cvs commit: src/sys/amd64/include pcpu.h src/sys/i386/include pcpu.h
bde at FreeBSD.org
Tue Feb 6 16:21:11 UTC 2007
bde 2007-02-06 16:21:09 UTC
FreeBSD src repository
Simplified PCPU_GET() and PCPU_SET(). We must copy through a temporary
variable to avoid invalid constraints in dead code. Use an array of
u_char's (inside a struct) instead of a char/short/int/long variable so
that the variable and its accesses can be spelled in the same way in all
cases and code doesn't need to be cloned just to hold the spelling
Fixed strict-aliasing errors in PCPU_SET() and in the amd64 PCPU_GET().
Cast to (void *) as in rev.1.37 of the i386 version where the errors
were fixed for the i386 PCPU_GET() only. It would be more correct to
copy to and from the temp. variable using memcpy(), but then an
ifdef tangle would be required to ensure using the builtin memcpy().
We depend on fairly aggressive optimization to put the temp. variable
only in a register despite it being copied using
*(type *)(void *)&anothertype and could depend on this when using
memcpy() too. This seems to work right even for -O0, but the -O0 case
has not been completely tested.
This change gives identical object code for all object files in LINT
on amd64 (except for one file with a __TIME__ stamp). For LINT on
i386 it gives unimportant differences in instruction order and padding
in a few object files. This was only tested for -O.
This change (actually a previous version of it) gives the following
reductions in the number of object files in LINT that fail to compile
with -O2 but without the -fno-strict-aliasing kludge:
- amd64: 29 (down from 211)
- i386: 36 (down from 47)
gcc-3.4.6 actually allows the invalid constraints that result from not
using the temp. variable, at least with -O[1-2], but gcc-3.3.3 crashes
on them and I don't want to depend on compiler bugs.
Revision Changes Path
1.45 +18 -48 src/sys/amd64/include/pcpu.h
1.47 +18 -36 src/sys/i386/include/pcpu.h
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