[Bug c/110683] New: wrong code with '-O2' and specific optimizations

[Bug c/110683] New: wrong code with '-O2' and specific optimizations

[19373742 at buaa dot edu.cn]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110683

            Bug ID: 110683
           Summary: wrong code with '-O2' and specific optimizations
           Product: gcc
           Version: 12.3.1
            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 55551
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=55551&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-12-0707/bin/gcc -v
Using built-in specs.
COLLECT_GCC=/home/gcc-releases/gcc-12-0707/bin/gcc
COLLECT_LTO_WRAPPER=/home/gcc-releases/gcc-12-0707/libexec/gcc/x86_64-pc-linux-gnu/12.3.1/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ./configure --prefix=/home/gcc-releases/gcc-12-0707/
--disable-multilib --enable-language=c,c++
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 12.3.1 20230707 (GCC)
*******************************************************************************
Command Lines:
# /home/gcc-releases/gcc-12-0707/bin/gcc -I
/home/csmith_record/include/csmith-2.3.0/  -O2
-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-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-strict-aliasing -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-move-loop-stores
-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-printf-return-value -fno-ree
-fno-reg-struct-return -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-semantic-interposition -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-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-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-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-version-loops-for-strides -fno-allow-store-data-races
-fno-associative-math -fno-branch-probabilities -fno-conserve-stack
-fno-cx-fortran-rules -fno-cx-limited-range -fno-delayed-branch
-fno-delete-dead-exceptions -fno-exceptions -fno-finite-loops
-fno-finite-math-only -fno-float-store -fno-gcse-las -fno-gcse-sm -fno-graphite
-fno-graphite-identity -fno-harden-compares -fno-harden-conditional-branches
-fno-ipa-pta -fno-ira-loop-pressure -fno-isolate-erroneous-paths-attribute
-fno-keep-gc-roots-live -fno-limit-function-alignment -fno-live-range-shrinkage
-fno-loop-nest-optimize -fno-loop-parallelize-all -fno-modulo-sched
-fno-modulo-sched-allow-regmoves -fno-non-call-exceptions -fno-opt-info
-fno-pack-struct -fno-profile-partial-training -fno-profile-reorder-functions
-fno-reciprocal-math -fno-rename-registers
-fno-reschedule-modulo-scheduled-loops -fno-rounding-math
-fno-save-optimization-record -fno-sched-pressure -fno-sched-spec-load
-fno-sched-spec-load-dangerous -fno-sched-stalled-insns
-fno-sched2-use-superblocks -fno-schedule-insns -fno-section-anchors
-fno-sel-sched-pipelining -fno-sel-sched-pipelining-outer-loops
-fno-sel-sched-reschedule-pipelined -fno-short-wchar -fno-signaling-nans
-fno-single-precision-constant -fno-split-wide-types-early
-fno-stack-clash-protection -fno-tracer -fno-trapv -fno-tree-cselim
-fno-tree-lrs -fno-tree-vectorize -fno-unconstrained-commons
-fno-unroll-all-loops -fno-unroll-loops -fno-unsafe-math-optimizations
-fno-var-tracking -fno-var-tracking-assignments
-fno-var-tracking-assignments-toggle -fno-var-tracking-uninit
-fno-variable-expansion-in-unroller -fno-vpt -fno-web -fno-wrapv
-fno-wrapv-pointer -gno-statement-frontiers -fno-aggressive-loop-optimizations
-falign-functions -falign-jumps -fno-align-labels -fno-align-loops
-fno-allocation-dce -fasynchronous-unwind-tables -fauto-inc-dec -fno-bit-tests
-fbranch-count-reg -fcaller-saves -fno-code-hoisting
-fno-combine-stack-adjustments -fno-compare-elim -fno-cprop-registers
-fno-crossjumping -fno-cse-follow-jumps -fdce -fdefer-pop -fno-devirtualize
-fno-devirtualize-speculatively -fno-dse -fearly-inlining
-fno-expensive-optimizations -fforward-propagate -ffp-int-builtin-inexact
-ffunction-cse -fno-gcse -fgcse-after-reload -fgcse-lm
-fguess-branch-probability -fno-hoist-adjacent-loads -fif-conversion
-fif-conversion2 -findirect-inlining -finline -finline-atomics
-finline-functions -finline-functions-called-once -fno-inline-small-functions
-fipa-bit-cp -fno-ipa-cp -fipa-cp-clone -fno-ipa-icf -fipa-icf-functions
-fipa-icf-variables -fipa-modref -fno-ipa-profile -fipa-pure-const -fno-ipa-ra
-fipa-reference -fno-ipa-reference-addressable -fno-ipa-sra
-fipa-stack-alignment -fipa-strict-aliasing -fno-ipa-vrp -fira-hoist-pressure
-fno-ira-share-save-slots -fira-share-spill-slots
-fisolate-erroneous-paths-dereference -fno-ivopts -fno-jump-tables
-flifetime-dse -floop-interchange -fno-loop-unroll-and-jam -fno-lra-remat
-fmath-errno -fno-move-loop-invariants -fmove-loop-stores -fomit-frame-pointer
-fno-optimize-sibling-calls -fno-optimize-strlen -fno-partial-inlining
-fno-peel-loops -fpeephole -fpeephole2 -fplt -fno-predictive-commoning
-fno-printf-return-value -fno-ree -freg-struct-return -fno-reorder-blocks
-freorder-blocks-and-partition -freorder-functions -fno-rerun-cse-after-loop
-fsched-critical-path-heuristic -fsched-dep-count-heuristic
-fsched-group-heuristic -fno-sched-interblock -fno-sched-last-insn-heuristic
-fno-sched-rank-heuristic -fsched-spec -fsched-spec-insn-heuristic
-fno-sched-stalled-insns-dep -fschedule-fusion -fschedule-insns2
-fsemantic-interposition -fshort-enums -fno-shrink-wrap
-fno-shrink-wrap-separate -fno-signed-zeros -fno-split-ivs-in-unroller
-fsplit-loops -fno-split-paths -fno-split-wide-types -fno-ssa-backprop
-fno-ssa-phiopt -fno-stdarg-opt -fstore-merging -fno-strict-aliasing
-fthread-jumps -fno-toplevel-reorder -fno-trapping-math -fno-tree-bit-ccp
-ftree-builtin-call-dce -ftree-ccp -fno-tree-ch -ftree-coalesce-vars
-ftree-copy-prop -ftree-dce -ftree-dominator-opts -fno-tree-dse
-fno-tree-forwprop -ftree-fre -ftree-loop-distribute-patterns
-ftree-loop-distribution -ftree-loop-im -ftree-loop-ivcanon
-fno-tree-loop-optimize -ftree-loop-vectorize -ftree-partial-pre -ftree-phiprop
-fno-tree-pre -ftree-pta -ftree-reassoc -fno-tree-scev-cprop -ftree-sink
-fno-tree-slp-vectorize -ftree-slsr -ftree-sra -fno-tree-switch-conversion
-ftree-tail-merge -fno-tree-ter -ftree-vrp -funroll-completely-grow-size
-fno-unswitch-loops -fno-unwind-tables -fversion-loops-for-strides
-fno-allow-store-data-races -fassociative-math -fbranch-probabilities
-fno-conserve-stack -fno-cx-fortran-rules -fno-cx-limited-range
-fdelayed-branch -fdelete-dead-exceptions -fno-exceptions -fno-finite-loops
-ffinite-math-only -fno-float-store -fno-gcse-las -fgcse-sm -fno-graphite
-fgraphite-identity -fharden-compares -fharden-conditional-branches
-fno-ipa-pta -fno-ira-loop-pressure -fno-isolate-erroneous-paths-attribute
-fkeep-gc-roots-live -fno-limit-function-alignment -fno-live-range-shrinkage
-fno-loop-nest-optimize -fno-loop-parallelize-all -fno-modulo-sched
-fno-modulo-sched-allow-regmoves -fnon-call-exceptions -fno-opt-info
-fpack-struct -fno-profile-partial-training -fno-profile-reorder-functions
-freciprocal-math -fno-rename-registers -freschedule-modulo-scheduled-loops
-frounding-math -fno-save-optimization-record -fsched-pressure
-fsched-spec-load -fsched-spec-load-dangerous -fno-sched-stalled-insns
-fsched2-use-superblocks -fno-schedule-insns -fno-section-anchors
-fno-sel-sched-pipelining -fno-sel-sched-pipelining-outer-loops
-fsel-sched-reschedule-pipelined -fno-short-wchar -fno-signaling-nans
-fsingle-precision-constant -fno-split-wide-types-early
-fno-stack-clash-protection -fno-tracer -ftrapv -fno-tree-cselim -fno-tree-lrs
-fno-tree-vectorize -fno-unconstrained-commons -funroll-all-loops
-funroll-loops -fno-unsafe-math-optimizations -fvar-tracking
-fvar-tracking-assignments -fno-var-tracking-assignments-toggle
-fno-var-tracking-uninit -fvariable-expansion-in-unroller -fno-vpt -fweb
-fno-wrapv -fwrapv-pointer -gstatement-frontiers -save-temps ms.c -o m3.o
2>m3.txt

