Out-of-range shifts have undefined results, but must not trap.
Mask off immediate shift counts to solve this problem.
This bug can be reproduced by running the following guest instructions:
xor %ecx,%ecx
sar %cl,%eax
cmovne %edi,%eax
After optimization, the tcg opcodes of the sar are
movi_i32 tmp3,$0xffffffffffffffff pref=all
sar_i32 tmp3,eax,tmp3 dead: 2 pref=all
mov_i32 cc_dst,eax sync: 0 dead: 1 pref=0xffc0300
mov_i32 cc_src,tmp3 sync: 0 dead: 0 1 pref=all
movi_i32 cc_op,$0x31 sync: 0 dead: 0 pref=all
The sar_i32 opcode is a shift by -1, which unmasked generates
0x200808d618: fffa5b9b illegal
Signed-off-by: Zihao Yu <yuzihao@ict.ac.cn>
Message-Id: <20201216081206.9628-1-yuzihao@ict.ac.cn>
[rth: Reworded the patch description.]
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
d2f3066eb2