https://bugs.llvm.org/show_bug.cgi?id=43710
Bug ID: 43710
Summary: clang++ miscompiles against MSVC standard library with
-O2
Product: new-bugs
Version: 9.0
Hardware: PC
OS: other
Status: NEW
Severity: normal
Priority: P
Component: new bugs
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected], [email protected]
Created attachment 22688
--> https://bugs.llvm.org/attachment.cgi?id=22688&action=edit
Test program
Hello,
My system is Windows 10 with clang 9.0.0 (installed with
https://releases.llvm.org/9.0.0/LLVM-9.0.0-win64.exe) and Microsoft Visual
Studio Community 2019, Version 16.3.1.
Under some circumstances a non-empty string passed into a function is seen by
the function code as an empty string.
The attached program reproduces the issue. It is expected to print 'abc' but
prints '' if compiled with -O2 or -O3:
> clang++ -std=c++2a test.cxx
> a.exe
'abc'
>clang++ -std=c++2a -O2 test.cxx
>a.exe
''
Note that the issue also reproduces if compile with clang-cl:
> clang-cl /std:c++17 /EHsc test.cxx
> test.exe
'abc'
> clang-cl /std:c++17 /EHsc /O2 test.cxx
> test.exe
''
Also note that the attached program is not exactly trivial but I was unable to
reduce it further.
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