[Bug target/70465] [5/6 Regression] Poor code for x87 asm

[ubizjak at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70465

Uroš Bizjak <ubizjak at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |REOPENED
         Resolution|FIXED                       |---

--- Comment #16 from Uroš Bizjak <ubizjak at gmail dot com> ---
Looking at some other PR, I have noticed that following testcase:

--cut here--
extern float global_data[1024];

static long double MIN (long double a, long double b) { return a < b ? a : b; }
static long double MAX (long double a, long double b) { return a > b ? a : b; }

float bar (void)
{
  long double delta = (global_data[0]);

  return (MIN (MAX (delta, 0.0l), 1.0l));
}
--cut here--

compiles with -Ofast -mfpmath=387 to:

bar:
        flds    global_data(%rip)
        fldz
        fxch    %st(1)

The above shows that we can also consider x87 constants and float-extend from
memory when avoiding fxchs:

__.297r.stack:

(insn:TI 6 13 37 2 (set (reg:XF 8 st)
        (float_extend:XF (mem/c:SF (symbol_ref:DI ("global_data") [flags 0x40] 
<var_decl 0x2ac721f3ae10 global_data>) [1 global_data+0 S4 A32])))
"pr79593.c":12 153 {*extendsfxf2_i387}
     (nil))
(insn:TI 37 6 46 2 (set (reg:XF 8 st)
        (const_double:XF 0.0 [0x0.0p+0])) "pr79593.c":8 123 {*movxf_internal}
     (expr_list:REG_EQUAL (const_double:XF 0.0 [0x0.0p+0])
        (nil)))
(insn 46 37 11 2 (parallel [
            (set (reg:XF 9 st(1))
                (reg:XF 8 st))
            (set (reg:XF 8 st)
                (reg:XF 9 st(1)))
        ]) "pr79593.c":8 -1
     (nil))