[r16-6727 Regression] FAIL: gcc.dg/store_merging_19.c scan-tree-dump-times store-merging "Merging successful" 3 on Linux/x86_64

[Haochen Jiang]

On Linux/x86_64,

50df2b188450457580b5ff4ac1d524fcc74de9bc is the first bad commit
commit 50df2b188450457580b5ff4ac1d524fcc74de9bc
Author: Andrew Pinski <andrew.pinski@oss.qualcomm.com>
Date:   Sat Jan 10 23:17:12 2026 -0800

    match: Simplify `(T1)(a bit_op (T2)b)` to `((T1)a bit_op b)` When b is T1 type and truncating from T2 [PR122845]

caused

FAIL: gcc.dg/store_merging_19.c scan-tree-dump-times store-merging "Merging successful" 3

with GCC configured with

../../gcc/configure --prefix=/export/users3/haochenj/src/gcc-bisect/master/master/r16-6727/usr --enable-clocale=gnu --with-system-zlib --with-demangler-in-ld --with-fpmath=sse --enable-languages=c,c++,fortran --enable-cet --without-isl --enable-libmpx x86_64-linux --disable-bootstrap

To reproduce:

$ cd {build_dir}/gcc && make check RUNTESTFLAGS="dg.exp=gcc.dg/store_merging_19.c --target_board='unix{-m32}'"
$ cd {build_dir}/gcc && make check RUNTESTFLAGS="dg.exp=gcc.dg/store_merging_19.c --target_board='unix{-m32\ -march=cascadelake}'"
$ cd {build_dir}/gcc && make check RUNTESTFLAGS="dg.exp=gcc.dg/store_merging_19.c --target_board='unix{-m64}'"
$ cd {build_dir}/gcc && make check RUNTESTFLAGS="dg.exp=gcc.dg/store_merging_19.c --target_board='unix{-m64\ -march=cascadelake}'"

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(If you met problems with cascadelake related, disabling AVX512F in command line might save that.)
(However, please make sure that there is no potential problems with AVX512.)