[Bug c/110281] New: wrong code with '-O3'

[Bug c/110281] New: wrong code with '-O3'

[19373742 at buaa dot edu.cn]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110281

            Bug ID: 110281
           Summary: wrong code with '-O3'
           Product: gcc
           Version: 11.4.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: 19373742 at buaa dot edu.cn
  Target Milestone: ---

Created attachment 55341
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=55341&action=edit
The preprocessed file

*******************************************************************************
OS and Platform:
CentOS Linux release 7.9.2009 (Core), x86_64 GNU/Linux
*******************************************************************************
gcc version:

# /home/gcc-releases/gcc-11-0615/bin/gcc -v
Using built-in specs.
COLLECT_GCC=/home/gcc-releases/gcc-11-0615/bin/gcc
COLLECT_LTO_WRAPPER=/home/gcc-releases/gcc-11-0615/libexec/gcc/x86_64-pc-linux-gnu/11.4.1/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ./configure --prefix=/home/gcc-releases/gcc-11-0615/
--disable-multilib --enable-languages=c,c++
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 11.4.1 20230615 (GCC)
*******************************************************************************
Command Lines:
/home/gcc-releases/gcc-11-0615/bin/gcc -I
/home/csmith_record/include/csmith-2.3.0/ -O3
-fno-aggressive-loop-optimizations -fno-align-functions -fno-align-jumps
-fno-align-labels -fno-align-loops -fno-allocation-dce
-fno-asynchronous-unwind-tables -fno-auto-inc-dec -fno-bit-tests
-fno-branch-count-reg -fno-caller-saves -fno-code-hoisting
-fno-combine-stack-adjustments -fno-compare-elim -fno-cprop-registers
-fno-crossjumping -fno-cse-follow-jumps -fno-dce -fno-defer-pop
-fno-delete-null-pointer-checks -fno-devirtualize
-fno-devirtualize-speculatively -fno-dse -fno-early-inlining
-fno-expensive-optimizations -fno-forward-propagate -fno-fp-int-builtin-inexact
-fno-function-cse -fno-gcse -fno-gcse-after-reload -fno-gcse-lm
-fno-guess-branch-probability -fno-hoist-adjacent-loads -fno-if-conversion
-fno-if-conversion2 -fno-indirect-inlining -fno-inline -fno-inline-atomics
-fno-inline-functions -fno-inline-functions-called-once
-fno-inline-small-functions -fno-ipa-bit-cp -fno-ipa-cp -fno-ipa-cp-clone
-fno-ipa-icf -fno-ipa-icf-functions -fno-ipa-icf-variables -fno-ipa-modref
-fno-ipa-profile -fno-ipa-pure-const -fno-ipa-ra -fno-ipa-reference
-fno-ipa-reference-addressable -fno-ipa-sra -fno-ipa-stack-alignment
-fno-ipa-vrp -fno-ira-hoist-pressure -fno-ira-share-save-slots
-fno-ira-share-spill-slots -fno-isolate-erroneous-paths-dereference -fno-ivopts
-fno-jump-tables -fno-lifetime-dse -fno-loop-interchange
-fno-loop-unroll-and-jam -fno-lra-remat -fno-math-errno
-fno-move-loop-invariants -fno-omit-frame-pointer -fno-optimize-sibling-calls
-fno-optimize-strlen -fno-partial-inlining -fno-peel-loops -fno-peephole
-fno-peephole2 -fno-plt -fno-predictive-commoning -fno-prefetch-loop-arrays
-fno-printf-return-value -fno-ree -fno-reg-struct-return -fno-rename-registers
-fno-reorder-blocks -fno-reorder-blocks-and-partition -fno-reorder-functions
-fno-rerun-cse-after-loop -fno-sched-critical-path-heuristic
-fno-sched-dep-count-heuristic -fno-sched-group-heuristic -fno-sched-interblock
-fno-sched-last-insn-heuristic -fno-sched-rank-heuristic -fno-sched-spec
-fno-sched-spec-insn-heuristic -fno-sched-stalled-insns-dep
-fno-schedule-fusion -fno-schedule-insns2 -fno-short-enums -fno-shrink-wrap
-fno-shrink-wrap-separate -fno-signed-zeros -fno-split-ivs-in-unroller
-fno-split-loops -fno-split-paths -fno-split-wide-types -fno-ssa-backprop
-fno-ssa-phiopt -fno-stdarg-opt -fno-store-merging -fno-strict-aliasing
-fno-strict-volatile-bitfields -fno-thread-jumps -fno-toplevel-reorder
