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Re: [PATCH, ARM] Fix ABI for double-precision helpers on single-float-only CPUs


On Thu, 02 Jun 2011 16:35:01 +0100
Richard Earnshaw <rearnsha@arm.com> wrote:

> I see Paul has already approved this, but I've just spotted one
> potential problem that might cause latent bugs sometime in the future.
> 
> The code to register the libcalls is only run once, the first time we
> try to look up a libcall.  If we ever end up allowing dynamic changing
> of CPU and optimization options, not registering the other libcalls
> will lead to subtle problems at run time.  I suggest that these
> functions be unconditionally added along with the other libcalls.

Done.

> I also don't understand why all the tests are needed in
> arm_init_cumulative_args?  Surely arm_libcall_uses_aapcs_base() will
> already have run that test.

I did some archaeology to try to figure out why things were like that
(the patch was written a while ago) -- and yeah, it looks like it's
completely unnecessary to have those tests in arm_init_cumulative_args.
That bit of code was refactored a while ago, and it looks like the
patch wasn't ever updated properly. My mistake!

I'm re-testing the attached version.

Thanks,

Julian

ChangeLog

    gcc/
    * config/arm/arm.c (arm_libcall_uses_aapcs_base): Use correct ABI
    for double-precision helper functions in hard-float mode if only
    single-precision arithmetic is supported in hardware.
commit 8084eeee248e648e3276b91a957f667c299f84e1
Author: Julian Brown <julian@henry7.codesourcery.com>
Date:   Fri Jun 3 04:34:23 2011 -0700

    VFP ABI fix for double-precision helpers on single-only processors.

diff --git a/gcc/config/arm/arm.c b/gcc/config/arm/arm.c
index 057f9ba..a1d009b 100644
--- a/gcc/config/arm/arm.c
+++ b/gcc/config/arm/arm.c
@@ -3345,6 +3345,28 @@ arm_libcall_uses_aapcs_base (const_rtx libcall)
 		   convert_optab_libfunc (sfix_optab, DImode, SFmode));
       add_libcall (libcall_htab,
 		   convert_optab_libfunc (ufix_optab, DImode, SFmode));
+
+      /* Values from double-precision helper functions are returned in core
+	 registers if the selected core only supports single-precision
+	 arithmetic, even if we are using the hard-float ABI.  The same is
+	 true for single-precision helpers, but we will never be using the
+	 hard-float ABI on a CPU which doesn't support single-precision
+	 operations in hardware.  */
+      add_libcall (libcall_htab, optab_libfunc (add_optab, DFmode));
+      add_libcall (libcall_htab, optab_libfunc (sdiv_optab, DFmode));
+      add_libcall (libcall_htab, optab_libfunc (smul_optab, DFmode));
+      add_libcall (libcall_htab, optab_libfunc (neg_optab, DFmode));
+      add_libcall (libcall_htab, optab_libfunc (sub_optab, DFmode));
+      add_libcall (libcall_htab, optab_libfunc (eq_optab, DFmode));
+      add_libcall (libcall_htab, optab_libfunc (lt_optab, DFmode));
+      add_libcall (libcall_htab, optab_libfunc (le_optab, DFmode));
+      add_libcall (libcall_htab, optab_libfunc (ge_optab, DFmode));
+      add_libcall (libcall_htab, optab_libfunc (gt_optab, DFmode));
+      add_libcall (libcall_htab, optab_libfunc (unord_optab, DFmode));
+      add_libcall (libcall_htab, convert_optab_libfunc (sext_optab, DFmode,
+							SFmode));
+      add_libcall (libcall_htab, convert_optab_libfunc (trunc_optab, SFmode,
+							DFmode));
     }
 
   return libcall && htab_find (libcall_htab, libcall) != NULL;

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