On 2022/10/12 19:34, WANG Xuerui wrote:
+ tcg_insn_unit i1, i2;
+
+ ptrdiff_t offset = addr - jmp_rx;
+
+ if (offset == sextreg(offset, 0, 28)) {
+ i1 = OPC_B | ((offset >> 18) & 0x3ff) | ((offset << 8) &
0x3fffc00);
Use encode_sd10k16_insn instead. No need to juggle the bits yourself
and you get nice range assertion for free.
+ i2 = NOP;
One more thing. I think there's a certain trend of making sure
potentially bad things don't happen and stopping speculative insn
fetch/execution by making the NOP here a BREAK instead. Although I'm not
sure if LoongArch or TCG is affected by the various speculation
vulnerabilities out there, to any degree, it might not hurt to just make
it a BREAK? Performance shouldn't get affected in any way but one could
probably sleep better with a guaranteed termination of execution flow
after the B.
And you should change the "tcg_out32(s, NOP)" some lines above into just
a "tcg_out_andi(s, 0, 0, 0)". This way you wouldn't have to define a NOP
constant at all... Or, maybe better, make a "tcg_out_nop" helper right
after the insn-defs include and after the "TCG intrinsics" section (it
isn't one, but there isn't a better place), then use it here, so you get
to include some more comments while still not having to define a NOP. Like:
static void tcg_out_nop(TCGContext *s)
{
/* Conventional NOP in LoongArch is `andi zero, zero, 0`. */
tcg_out_opc_andi(s, 0, 0, 0);
}
