| Message ID | 56309E44.8070100@arm.com |
|---|---|
| State | New |
| Headers | show |
On 28 October 2015 at 10:07, Kyrill Tkachov <kyrylo.tkachov@arm.com> wrote: > Hi all, > > This RTL checking error occurs on aarch64 in aarch_accumulator_forwarding > when processing an msubsi insn > with subregs: > (insn 15 14 16 3 (set (reg/v:SI 78 [ i ]) > (minus:SI (subreg:SI (reg/v:DI 76 [ aul ]) 0) > (mult:SI (subreg:SI (reg:DI 83) 0) > (subreg:SI (reg:DI 75 [ _20 ]) 0)))) schedice.c:10 357 > {*msubsi} > > The register_operand predicate for that pattern allows subregs (I think > correctly). > The code in aarch_accumulator_forwarding doesn't take that into account and > ends up > taking a REGNO of a SUBREG, causing a checking error. > > This patch fixes that by stripping the subregs off the accumulator rtx > before > checking that the inner expression is a REG and taking its REGNO. > > The testcase now works fine with an aarch64-none-elf toolchain configure for > RTL checking. > > The testcase is taken verbatim from the BZ entry for PR 68088. > Since this function is shared between arm and aarch64 I've bootstrapped and > tested it on both > and I'll need ok's for both ports. > > Ok for trunk? rtl.h exposes reg_or_subregno() already doesn't that do what we need here? The test case is not aarch64 specific therefore I think convention is that it should go into a generic directory. Cheers /Marcus
Hi Marcus, On 29/10/15 13:46, Marcus Shawcroft wrote: > On 28 October 2015 at 10:07, Kyrill Tkachov <kyrylo.tkachov@arm.com> wrote: >> Hi all, >> >> This RTL checking error occurs on aarch64 in aarch_accumulator_forwarding >> when processing an msubsi insn >> with subregs: >> (insn 15 14 16 3 (set (reg/v:SI 78 [ i ]) >> (minus:SI (subreg:SI (reg/v:DI 76 [ aul ]) 0) >> (mult:SI (subreg:SI (reg:DI 83) 0) >> (subreg:SI (reg:DI 75 [ _20 ]) 0)))) schedice.c:10 357 >> {*msubsi} >> >> The register_operand predicate for that pattern allows subregs (I think >> correctly). >> The code in aarch_accumulator_forwarding doesn't take that into account and >> ends up >> taking a REGNO of a SUBREG, causing a checking error. >> >> This patch fixes that by stripping the subregs off the accumulator rtx >> before >> checking that the inner expression is a REG and taking its REGNO. >> >> The testcase now works fine with an aarch64-none-elf toolchain configure for >> RTL checking. >> >> The testcase is taken verbatim from the BZ entry for PR 68088. >> Since this function is shared between arm and aarch64 I've bootstrapped and >> tested it on both >> and I'll need ok's for both ports. >> >> Ok for trunk? > rtl.h exposes reg_or_subregno() already doesn't that do what we need here? reg_or_subregno assumes that what it's passed is REG or a SUBREG. It will ICE on any other rtx. Here I want to strip the subreg if it is a subreg, but leave it as it is otherwise. > > The test case is not aarch64 specific therefore I think convention is > that it should go into a generic directory. Ok, I'll put it in gcc.dg/ Thanks, Kyrill > > Cheers > /Marcus >
On 29 October 2015 at 13:50, Kyrill Tkachov <kyrylo.tkachov@arm.com> wrote: >>> Ok for trunk? >> >> rtl.h exposes reg_or_subregno() already doesn't that do what we need here? > > > reg_or_subregno assumes that what it's passed is REG or a SUBREG. > It will ICE on any other rtx. Here I want to strip the subreg if it is > a subreg, but leave it as it is otherwise. OK, I follow. >> The test case is not aarch64 specific therefore I think convention is >> that it should go into a generic directory. > > > Ok, I'll put it in gcc.dg/ OK with the test case moved. Thanks /Marcus
On 06/11/15 17:07, Nikolai Bozhenov wrote: > On 11/06/2015 04:46 PM, Ramana Radhakrishnan wrote: >>> Hi! >>> >>> I faced the same issue but I had somewhat different RTL for the consumer: >>> >>> (insn 20 15 21 2 (set (reg/i:SI 0 r0) >>> (minus:SI (subreg:SI (reg:DI 117) 4) >>> (mult:SI (reg:SI 123) >>> (reg:SI 114)))) gasman.c:4 48 {*mulsi3subsi}) >>> >>> where (reg:DI 117) is produced by umulsidi3_v6 instruction. Is it >>> really true that (subreg:SI (reg:DI 117) 4) may be forwarded in one >>> cycle in this case? >> If the accumulator can be forwarded (i.e. a SImode register), there isn't a reason why a subreg:SI (reg:DI) will not get forwarded. >> >> The subreg:SI is an artifact before register allocation, thus it's a representation issue that the patch is fixing here unless I misunderstand your question. >> > I mean, in my example it is not the multiplication result that is > forwarded but its upper part. So, shouldn't we check that offset in a > subreg expression is zero? Or is it ok to forward only the upper part > of a multiplication? Could you please post the full RTL instruction we're talking about here as it appears in the scheduler dump? So that we're all on the same page about which case we're talking about. Thanks, Kyrill > > Thanks, > Nikolai >
