[Bug tree-optimization/116338] New: GCC is not vectoring TSVC s255 while clang can

[kugan at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116338

            Bug ID: 116338
           Summary: GCC is not vectoring TSVC s255 while clang can
           Product: gcc
           Version: 15.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: kugan at gcc dot gnu.org
  Target Milestone: ---

reduced test case:

typedef float real_t;
extern __attribute__((aligned(64))) real_t a[32000], b[32000];

void s255()
{   
    real_t x, y;
    x = b[32000 -1];
    y = b[32000 -2];
    for (int i = 0; i < 32000; i++) {
        a[i] = (b[i] + x + y) * (real_t).333;
        y = x;
        x = b[i];
    }

}

gcc is not able to vectorize the loop whereas clang can. See
https://godbolt.org/z/64Kxaahqr

gcc -v
Using built-in specs.
COLLECT_GCC=/home/kvivekananda/install/bin/gcc
COLLECT_LTO_WRAPPER=/home/kvivekananda/install/libexec/gcc/aarch64-unknown-linux-gnu/15.0.0/lto-wrapper
Target: aarch64-unknown-linux-gnu
Configured with: ../gcc_base/configure --prefix=/home/kvivekananda/install/
--enable-languages=c,c++,fortran,lto,objc
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 15.0.0 20240618 (experimental) (GCC)