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Re: [RFC PATCH, i386]: Enable post-reload compare elimination pass
On Sat, May 13, 2017 at 2:47 PM, Markus Trippelsdorf
<markus@trippelsdorf.de> wrote:
>> 2017-05-12 Uros Bizjak <ubizjak@gmail.com>
>>
>> * compare-elim.c (try_eliminate_compare): Canonicalize
>> operation with embedded compare to
>> [(set (reg:CCM) (compare:CCM (operation) (immediate)))
>> (set (reg) (operation)].
>>
>> * config/i386/i386.c (TARGET_FLAGS_REGNUM): New define.
>>
>> Re-bootstrapped and re-tested on x86_64-linux-gnu {,-m32}.
>>
>> Committed to mainline SVN.
>
> This causes gcc.dg/atomic/c11-atomic-exec-2.c to ICE with e.g.
> -march=nehalem:
>
> markus@x4 gcc % gcc -std=c11 -pedantic-errors -march=nehalem -O2 ./gcc/testsuite/gcc.dg/atomic/c11-atomic-exec-2.c
> ./gcc/testsuite/gcc.dg/atomic/c11-atomic-exec-2.c: In function ‘test_minus’:
> ./gcc/testsuite/gcc.dg/atomic/c11-atomic-exec-2.c:120:1: internal compiler error: in ix86_cc_mode, at config/i386/i386.c:22485
> }
> ^
> 0xea7b37 ix86_cc_mode(rtx_code, rtx_def*, rtx_def*)
> /home/markus/gcc/gcc/config/i386/i386.c:22485
> 0x1246e11 maybe_select_cc_mode
> /home/markus/gcc/gcc/compare-elim.c:500
> 0x1246e11 try_eliminate_compare
> /home/markus/gcc/gcc/compare-elim.c:665
> 0x1246e11 execute_compare_elim_after_reload
> /home/markus/gcc/gcc/compare-elim.c:727
> 0x1246e11 execute
> /home/markus/gcc/gcc/compare-elim.c:770
-mtune=intel is able to copy SFmode value through general registers,
resulting in the following sequence:
(insn 288 1008 1009 29 (parallel [
(set (reg:DI 4 si [687])
(lshiftrt:DI (reg:DI 4 si [687])
(const_int 32 [0x20])))
(clobber (reg:CC 17 flags))
]) "ttt.c":41 546 {*lshrdi3_1}
(nil))
(insn 1009 288 289 29 (set (reg:DI 2 cx [419])
(reg:DI 4 si [687])) "ttt.c":41 81 {*movdi_internal}
(nil))
(insn 289 1009 291 29 (set (reg:SF 21 xmm0 [425])
(reg:SF 2 cx [419])) "ttt.c":41 127 {*movsf_internal}
(nil))
(insn 291 289 292 29 (set (reg:CCFPU 17 flags)
(compare:CCFPU (reg:SF 21 xmm0 [425])
(reg:SF 27 xmm6 [688]))) "ttt.c":41 51 {*cmpiusf}
(expr_list:REG_EQUAL (compare:CCFPU (reg:SF 21 xmm0 [425])
(const_double:SF 0.0 [0x0.0p+0]))
(nil)))
Looking at compare-elim.c, equivalent_reg_at_start, the function
traces the value in %xmm0 to %rsi. So, try_eliminate_compare tries to
check if the target supports the compare of
(lshiftrt:DI (reg:DI 4 si [687])
(const_int 32 [0x20])))
with
(reg:SF 27 xmm6 [688])
which won't fly, since compare operands must have the same modes.
I'm testing the following patch that ensures that the mode of register
copy, found by equivalent_reg_at_start equals original mode.
--cut here--
Index: compare-elim.c
===================================================================
--- compare-elim.c (revision 247995)
+++ compare-elim.c (working copy)
@@ -526,6 +526,7 @@ maybe_select_cc_mode (struct comparison *cmp, rtx
static rtx
equivalent_reg_at_start (rtx reg, rtx_insn *end, rtx_insn *start)
{
+ machine_mode orig_mode = GET_MODE (reg);
rtx_insn *bb_head = BB_HEAD (BLOCK_FOR_INSN (end));
for (rtx_insn *insn = PREV_INSN (end);
@@ -572,6 +573,9 @@ equivalent_reg_at_start (rtx reg, rtx_insn *end, r
return NULL_RTX;
}
+ if (GET_MODE (reg) != orig_mode)
+ return NULL_RTX;
+
return reg;
}
--cut here--
Uros.