target/i386: fix ADOX followed by ADCX

When ADCX is followed by ADOX or vice versa, the second instruction's
carry comes from EFLAGS and the condition codes use the CC_OP_ADCOX
operation.  Retrieving the carry from EFLAGS is handled by this bit
of gen_ADCOX:

        tcg_gen_extract_tl(carry_in, cpu_cc_src,
            ctz32(cc_op == CC_OP_ADCX ? CC_C : CC_O), 1);

Unfortunately, in this case cc_op has been overwritten by the previous
"if" statement to CC_OP_ADCOX.  This works by chance when the first
instruction is ADCX; however, if the first instruction is ADOX,
ADCX will incorrectly take its carry from OF instead of CF.

Fix by moving the computation of the new cc_op at the end of the function.
The included exhaustive test case fails without this patch and passes
afterwards.

Because ADCX/ADOX need not be invoked through the VEX prefix, this
regression bisects to commit 16fc5726a6e2 ("target/i386: reimplement
0x0f 0x38, add AVX", 2022-10-18).  However, the mistake happened a
little earlier, when BMI instructions were rewritten using the new
decoder framework.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1471
Reported-by: Paul Jolly <https://gitlab.com/myitcv>
Fixes: 1d0b926150e5 ("target/i386: move scalar 0F 38 and 0F 3A instruction to new decoder", 2022-10-18)
Cc: qemu-stable@nongnu.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

0 files changed, 0 insertions, 0 deletions