https://bugs.kde.org/show_bug.cgi?id=442168
Bug ID: 442168
Summary: Floating-point erroneous behavior with memecheck with
regards to class (isfinite(), etc.)
Product: valgrind
Version: 3.15 SVN
Platform: Other
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: memcheck
Assignee: jsew...@acm.org
Reporter: xavier.ro...@algolia.com
Target Milestone: ---
Created attachment 141383
--> https://bugs.kde.org/attachment.cgi?id=141383&action=edit
Minimal program demonstrating floating-point erroneous behavior with memcheck
SUMMARY
Floating-point erroneous behavior with memecheck with regards to class
(isfinite(), etc.), leading to consider -NaN as a finite number.
STEPS TO REPRODUCE
1. Compile the attached reproducible minimal case with clang-12 in at least O2
and -march=corei7-avx
clang-12 -std=c++20 -stdlib=libc++ -O2 -march=corei7-avx
isfinite-bug-with-clang12-O2-corei7-avx.cpp -lc++ -lm -o isfinite-bug
2. Run without valgrind
./isfinite-bug
3. Run with valgrind (valgrind --tool=memcheck)
valgrind --tool=memcheck ./isfinite-bug
OBSERVED RESULT
Run without valgrind: "All right" is emitted
Run with valgrind: "Error: expected 1 and got -nan" is emitted
EXPECTED RESULT
The valgrind version should always emit "All right"
SOFTWARE/OS VERSIONS
Linux, Ubuntu, 5.4.0-80-generic
ADDITIONAL INFORMATION
The issue is reproduced using valgrind-3.15.0
It requires:
* clang-12
* At least O2
* -march=corei7-avx
It is _not_ reproduced with an earlier version of clang (tested version:
clang-11), which hints of a recent special NaN/fp class optimization.
At this stage, I can not guarantee that this is a valgrind issue, or a
undefined-behavior-generated-code that happen to work without valgrind.
I'm available for any additional information.
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