> -----Original Message-----
> From: Richard Henderson <richard.henderson@linaro.org>
> Sent: Friday, March 3, 2023 3:31 PM
> To: qemu-devel@nongnu.org
> Cc: anjo@rev.ng; Taylor Simpson <tsimpson@quicinc.com>
> Subject: [PATCH 0/2] tcg: Merge two sequential labels
>
> WARNING: This email originated from outside of Qualcomm. Please be wary
> of any links or attachments, and do not enable macros.
>
> Supercedes: 20230301142221.24495-1-anjo@rev.ng
> ("[PATCH] tcg: `reachable_code_pass()` remove empty else-branch")
>
> Anton has probably seen this already but his patch now has conflicts with
> master. Rather than a while loop looking back across labels, let's fold all
> adjacent labels into a single label, at which point the current branch-to-next
> optimization works as is.
>
> Perhaps I missed it, but I didn't see how to reproduce the issue being
> resolved by the hexagon front end? So I haven't this trigger, but it passes
> the testsuite. :-)
>
>
> r~
Hi Richard,
Thanks!!
You need this series of patches to see this pattern from Hexagon
https://patchew.org/QEMU/20230131225647.25274-1-tsimpson@quicinc.com/
I have an update to that series for your tcg_temp_local_* series, but I'm wondering if I should wait for your tcg_temp_free patches to land first. Please advise.
Anyway, I tested your patch, and can see the optimization happening. Here is the input code and unoptimized TCG:
----------------
IN:
0x00400094: 0xf900c102 { if (P0) R2 = and(R0,R1) }
OP:
ld_i32 loc0,env,$0xfffffffffffffff0
brcond_i32 loc0,$0x0,lt,$L0
---- 00400094
and_i32 loc2,p0,$0x1
brcond_i32 loc2,$0x0,eq,$L1
and_i32 loc4,r0,r1
mov_i32 r2,loc4
br $L2
set_label $L1
set_label $L2
add_i32 pkt_cnt,pkt_cnt,$0x1
add_i32 insn_cnt,insn_cnt,$0x1
mov_i32 pc,$0x400098
exit_tb $0x0
set_label $L0
exit_tb $0x7fea80000043
Here is the optimized TCG after your patches. The two labels have been merged, and the unnecessary branch has been removed.
OP after optimization and liveness analysis:
ld_i32 tmp0,env,$0xfffffffffffffff0 dead: 1 pref=0xffff
brcond_i32 tmp0,$0x0,lt,$L0 dead: 0
---- 00400094
and_i32 tmp2,p0,$0x1 dead: 1 2 pref=0xffff
brcond_i32 tmp2,$0x0,eq,$L2 dead: 0 1
and_i32 tmp4,r0,r1 dead: 1 2 pref=0xffff
mov_i32 r2,tmp4 sync: 0 dead: 0 1 pref=0xffff
set_label $L2
add_i32 pkt_cnt,pkt_cnt,$0x1 sync: 0 dead: 0 1 pref=0xffff
add_i32 insn_cnt,insn_cnt,$0x1 sync: 0 dead: 0 1 2 pref=0xffff
mov_i32 pc,$0x400098 sync: 0 dead: 0 1 pref=0xffff
exit_tb $0x0
set_label $L0
exit_tb $0x7fea80000043
Tested-by: Taylor Simpson <tsimpson@quicinc.com>