On 06/11/15 17:09, Kyrill Tkachov wrote: > > On 06/11/15 17:07, Nikolai Bozhenov wrote: >> On 11/06/2015 04:46 PM, Ramana Radhakrishnan wrote: >>>> Hi! >>>> >>>> I faced the same issue but I had somewhat different RTL for the consumer: >>>> >>>> (insn 20 15 21 2 (set (reg/i:SI 0 r0) >>>> (minus:SI (subreg:SI (reg:DI 117) 4) >>>> (mult:SI (reg:SI 123) >>>> (reg:SI 114)))) gasman.c:4 48 {*mulsi3subsi}) >>>> >>>> where (reg:DI 117) is produced by umulsidi3_v6 instruction. Is it >>>> really true that (subreg:SI (reg:DI 117) 4) may be forwarded in one >>>> cycle in this case? >>> If the accumulator can be forwarded (i.e. a SImode register), there isn't a reason why a subreg:SI (reg:DI) will not get forwarded. >>> >>> The subreg:SI is an artifact before register allocation, thus it's a representation issue that the patch is fixing here unless I misunderstand your question. >>> >> I mean, in my example it is not the multiplication result that is >> forwarded but its upper part. So, shouldn't we check that offset in a >> subreg expression is zero? Or is it ok to forward only the upper part >> of a multiplication? > > Could you please post the full RTL instruction we're talking about here as it appears in the scheduler dump? > So that we're all on the same page about which case we're talking about. > Sorry, missed the above instruction. This subreg is just a pre-register allocation representation of the instruction and will go away after reload. This particular function only really has a real effect in post-reload scheduling as it's only there when the final register numbers are known. Kyrill > Thanks, > Kyrill > >> >> Thanks, >> Nikolai >> >
On 09/11/15 08:14, Nikolai Bozhenov wrote: > > > On 11/06/2015 08:16 PM, Kyrill Tkachov wrote: >> >> On 06/11/15 17:09, Kyrill Tkachov wrote: >>> >>> On 06/11/15 17:07, Nikolai Bozhenov wrote: >>>> On 11/06/2015 04:46 PM, Ramana Radhakrishnan wrote: >>>>>> Hi! >>>>>> >>>>>> I faced the same issue but I had somewhat different RTL for the consumer: >>>>>> >>>>>> (insn 20 15 21 2 (set (reg/i:SI 0 r0) >>>>>> (minus:SI (subreg:SI (reg:DI 117) 4) >>>>>> (mult:SI (reg:SI 123) >>>>>> (reg:SI 114)))) gasman.c:4 48 {*mulsi3subsi}) >>>>>> >>>>>> where (reg:DI 117) is produced by umulsidi3_v6 instruction. Is it >>>>>> really true that (subreg:SI (reg:DI 117) 4) may be forwarded in one >>>>>> cycle in this case? >>>>> If the accumulator can be forwarded (i.e. a SImode register), there isn't a reason why a subreg:SI (reg:DI) will not get forwarded. >>>>> >>>>> The subreg:SI is an artifact before register allocation, thus it's a representation issue that the patch is fixing here unless I misunderstand your question. >>>>> >>>> I mean, in my example it is not the multiplication result that is >>>> forwarded but its upper part. So, shouldn't we check that offset in a >>>> subreg expression is zero? Or is it ok to forward only the upper part >>>> of a multiplication? >>> >>> Could you please post the full RTL instruction we're talking about here as it appears in the scheduler dump? >>> So that we're all on the same page about which case we're talking about. >>> >> >> Sorry, missed the above instruction. >> This subreg is just a pre-register allocation representation of the instruction and will go away after reload. >> This particular function only really has a real effect in post-reload scheduling as it's only there when the final >> register numbers are known. >> > > I see. aarch_accumulator_forwarding always returns 0 for virtual > registers. But isn't it overly pessimistic to assume that accumulator > forwarding is never possible at sched1? I wonder if it would be better > to be more optimistic about register allocation outcome. I mean, in > case of virtual registers we could assume forwarding from A to B if B > is the only consumer of A's result. Something like this: > > if (REGNO (dest) >= FIRST_VIRTUAL_REGISTER > || REGNO (accumulator) >= FIRST_VIRTUAL_REGISTER) > return (DF_REG_USE_COUNT (REGNO (dest)) == 1) > && (DF_REF_INSN (DF_REG_USE_CHAIN (REGNO (dest))) == consumer); > else > return REGNO (dest) == REGNO (accumulator); > Interesting... As far as I know sched1 tries to minimise live ranges before register allocation rather than trying to perform the most exact pipeline modelling, since we only know the exact registers used in sched2. What you're proposing is a heuristic, so it would need benchmarking results and analysis to be considered. Thanks, Kyrill > Thanks, > Nikolai >
