations optimizations fix with lambda (#76200)

This commit addresses optimization and instrumentation challenges
encountered within comma constructors.
1) _LIBCPP_STRING_INTERNAL_MEMORY_ACCESS does not work in comma
constructors.
2) Code inside comma constructors is not always correctly optimized.
Problematic code examples:
- `: __r_(((__str.__is_long() ? 0 : (__str.__annotate_delete(), 0)),
std::move(__str.__r_))) {`
- `: __r_(__r_([&](){ if(!__s.__is_long()) __s.__annotate_delete();
return std::move(__s.__r_);}())) {`

However, lambda with argument seems to be correctly optimized. The patch employs this.

Use of lambda based on an idea from @ldionne.

Added: 
    

Modified: 
    libcxx/include/string

Removed: 
    


################################################################################
diff  --git a/libcxx/include/string b/libcxx/include/string
index c676182fba8bac..e2be53eaee2417 100644
--- a/libcxx/include/string
+++ b/libcxx/include/string
@@ -922,7 +922,7 @@ public:
       // Turning off ASan instrumentation for variable initialization with _LIBCPP_STRING_INTERNAL_MEMORY_ACCESS
       // does not work consistently during initialization of __r_, so we instead unpoison __str's memory manually first.
       // __str's memory needs to be unpoisoned only in the case where it's a short string.
-      : __r_(((__str.__is_long() ? 0 : (__str.__annotate_delete(), 0)), std::move(__str.__r_))) {
+      : __r_([](basic_string &__s){ if(!__s.__is_long()) __s.__annotate_delete(); return std::move(__s.__r_); }(__str)) {
     __str.__r_.first() = __rep();
     __str.__annotate_new(0);
     if (!__is_long())