-fno-trapping-math -fno-tree-bit-ccp -fno-tree-builtin-call-dce -fno-tree-ccp
-fno-tree-ch -fno-tree-coalesce-vars -fno-tree-copy-prop -fno-tree-cselim
-fno-tree-dce -fno-tree-dominator-opts -fno-tree-dse -fno-tree-forwprop
-fno-tree-fre -fno-tree-loop-distribute-patterns -fno-tree-loop-distribution
-fno-tree-loop-if-convert -fno-tree-loop-im -fno-tree-loop-ivcanon
-fno-tree-loop-optimize -fno-tree-loop-vectorize -fno-tree-partial-pre
-fno-tree-phiprop -fno-tree-pre -fno-tree-pta -fno-tree-reassoc
-fno-tree-scev-cprop -fno-tree-sink -fno-tree-slp-vectorize -fno-tree-slsr
-fno-tree-sra -fno-tree-switch-conversion -fno-tree-tail-merge -fno-tree-ter
-fno-tree-vrp -fno-unroll-completely-grow-size -fno-unswitch-loops
-fno-unwind-tables -fno-var-tracking -fno-var-tracking-assignments
-fno-version-loops-for-strides -fno-web -faggressive-loop-optimizations
-fno-align-functions -fno-align-jumps -falign-labels -fno-align-loops
-fno-allocation-dce -fasynchronous-unwind-tables -fauto-inc-dec -fbit-tests
-fno-branch-count-reg -fno-caller-saves -fno-code-hoisting
-fcombine-stack-adjustments -fcompare-elim -fno-cprop-registers -fcrossjumping
-fcse-follow-jumps -fdce -fno-defer-pop -fno-delete-null-pointer-checks
-fdevirtualize -fdevirtualize-speculatively -fdse -fno-early-inlining
-fno-expensive-optimizations -fno-forward-propagate -ffp-int-builtin-inexact
-ffunction-cse -fno-gcse -fno-gcse-after-reload -fgcse-lm
-fguess-branch-probability -fno-hoist-adjacent-loads -fif-conversion
-fif-conversion2 -fno-indirect-inlining -finline -finline-atomics
-finline-functions -finline-functions-called-once -finline-small-functions
-fipa-bit-cp -fno-ipa-cp -fno-ipa-cp-clone -fipa-icf -fipa-icf-functions
-fno-ipa-icf-variables -fipa-modref -fipa-profile -fno-ipa-pure-const
-fno-ipa-ra -fipa-reference -fipa-reference-addressable -fno-ipa-sra
-fno-ipa-stack-alignment -fno-ipa-vrp -fno-ira-hoist-pressure
-fno-ira-share-save-slots -fno-ira-share-spill-slots
-fno-isolate-erroneous-paths-dereference -fivopts -fno-jump-tables
-flifetime-dse -fno-loop-interchange -fno-loop-unroll-and-jam -flra-remat
-fmath-errno -fno-move-loop-invariants -fno-omit-frame-pointer
-fno-optimize-sibling-calls -fno-optimize-strlen -fpartial-inlining
-fpeel-loops -fno-peephole -fpeephole2 -fno-plt -fpredictive-commoning
-fprefetch-loop-arrays -fprintf-return-value -fno-ree -fno-reg-struct-return
-frename-registers -fno-reorder-blocks -freorder-blocks-and-partition
-freorder-functions -frerun-cse-after-loop -fsched-critical-path-heuristic
-fno-sched-dep-count-heuristic -fno-sched-group-heuristic -fno-sched-interblock
-fno-sched-last-insn-heuristic -fsched-rank-heuristic -fsched-spec
-fno-sched-spec-insn-heuristic -fno-sched-stalled-insns-dep -fschedule-fusion
-fschedule-insns2 -fshort-enums -fshrink-wrap -fshrink-wrap-separate
-fsigned-zeros -fno-split-ivs-in-unroller -fsplit-loops -fsplit-paths
-fsplit-wide-types -fno-ssa-backprop -fssa-phiopt -fno-stdarg-opt
-fstore-merging -fstrict-aliasing -fstrict-volatile-bitfields -fthread-jumps
-ftoplevel-reorder -ftrapping-math -ftree-bit-ccp -ftree-builtin-call-dce
-fno-tree-ccp -ftree-ch -ftree-coalesce-vars -ftree-copy-prop -ftree-cselim
-ftree-dce -ftree-dominator-opts -fno-tree-dse -ftree-forwprop -ftree-fre
-fno-tree-loop-distribute-patterns -ftree-loop-distribution
-ftree-loop-if-convert -ftree-loop-im -ftree-loop-ivcanon -ftree-loop-optimize
-fno-tree-loop-vectorize -fno-tree-partial-pre -ftree-phiprop -ftree-pre
-fno-tree-pta -fno-tree-reassoc -fno-tree-scev-cprop -fno-tree-sink
-ftree-slp-vectorize -fno-tree-slsr -fno-tree-sra -fno-tree-switch-conversion
-ftree-tail-merge -fno-tree-ter -fno-tree-vrp -fno-unroll-completely-grow-size
-funswitch-loops -fno-unwind-tables -fno-var-tracking
-fno-var-tracking-assignments -fno-version-loops-for-strides -fno-web
-save-temps t.c -o t.o 2>t_error.txt

