https://bugs.kde.org/show_bug.cgi?id=493970
Bug ID: 493970
Summary: s390x: Store/restore FPC upon helper call causes
slowdown
Classification: Developer tools
Product: valgrind
Version: unspecified
Platform: Other
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: vex
Assignee: jsew...@acm.org
Reporter: ar...@linux.ibm.com
Target Milestone: ---
Currently the host's floating-point control register FPC is stored before
calling a helper function and restored afterwards. This causes a measurable
slowdown when using helper-heavy tools like memcheck.
The host FPC seems to be used only for setting the rounding mode before
performing a floating-point operation. This is typically done once per SB.
I'm not aware of a helper function that changes the rounding mode. Such a
behavior would only be acceptable if the helper was explicitly meant to do
this, e.g., if it somehow participated in implementing the rounding-mode
behavior. If so, keeping the updated FPC value would obviously be preferable.
The same applies to the other FPC bits; if they were used and a helper changed
them, keeping the updated values would probably be a more useful general
approach.
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