Hi,
Michael Cree wrote:
> On 15/07/2012, at 8:50 AM, Jonathan Nieder wrote:
>> gcc takes full advantage by converting the get_be32
>> calls back to a load and bswap and producing a whole bunch of
>> unaligned access traps.
>
> Alpha does not have a bswap (or similar) instruction.
[...]
> . If the pointer is unaligned
> then two neighbouring aligned 32bit loads are required to ensure
> that all four bytes are loaded. If the pointer is aligned then a
> single 32bit load gets all the four bytes. Having never looked at
> the generated assembler code, I nevertheless suspect that is the
> guts of the optimisation --- the compiler can eliminate an access to
> memory if it knows the pointer is aligned.
How about:
gcc takes full advantage by using a single 32-bit load,
resulting in a whole bunch of unaligned access traps.
You can see the generated assembler with "make block-sha1/sha1.s" and
reading the resulting sha1.s file in the current working directory
(oops). I don't have an alpha cross-compiler installed or access to
an alpha to check for myself.
-- >8 --
Subject: Makefile: fix location of listing produced by "make subdir/foo.s"
When I invoke "make block-sha1/sha1.s", 'make' runs $(CC) -S without
specifying where it should put its output and the output ends up in
./sha1.s. Confusing.
Add an -o option to the .s rule to fix this. We were already doing
that for most compiler invocations but had forgotten it for the
assembler listings.
Signed-off-by: Jonathan Nieder <[email protected]>
---
Thanks,
Jonathan
Makefile | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/Makefile b/Makefile
index dc709029..e8d2798f 100644
--- a/Makefile
+++ b/Makefile
@@ -2230,7 +2230,7 @@ $(ASM_OBJ): %.o: %.S GIT-CFLAGS $(missing_dep_dirs)
endif
%.s: %.c GIT-CFLAGS FORCE
- $(QUIET_CC)$(CC) -S $(ALL_CFLAGS) $(EXTRA_CPPFLAGS) $<
+ $(QUIET_CC)$(CC) -o $@ -S $(ALL_CFLAGS) $(EXTRA_CPPFLAGS) $<
ifdef USE_COMPUTED_HEADER_DEPENDENCIES
# Take advantage of gcc's on-the-fly dependency generation
--
1.7.10.4
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