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Re: [PATCH] support to flip modes in sh mode-switching
- From: Uros Bizjak <ubizjak at gmail dot com>
- To: GCC Patches <gcc-patches at gcc dot gnu dot org>
- Cc: Christian BRUEL <christian dot bruel at st dot com>, amylaar at gcc dot gnu dot org
- Date: Fri, 22 Dec 2006 19:15:28 +0100
- Subject: Re: [PATCH] support to flip modes in sh mode-switching
This optimization is useful for the sh4-300. I don't know any other
architecture supported by gcc to test it. It also shares the same
module than the i386 targets to support mode switching.
I know one ;)
Looking briefly at your patch, it seems to me that it also implements
the infrastructure needed for reliable x87<->MMX mode switching. As
described in PR target/19161 (comment #16 and #17), the patch that used
mode switching, failed for certain CFGs. For certain CFG layouts, it was
possible to enter a BB with both (MMX and X87) modes active. The patch
was designed to ICE for this situation, as both register sets were
disabled in this case. However, having mode _flipping_ patch, this
situation can be resolved.
Bootstrapped the compiler and tested for no regression on
i686-pc-linux-gnu check-gcc. If there are specific flags to stress 387
modes I would be happy to run more tests.
You could create some loops and branches, where floor(), ceil() and
perhaps trunc() functions are used. Try to compile it with -O2
-ffast-math and this should exercise x87 mode switching stuff.
And BTW (looking at PR 28764, comment #12 by Jorn): x87 does not insert
mode _switching_ code, but inserts code where mode control words are
calculated. The reason that separate entities are used is due to
"combining" of code that sets control bits. We can calculate a couple of
control words at _one_ insertion point and use these words in actual
double test(double *a, int x)
double z = 0.0;
for (i = 0; i < x; i++)
z += floor(a[i]) + ceil(a[i]);
Compile this with -O2 -ffast-math to see that only ONE fstcw is used.
Don't bother with fldcw insns...
IMO "* config/sh/sh.h" in the last line.
* basic-block.h (pre_edge_lcm_avs): Declare
* config/i386/i386.h (EMIT_MODE_SET): Add ACTUALMODE parameter.
* doc/tm.texi (EMIT_MODE_SET): Idem.
* config/i386/sh.h (EMIT_MODE_SET): Idem. Call emit_fpu_flip.