[Bug target/123414] New: [16 Regression] [RISCV] [Miscompile] GCC - riscv64 target, miscompiles at -O3 since https://gcc.gnu.org/cgit/gcc/commit/?h=trunk&id=f5ddd4ba0ba

[skothadiya at whileone dot in via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123414

            Bug ID: 123414
           Summary: [16 Regression] [RISCV] [Miscompile] GCC - riscv64
                    target, miscompiles at -O3 since
                    https://gcc.gnu.org/cgit/gcc/commit/?h=trunk&id=f5ddd4
                    ba0ba
           Product: gcc
           Version: 16.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: skothadiya at whileone dot in
  Target Milestone: ---

Description:
The C code involve for loops on an unsigned, int, long & signed char, compiles
correctly on x86_64 and produces the expected output. However, when compiled
for the riscv64 architecture, the resulting binary yields an incorrect value.
The expected output is 34, but the program returns 0. This miscompilation
occurs specifically with optimization enabled at level -O3.

Compiler flags:
-march=rv64gcv_zvl1024b -flto  -mrvv-max-lmul=m8 -O3

Reproduction Steps:
1. Compile the test case with GCC for riscv64 using the -O3 flag.
2. Execute the compiled binary.
3. Observe the output.


COMMANDS:
/mnt/data1/sujayk/cifuzz-pad/riscv-gnu-toolchain-build/bin/riscv64-unknown-linux-gnu-gcc
-march=rv64gcv_zvl1024b -flto -mrvv-max-lmul=m8 -O3 red.c -o user-config.out
-fsigned-char -fno-strict-aliasing -fwrapv -Wno-unknown-warning-option -Werror
-Wfatal-errors -Wall -Wformat -Wno-int-in-bool-context -Wno-dangling-pointer
-Wno-compare-distinct-pointer-types -Wno-overflow -Wuninitialized
-Warray-bounds -Wreturn-type -Wno-unused-function -Wno-unused-variable
-Wno-unused-but-set-variable -Wno-unused-value -Wno-address -Wno-bool-compare
-Wno-pointer-sign -Wno-bool-operation -Wno-tautological-compare
-Wno-self-assign -Wno-implicit-const-int-float-conversion
-Wno-constant-conversion -Wno-unused-value
-Wno-tautological-constant-out-of-range-compare -Wno-constant-logical-operand
-Wno-parentheses-equality -Wno-pointer-sign

gcc -O1 red.c -o native.out -fno-strict-aliasing -fwrapv -w

QEMU_CPU=rv64,vlen=1024,rvv_ta_all_1s=true,rvv_ma_all_1s=true,v=true,vext_spec=v1.0,zve32f=true,zve64f=true
timeout --verbose -k 0.1 4
/mnt/data1/sujayk/cifuzz-pad/riscv-gnu-toolchain-build/bin/qemu-riscv64
user-config.out 1
0
timeout --verbose -k 0.1 1 ./native.out 1
34

  //Expected Output: 34
  //Actual Output: 0


-- testcase (red.c) --

int printf( const char *, ...);

signed char a=2;
long long b;
long c = 93;
int e[1][9];
void g( long cc, int ee[][9]) {
  for (int i=0; i<4; i++)
    for (int j=0; j<5; j++)
      for (unsigned k=0; k<9; k++) {
        a *= cc;
        for (int l=0; l<6; l+=(ee[k]<=0)+2)
          ;
      }
}

int main() {
  g( c, e);
  b = (int)a;
  printf("%llu\n", b);
}