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From: "zsojka at seznam dot cz" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/104604] New: wrong code with -O2
 -fconserve-stack --param=vrp1-mode=ranger
Date: Sat, 19 Feb 2022 07:55:17 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D104604

            Bug ID: 104604
           Summary: wrong code with -O2 -fconserve-stack
                    --param=3Dvrp1-mode=3Dranger
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: zsojka at seznam dot cz
  Target Milestone: ---
              Host: x86_64-pc-linux-gnu
            Target: x86_64-pc-linux-gnu

Created attachment 52479
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D52479&action=3Dedit
reduced testcase

Output:
$ x86_64-pc-linux-gnu-gcc -O2 -fconserve-stack --param=3Dvrp1-mode=3Dranger
testcase.c -Wno-psabi
$ ./a.out=20
Aborted

The value of x[] is {3, 3, 3, 3, ... }
It seems "i /=3D c;" got optimised out.

$ x86_64-pc-linux-gnu-gcc -v
Using built-in specs.
COLLECT_GCC=3D/repo/gcc-trunk/binary-latest-amd64/bin/x86_64-pc-linux-gnu-g=
cc
COLLECT_LTO_WRAPPER=3D/repo/gcc-trunk/binary-trunk-r12-7293-20220218075854-=
gfe79d652c96-checking-yes-rtl-df-extra-nobootstrap-amd64/bin/../libexec/gcc=
/x86_64-pc-linux-gnu/12.0.1/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: /repo/gcc-trunk//configure --enable-languages=3Dc,c++
--enable-valgrind-annotations --disable-nls --enable-checking=3Dyes,rtl,df,=
extra
--disable-bootstrap --with-cloog --with-ppl --with-isl
--build=3Dx86_64-pc-linux-gnu --host=3Dx86_64-pc-linux-gnu
--target=3Dx86_64-pc-linux-gnu --with-ld=3D/usr/bin/x86_64-pc-linux-gnu-ld
--with-as=3D/usr/bin/x86_64-pc-linux-gnu-as --disable-libstdcxx-pch
--prefix=3D/repo/gcc-trunk//binary-trunk-r12-7293-20220218075854-gfe79d652c=
96-checking-yes-rtl-df-extra-nobootstrap-amd64
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 12.0.1 20220218 (experimental) (GCC)=