[PATCH] Aarch64: Define WIDEST_HARDWARE_FP_SIZE

[Eric Botcazou]

Hi,

the macro is documented like this in the internal manual:

 -- Macro: WIDEST_HARDWARE_FP_SIZE
     A C expression for the size in bits of the widest floating-point
     format supported by the hardware.  If you define this macro, you
     must specify a value less than or equal to mode precision of the
     mode used for C type 'long double' (from hook
     'targetm.c.mode_for_floating_type' with argument
     'TI_LONG_DOUBLE_TYPE').  If you do not define this macro, mode
     precision of the mode used for C type 'long double' is the default.

AArch64 uses 128-bit TFmode for long double but, as far as I know, no FPU 
implemented in hardware supports it.

WIDEST_HARDWARE_FP_SIZE is taken into account in exactly two places:
  - in libgcc for the implementation of float[uns]ti{sd}f,
  - in the Ada front-end to cap the size clauses of floating-point types.

The effect of the change on the first place can be seen by running nm on 
libgcc/_floatdisf.o (which implements floattisf for Aarch64), from:
                 U __addtf3
                 U __floatditf
0000000000000000 T __floattisf
                 U __floatunditf
                 U __multf3
                 U __trunctfsf2
to just
0000000000000000 T __floattisf

The effect of the change on the second place can be seen on the attached Ada 
testcase, which fails without it and passes with it.

Bootstrapped/regtested on Aarch64/Linux, OK for the mainline?


2024-10-01  Eric Botcazou  <ebotca...@adacore.com>

        * config/aarch64/aarch64.h (WIDEST_HARDWARE_FP_SIZE): Define to 64.


2024-10-01  Eric Botcazou  <ebotca...@adacore.com>

        * gnat.dg/specs/size_clause6.ads: New test.

-- 
Eric Botcazou
diff --git a/gcc/config/aarch64/aarch64.h b/gcc/config/aarch64/aarch64.h
index ec8fde783b3..acc26aed808 100644
--- a/gcc/config/aarch64/aarch64.h
+++ b/gcc/config/aarch64/aarch64.h
@@ -96,6 +96,8 @@
 
 #define LONG_LONG_TYPE_SIZE	64
 
+#define WIDEST_HARDWARE_FP_SIZE	64
+
 /* This value is the amount of bytes a caller is allowed to drop the stack
    before probing has to be done for stack clash protection.  */
 #define STACK_CLASH_CALLER_GUARD 1024

-- { dg-do compile }

with Interfaces;

package Size_Clause6 is

  type Long_Double is new Interfaces.IEEE_Extended_Float;
  for Long_Double'Size use 128; -- { dg-warning "unused" "" { target { ! { { i?86-*-* x86_64-*-* } && lp64 } } } }

  function Int (X : in Long_Double) return Integer is (0);

end Size_Clause6;