[Bug tree-optimization/103298] New: [12 regressions] regressions on arm after r12-5301

[Bug tree-optimization/103298] New: [12 regressions] regressions on arm after r12-5301

[clyon at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103298

            Bug ID: 103298
           Summary: [12 regressions] regressions on arm after r12-5301
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: clyon at gcc dot gnu.org
  Target Milestone: ---

r12-5301 is causing regressions on some arm targets:

arm-none-linux-gnueabi -march=armv7-a -mthumb:
FAIL: gcc.target/arm/pr42093.c scan-assembler-not tbb
FAIL: gcc.target/arm/pr43920-2.c object-size text <= 54

arm-none-linux-gnueabi -march=armv5t -mthumb:
FAIL: gcc.dg/tree-ssa/if-to-switch-3.c scan-tree-dump iftoswitch "Condition
chain with [^\n\r]* BBs transformed into a switch statement."

[Bug tree-optimization/103298] [12 regressions] regressions on arm after r12-5301

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103298

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Christophe Lyon from comment #0) 
> arm-none-linux-gnueabi -march=armv5t -mthumb:
> FAIL: gcc.dg/tree-ssa/if-to-switch-3.c scan-tree-dump iftoswitch "Condition
> chain with [^\n\r]* BBs transformed into a switch statement."

PR 103278.

[Bug tree-optimization/103298] [12 regressions] regressions on arm after r12-5301

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103298

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |12.0
           Keywords|                            |missed-optimization

[Bug tree-optimization/103298] [12 regressions] regressions on arm after r12-5301

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103298

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|unassigned at gcc dot gnu.org      |rguenth at gcc dot gnu.org
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2021-11-18

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
I will have a look.

[Bug testsuite/103298] [12 regressions] regressions on arm after r12-5301

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103298

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|rguenth at gcc dot gnu.org         |unassigned at gcc dot gnu.org
                 CC|                            |ramana at gcc dot gnu.org,
                   |                            |rguenth at gcc dot gnu.org
             Status|ASSIGNED                    |NEW
          Component|tree-optimization           |testsuite

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Christophe Lyon from comment #0)
> r12-5301 is causing regressions on some arm targets:
> 
> arm-none-linux-gnueabi -march=armv7-a -mthumb:
> FAIL: gcc.target/arm/pr42093.c scan-assembler-not tbb

The testcase seems to be for a wrong-code issue but was implemented as
scan-assembler one which is now seemingly dependent on switch expansion
heuristics.

Previously we got

        ldr     pc, [r6, r2, lsl #2]
        .align  2
.L6:
        .word   .L14+1
...

but now

        cmp     r2, #50
        bhi     .L1
        tbb     [pc, r2]
.L5:
        .byte   (.L7-.L5)/2
...

which  looks more optimal to me.  So the testcase is simply bogus?  Defering
to ARM folks.


> FAIL: gcc.target/arm/pr43920-2.c object-size text <= 54

--- a/pr43920-2.s       2021-11-18 10:32:22.975744703 +0100
+++ b/pr43920-2.s       2021-11-18 10:31:56.763399263 +0100
@@ -34,18 +34,19 @@
        mov     r0, r7
        bl      lseek
        adds    r2, r4, #1
-       beq     .L4
-       adds    r3, r0, #1
        beq     .L1
+       adds    r3, r0, #1
+       beq     .L4
        subs    r0, r0, r4
        beq     .L4
        str     r4, [r6]
+       movs    r4, #0
        str     r0, [r5]
-       movs    r0, #0
 .L1:
+       mov     r0, r4
        pop     {r3, r4, r5, r6, r7, pc}
 .L4:
-       mov     r0, #-1
+       mov     r4, #-1
        b       .L1

well ...  .optimized change:

--- a/pr43920-2.c.250t.optimized        2021-11-18 10:32:22.951744385 +0100
+++ b/pr43920-2.c.250t.optimized        2021-11-18 10:31:56.739398949 +0100
@@ -39,7 +39,7 @@
   *length__13(D) = length_10;

   <bb 6> [local count: 1073741824]:
-  # _2 = PHI <end_9(3), 0(5), start_7(2), -1(4)>
+  # _2 = PHI <start_7(2), 0(5), end_9(3), -1(4)>
   return _2;

 }

-Coalesce list: (2)_2 & (9)end_9 [map: 0, 3] : Success -> 0
-Coalesce list: (2)_2 & (7)start_7 [map: 0, 2] : Fail due to conflict
+Coalesce list: (2)_2 & (7)start_7 [map: 0, 2] : Success -> 0
+Coalesce list: (2)_2 & (9)end_9 [map: 0, 3] : Fail due to conflict

-Inserting a partition copy on edge BB2->BB6 : PART.1 = PART.3
+Inserting a partition copy on edge BB3->BB6 : PART.1 = PART.3

looks like a fuss to me (fragile testcase).  Not sure if it is worth trying
to for example sort PHI args after SSA name version for increased stability,
at RTL expansion time we have exactly the same number of copies but I guess
(just guess) that at RA time things start to differ.

Again, ARM folks - please allow for the extra reg copy.

> arm-none-linux-gnueabi -march=armv5t -mthumb:
> FAIL: gcc.dg/tree-ssa/if-to-switch-3.c scan-tree-dump iftoswitch "Condition
> chain with [^\n\r]* BBs transformed into a switch statement."

should be fixed now.

[Bug testsuite/103298] [12 regressions] regressions on arm after r12-5301

[rearnsha at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103298

--- Comment #4 from Richard Earnshaw <rearnsha at gcc dot gnu.org> ---
The test looks fragile.

The instructions TBB and TBH can only support forward branches.  If a label in
the list of switch targets is backwards then they can't be used and a
non-compressed table must be used.

My guess is that what's happening here is that with other changes to the code
generation all the branches are now forwards and that the TBB/TBH optimisation
can be legitimately applied.

[Bug testsuite/103298] [12 regressions] regressions on arm after r12-5301

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103298

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|12.0                        |12.2

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 12.1 is being released, retargeting bugs to GCC 12.2.

[Bug testsuite/103298] [12 regressions] regressions on arm after r12-5301

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103298

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|12.3                        |12.4

--- Comment #7 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 12.3 is being released, retargeting bugs to GCC 12.4.