https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78738
Uroš Bizjak <ubizjak at gmail dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Last reconfirmed| |2016-12-08
CC| |jgreenhalgh at gcc dot gnu.org
Ever confirmed|0 |1
--- Comment #2 from Uroš Bizjak <ubizjak at gmail dot com> ---
Looks like the effect of excess_precision changes.
In i386.h, we define:
/* Whether to allow x87 floating-point arithmetic on MODE (one of
SFmode, DFmode and XFmode) in the current excess precision
configuration. */
#define X87_ENABLE_ARITH(MODE) \
(flag_excess_precision == EXCESS_PRECISION_FAST || (MODE) == XFmode)
/* Likewise, whether to allow direct conversions from integer mode
IMODE (HImode, SImode or DImode) to MODE. */
#define X87_ENABLE_FLOAT(MODE, IMODE) \
(flag_excess_precision == EXCESS_PRECISION_FAST \
|| (MODE) == XFmode \
|| ((MODE) == DFmode && (IMODE) == SImode) \
|| (IMODE) == HImode)
and relevant pattern in i386.md:
(define_insn "*fop_<mode>_comm"
[(set (match_operand:MODEF 0 "register_operand" "=f,x,v")
(match_operator:MODEF 3 "binary_fp_operator"
[(match_operand:MODEF 1 "nonimmediate_operand" "%0,0,v")
(match_operand:MODEF 2 "nonimmediate_operand" "fm,xm,vm")]))]
"((SSE_FLOAT_MODE_P (<MODE>mode) && TARGET_SSE_MATH)
|| (TARGET_80387 && X87_ENABLE_ARITH (<MODE>mode)))
&& COMMUTATIVE_ARITH_P (operands[3])
&& !(MEM_P (operands[1]) && MEM_P (operands[2]))"
The testcase generates the insn from ix86_emit_i387_round, where
flag_excess_precision is set to EXCESS_PRECISION_STANDARD.
IMO, we want to set flag_excess_precision to EXCESS_PRECISION_FAST for
-ffast-math.
Confirmed, CC author of the patch.