# /home/gcc-releases/gcc-11-0615/bin/gcc -I
/home/csmith_record/include/csmith-2.3.0/ t.c -o t2.o

# ./t2.o
checksum = 85C697B
# ./t.o
checksum = E43ACEEF

[Bug c/110281] wrong code with '-O3'

[19373742 at buaa dot edu.cn]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110281

--- Comment #1 from CTC <19373742 at buaa dot edu.cn> ---
Created attachment 55342
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=55342&action=edit
The compiler output

[Bug middle-end/110281] wrong code with '-O3'

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110281

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to fail|                            |10.4.1, 11.3.0, 12.2.1,
                   |                            |13.1.1, 14.0
           Keywords|                            |wrong-code
             Target|                            |x86_64-*-*
          Component|c                           |middle-end

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
I can confirm a different checksum with GCC 10, 11, 12, 13 and trunk -O2 vs.
-O[01]

[Bug middle-end/110281] wrong code with '-O3'

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110281

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
-fno-strict-aliasing avoids the issue.

[Bug middle-end/110281] wrong code with '-O3'

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110281

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
clang produces the same behavior

[Bug middle-end/110281] wrong code with '-O3'

[19373742 at buaa dot edu.cn]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110281

--- Comment #5 from CTC <19373742 at buaa dot edu.cn> ---
Could you please do me a favor to confirm whether this phenomenon indicates a
bug or a normal behavior? Actually, I also found other optimization sequences
with -fstrict-aliasing which output 'checksum = 85C697B'. Thanks very much for
your efforts in advance!

[Bug middle-end/110281] wrong code with '-O3'

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110281

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org

--- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
That requires detailed analysis nobody performed yet.  csmith is known to
generate invalid programs sometimes, especially with some options, and only
such analysis can give definite answers.  Though, two independent compilers
behaving the same and -fno-strict-aliasing option making it go away is a strong
indication it could very well be a bug in the generated testcase.

[Bug middle-end/110281] wrong code with '-O3'

[19373742 at buaa dot edu.cn]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110281

--- Comment #7 from CTC <19373742 at buaa dot edu.cn> ---
(In reply to Jakub Jelinek from comment #6)
> That requires detailed analysis nobody performed yet.  csmith is known to
> generate invalid programs sometimes, especially with some options, and only
> such analysis can give definite answers.  Though, two independent compilers
> behaving the same and -fno-strict-aliasing option making it go away is a
> strong indication it could very well be a bug in the generated testcase.

Thanks very much for your explanation!

[Bug middle-end/110281] wrong code with '-O3'

[19373742 at buaa dot edu.cn]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110281

--- Comment #8 from CTC <19373742 at buaa dot edu.cn> ---
The issue can be reproduced with -O3 -fno-tree-dominator-opts -fno-tree-pre.