On Fri, Dec 9, 2016 at 11:09 AM, Richard Biener
<richard.guent...@gmail.com> wrote:
> On Thu, Dec 8, 2016 at 10:44 PM, Uros Bizjak <ubiz...@gmail.com> wrote:
>> Hello!
>>
>> Attached patch fixes fall-out from excess-precision improvements
>> patch. As shown in the PR, the code throughout the compiler assumes
>> FLAG_PRECISION_FAST when flag_unsafe_math_optimizations flag is in
>> effect. The patch puts back two lines, removed by excess-precision
>> improvements patch.
>>
>> 2016-12-08 Uros Bizjak <ubiz...@gmail.com>
>>
>> PR middle-end/78738
>> * toplev.c (init_excess_precision): Initialize flag_excess_precision
>> to EXCESS_PRECISION_FAST for flag_unsafe_math_optimizations.
>>
>> testsuite/ChangeLog:
>>
>> 2016-12-08 Uros Bizjak <ubiz...@gmail.com>
>>
>> PR middle-end/78738
>> * gcc.target/i386/pr78738.c: New test.
>>
>> Patch was bootstrapped and regression tested on x86_64-linux-gnu {,-m32}.
>>
>> OK for mainline?
>
> Hmm, I think it belongs to set_unsafe_math_optimization_flags instead
> (and be consistent if -fexcess-precision was manually specified).
>
> Also where do we assume connection between -funsafe-math-optimizations
> and FLAG_PRECISION_FAST? We have two flags so we should fix any
> user that looks at one but means the other.
The failure is caused by the call to ix86_emit_i387_round in
"lround<X87MODEF:mode><SWI248x:mode>2" expander. This expander is
enabled for x87 math when flag_unsafe_math_optimizations is enabled.
In the called ix86_emit_i387_round, DFmode PLUS pattern is manually
emitted:
emit_insn (gen_rtx_SET (e2, gen_rtx_PLUS (inmode, e1, half)));
but due to the definition of X87_ENABLE_ARITH, DFmode fadd pattern
remains disabled.
It is possible to fix the failure by enabling X87_ENABLE_ARITH (and
X87_ENABLE_FLOAT) for flag_unsafe_math_optimizations (as is the case
in the attached v2 patch), but since gcc-6.x does
if (flag_unsafe_math_optimizations)
flag_excess_precision = EXCESS_PRECISION_FAST;
I though it was worth mentioning the difference between gcc-6 and
gcc-7. Probably, x87 is the only target that cares for it, in which
case the attached patch is sufficient.
Uros.
--cut here--
Index: i386.h
===================================================================
--- i386.h (revision 243523)
+++ i386.h (working copy)
@@ -693,13 +693,16 @@
/* 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)
+#define X87_ENABLE_ARITH(MODE) \
+ (flag_unsafe_math_optimizations \
+ || 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 \
+ (flag_unsafe_math_optimizations \
+ || flag_excess_precision == EXCESS_PRECISION_FAST \
|| (MODE) == XFmode \
|| ((MODE) == DFmode && (IMODE) == SImode) \
|| (IMODE) == HImode)
--cut here--
