https://bugs.kde.org/show_bug.cgi?id=371989
Bug ID: 371989
Summary: PCMPISTRM $0x72 validity bit propagation is imprecise
Product: valgrind
Version: 3.12 SVN
Platform: Compiled Sources
OS: Linux
Status: UNCONFIRMED
Severity: normal
Priority: NOR
Component: memcheck
Assignee: jsew...@acm.org
Reporter: lopre...@gmail.com
Target Milestone: ---
Created attachment 101977
--> https://bugs.kde.org/attachment.cgi?id=101977&action=edit
Test case illustrating pcmpistrm $0x72 validity bit propagation failure
(cf. bug 309921)
Well, here we go again...
The attached program uses inline assembly to do something similar to the Intel
C compiler's optimized "strspn()" routine.
It would be easy for me to use a suppression rule for warnings from inside the
routine. But as with this example, memcheck generates a warning *outside* of
the vectorized function.
So, memcheck is tainting the return value of the function as undefined. But the
result is actually perfectly well-defined thanks to (a) the memory alignment of
the arguments and (b) the way PCMPISTRM ignores everything after the first null
byte.
--
You are receiving this mail because:
You are watching all bug changes.
