Re: [PATCH v2 09/30] tcg/loongarch64: Implement tcg_out_mov and tcg_out_movi

[Richard Henderson]

On 9/21/21 1:18 PM, WANG Xuerui wrote:
> +    /* Test for PC-relative values that can be loaded faster.  */
> +    intptr_t pc_offset = val - (uintptr_t)s->code_ptr;

This isn't quite right for split r^x code buffer.
You should have seen this with --enable-debug-tcg...

You need pc_offset = tcg_pcrel_diff(s, (void *)val).

> +    if (pc_offset == (int32_t)pc_offset) {
> +        tcg_target_long lo = sextreg(pc_offset, 0, 12);
> +        tcg_target_long hi = pc_offset - lo;
> +        tcg_out_opc_pcaddu12i(s, rd, hi >> 12);

And... this doesn't quite work, right at the edges.  If lo is negative, hi can overflow 
out of range.  There are a number of ways to fix this.  One is to extract the pieces and 
re-assemble to see if it matches.  Another is to rearrange the arithmetic just a little 
and use PCALAU12I.

> +    tcg_target_long upper = (val >> 12) & 0xfffff;
> +    tcg_target_long higher = (val >> 32) & 0xfffff;

Better to use extract64(val, 12, 20) and extract64(val, 32, 30).


r~