# /home/gcc-releases/gcc-12-0707/bin/gcc -I /home/csmith/include/csmith-2.3.0/
ms.c -o m4.o

# ./m4.o
checksum = 16499F41
# ./m3.o
checksum = 187B9F46

[Bug c/110683] wrong code with '-O2' and specific optimizations

[19373742 at buaa dot edu.cn]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110683

--- Comment #1 from CTC <19373742 at buaa dot edu.cn> ---
Created attachment 55552
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=55552&action=edit
The compiler output

[Bug c/110683] wrong code with '-O2' and specific optimizations

[19373742 at buaa dot edu.cn]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110683

--- Comment #2 from CTC <19373742 at buaa dot edu.cn> ---
The reduced optimizations is -O2 -fpack-struct

[Bug c/110683] wrong code with '-O2 -fpack-struct'

[19373742 at buaa dot edu.cn]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110683

--- Comment #3 from CTC <19373742 at buaa dot edu.cn> ---
The reduced program is

# cat mss.i
struct a {
  char b;
  int c;
};
union {
  struct a b;
  short c;
} d = {8, 1};
void main() { printf("%d\n", d.c); }

[Bug c/110683] wrong code with '-O2 -fpack-struct'

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110683

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to CTC from comment #3)
> The reduced program is
> 
> # cat mss.i
> struct a {
>   char b;
>   int c;
> };
> union {
>   struct a b;
>   short c;
> } d = {8, 1};
> void main() { printf("%d\n", d.c); }

This reduced case shows that -fpacked-struct will change the layout of struct a
and nothing more. Without the option there is some padding bytes which are
zero. Also also this reduced testcase depends on the endian of the target.

Maybe the original testcase has similar issues with the unions.

[Bug c/110683] wrong code with '-O2 -fpack-struct'

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110683

--- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
ms.c:299:24: warning: taking address of packed member of 'union U1' may result
in an unaligned pointer value [-Waddress-of-packed-member]

[Bug c/110683] wrong code with '-O2 -fpack-struct'

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110683

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |INVALID

--- Comment #6 from Richard Biener <rguenth at gcc dot gnu.org> ---
There's a set of options like -fpack-struct that result in a non 1:1 transform
of the program which you probably should avoid using.  In the manual they are
documented to change the ABI.