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* [Bug rtl-optimization/91865] Combine misses opportunity to remove (sign_extend (zero_extend)) before searching for insn patterns
[not found] <bug-91865-4@http.gcc.gnu.org/bugzilla/>
@ 2021-05-04 12:31 ` rguenth at gcc dot gnu.org
2023-10-26 9:11 ` cvs-commit at gcc dot gnu.org
2023-11-12 15:44 ` roger at nextmovesoftware dot com
2 siblings, 0 replies; 3+ messages in thread
From: rguenth at gcc dot gnu.org @ 2021-05-04 12:31 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91865
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |ASSIGNED
^ permalink raw reply [flat|nested] 3+ messages in thread
* [Bug rtl-optimization/91865] Combine misses opportunity to remove (sign_extend (zero_extend)) before searching for insn patterns
[not found] <bug-91865-4@http.gcc.gnu.org/bugzilla/>
2021-05-04 12:31 ` [Bug rtl-optimization/91865] Combine misses opportunity to remove (sign_extend (zero_extend)) before searching for insn patterns rguenth at gcc dot gnu.org
@ 2023-10-26 9:11 ` cvs-commit at gcc dot gnu.org
2023-11-12 15:44 ` roger at nextmovesoftware dot com
2 siblings, 0 replies; 3+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2023-10-26 9:11 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91865
--- Comment #6 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Roger Sayle <sayle@gcc.gnu.org>:
https://gcc.gnu.org/g:d1bb9569d7030490fe7bb35af432f934560d689d
commit r14-4941-gd1bb9569d7030490fe7bb35af432f934560d689d
Author: Roger Sayle <roger@nextmovesoftware.com>
Date: Thu Oct 26 10:06:59 2023 +0100
PR 91865: Avoid ZERO_EXTEND of ZERO_EXTEND in make_compound_operation.
This patch is my proposed solution to PR rtl-optimization/91865.
Normally RTX simplification canonicalizes a ZERO_EXTEND of a ZERO_EXTEND
to a single ZERO_EXTEND, but as shown in this PR it is possible for
combine's make_compound_operation to unintentionally generate a
non-canonical ZERO_EXTEND of a ZERO_EXTEND, which is unlikely to be
matched by the backend.
For the new test case:
const int table[2] = {1, 2};
int foo (char i) { return table[i]; }
compiling with -O2 -mlarge on msp430 we currently see:
Trying 2 -> 7:
2: r25:HI=zero_extend(R12:QI)
REG_DEAD R12:QI
7: r28:PSI=sign_extend(r25:HI)#0
REG_DEAD r25:HI
Failed to match this instruction:
(set (reg:PSI 28 [ iD.1772 ])
(zero_extend:PSI (zero_extend:HI (reg:QI 12 R12 [ iD.1772 ]))))
which results in the following code:
foo: AND #0xff, R12
RLAM.A #4, R12 { RRAM.A #4, R12
RLAM.A #1, R12
MOVX.W table(R12), R12
RETA
With this patch, we now see:
Trying 2 -> 7:
2: r25:HI=zero_extend(R12:QI)
REG_DEAD R12:QI
7: r28:PSI=sign_extend(r25:HI)#0
REG_DEAD r25:HI
Successfully matched this instruction:
(set (reg:PSI 28 [ iD.1772 ])
(zero_extend:PSI (reg:QI 12 R12 [ iD.1772 ])))
allowing combination of insns 2 and 7
original costs 4 + 8 = 12
replacement cost 8
foo: MOV.B R12, R12
RLAM.A #1, R12
MOVX.W table(R12), R12
RETA
2023-10-26 Roger Sayle <roger@nextmovesoftware.com>
Richard Biener <rguenther@suse.de>
gcc/ChangeLog
PR rtl-optimization/91865
* combine.cc (make_compound_operation): Avoid creating a
ZERO_EXTEND of a ZERO_EXTEND.
gcc/testsuite/ChangeLog
PR rtl-optimization/91865
* gcc.target/msp430/pr91865.c: New test case.
^ permalink raw reply [flat|nested] 3+ messages in thread
* [Bug rtl-optimization/91865] Combine misses opportunity to remove (sign_extend (zero_extend)) before searching for insn patterns
[not found] <bug-91865-4@http.gcc.gnu.org/bugzilla/>
2021-05-04 12:31 ` [Bug rtl-optimization/91865] Combine misses opportunity to remove (sign_extend (zero_extend)) before searching for insn patterns rguenth at gcc dot gnu.org
2023-10-26 9:11 ` cvs-commit at gcc dot gnu.org
@ 2023-11-12 15:44 ` roger at nextmovesoftware dot com
2 siblings, 0 replies; 3+ messages in thread
From: roger at nextmovesoftware dot com @ 2023-11-12 15:44 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91865
Roger Sayle <roger at nextmovesoftware dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |roger at nextmovesoftware dot com
Status|ASSIGNED |RESOLVED
Resolution|--- |FIXED
--- Comment #7 from Roger Sayle <roger at nextmovesoftware dot com> ---
This should now be fixed on mainline.
^ permalink raw reply [flat|nested] 3+ messages in thread
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