commit 7ce1b9ec8b8486cab34071a9c120db13e7c3b96a
Author: Kyrylo Tkachov <kyrylo.tkachov@arm.com>
Date: Tue Oct 27 11:42:19 2015 +0000
[ARM/AArch64] PR 68088: Fix RTL checking ICE due to subregs inside accumulator forwarding check
diff --git a/gcc/config/arm/aarch-common.c b/gcc/config/arm/aarch-common.c
index a940a02..2a21c4e 100644
--- a/gcc/config/arm/aarch-common.c
+++ b/gcc/config/arm/aarch-common.c
@@ -389,6 +389,15 @@ arm_mac_accumulator_is_result (rtx producer, rtx consumer)
&& !reg_overlap_mentioned_p (result, op1));
}
+/* If X is a subreg return the value it contains, otherwise
+ return X unchanged. */
+
+static rtx
+aarch_strip_subreg (rtx x)
+{
+ return GET_CODE (x) == SUBREG ? SUBREG_REG (x) : x;
+}
+
/* Return non-zero if the destination of PRODUCER feeds the accumulator
operand of an MLA-like operation. */
@@ -420,14 +429,14 @@ aarch_accumulator_forwarding (rtx_insn *producer, rtx_insn *consumer)
case PLUS:
/* Possibly an MADD. */
if (GET_CODE (XEXP (mla, 0)) == MULT)
- accumulator = XEXP (mla, 1);
+ accumulator = aarch_strip_subreg (XEXP (mla, 1));
else
return 0;
break;
case MINUS:
/* Possibly an MSUB. */
if (GET_CODE (XEXP (mla, 1)) == MULT)
- accumulator = XEXP (mla, 0);
+ accumulator = aarch_strip_subreg (XEXP (mla, 0));
else
return 0;
break;
@@ -441,7 +450,7 @@ aarch_accumulator_forwarding (rtx_insn *producer, rtx_insn *consumer)
{
/* FMADD/FMSUB. */
- accumulator = XEXP (mla, 2);
+ accumulator = aarch_strip_subreg (XEXP (mla, 2));
}
else if (REG_P (XEXP (mla, 1))
&& GET_CODE (XEXP (mla, 2)) == NEG
@@ -449,7 +458,7 @@ aarch_accumulator_forwarding (rtx_insn *producer, rtx_insn *consumer)
|| GET_CODE (XEXP (mla, 0)) == NEG))
{
/* FNMADD/FNMSUB. */
- accumulator = XEXP (XEXP (mla, 2), 0);
+ accumulator = aarch_strip_subreg (XEXP (XEXP (mla, 2), 0));
}
else
return 0;
@@ -460,6 +469,9 @@ aarch_accumulator_forwarding (rtx_insn *producer, rtx_insn *consumer)
return 0;
}
+ if (!REG_P (accumulator))
+ return 0;
+
return (REGNO (dest) == REGNO (accumulator));
}
diff --git a/gcc/testsuite/gcc.target/aarch64/pr68088_1.c b/gcc/testsuite/gcc.target/aarch64/pr68088_1.c
new file mode 100644
index 0000000..49c6aa1
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/pr68088_1.c
@@ -0,0 +1,15 @@
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+
+void bar (unsigned long);
+
+void
+foo (unsigned long aul, unsigned m, unsigned i)
+{
+ while (1)
+ {
+ aul += i;
+ i = aul % m;
+ bar (aul);
+ }
+}
Hi all, This RTL checking error occurs on aarch64 in aarch_accumulator_forwarding when processing an msubsi insn with subregs: (insn 15 14 16 3 (set (reg/v:SI 78 [ i ]) (minus:SI (subreg:SI (reg/v:DI 76 [ aul ]) 0) (mult:SI (subreg:SI (reg:DI 83) 0) (subreg:SI (reg:DI 75 [ _20 ]) 0)))) schedice.c:10 357 {*msubsi} The register_operand predicate for that pattern allows subregs (I think correctly). The code in aarch_accumulator_forwarding doesn't take that into account and ends up taking a REGNO of a SUBREG, causing a checking error. This patch fixes that by stripping the subregs off the accumulator rtx before checking that the inner expression is a REG and taking its REGNO. The testcase now works fine with an aarch64-none-elf toolchain configure for RTL checking. The testcase is taken verbatim from the BZ entry for PR 68088. Since this function is shared between arm and aarch64 I've bootstrapped and tested it on both and I'll need ok's for both ports. Ok for trunk? Thanks, Kyrill 2015-10-28 Kyrylo Tkachov <kyrylo.tkachov@arm.com> PR target/68088 * config/arm/aarch-common.c (aarch_strip_subreg): New function. (aarch_accumulator_forwarding): Strip subregs from accumulator rtx when appropriate. 2015-10-28 Kyrylo Tkachov <kyrylo.tkachov@arm.com> * gcc.target/aarch64/pr68088_1.c: New test.