qemu /
qemu /
bd983f68acad895d75678828d23e90ffeac58eea Hexagon (target/hexagon) Enable more short-circuit packets (scalar core)
Look for read-after-write instead of overlap of reads and writes
Here is an example with overalp but no read-after-write:
0x000200fc: 0x38103876 { R0 = add(R0,R1); R6 = add(R6,R7) }
BEFORE:
---- 00000000000200fc
mov_i32 loc2,$0x0
mov_i32 loc2,r0
add_i32 loc3,loc2,r1
mov_i32 loc2,loc3
mov_i32 loc4,$0x0
mov_i32 loc4,r6
add_i32 loc5,loc4,r7
mov_i32 loc4,loc5
mov_i32 r0,loc2
mov_i32 r6,loc4
AFTER:
---- 00000000000200fc
add_i32 loc2,r0,r1
mov_i32 r0,loc2
add_i32 loc3,r6,r7
mov_i32 r6,loc3
We can also short-circuit packets with .new values by reading from the
real destination instead of the temporary.
0x00020100: 0x78005ff3 { R19 = #0xff
0x00020104: 0x2002e204 if (cmp.eq(N19.new,R2)) jump:t PC+8 }
BEFORE:
---- 0000000000020100
mov_i32 pc,$0x20108
mov_i32 loc8,$0x0
mov_i32 loc8,$0xff
setcond_i32 loc10,loc8,r2,eq
mov_i32 loc6,loc10
mov_i32 r19,loc8
add_i32 pkt_cnt,pkt_cnt,$0x2
add_i32 insn_cnt,insn_cnt,$0x4
brcond_i32 loc6,$0x0,eq,$L1
goto_tb $0x0
mov_i32 pc,$0x20108
exit_tb $0x7fbb54000040
set_label $L1
goto_tb $0x1
exit_tb $0x7fbb54000041
set_label $L0
exit_tb $0x7fbb54000043
AFTER:
---- 0000000000020100
mov_i32 pc,$0x20108
mov_i32 r19,$0xff
setcond_i32 loc7,r19,r2,eq
mov_i32 loc4,loc7
add_i32 pkt_cnt,pkt_cnt,$0x2
add_i32 insn_cnt,insn_cnt,$0x4
brcond_i32 loc4,$0x0,eq,$L1
goto_tb $0x0
mov_i32 pc,$0x20108
exit_tb $0x7f9764000040
set_label $L1
goto_tb $0x1
exit_tb $0x7f9764000041
set_label $L0
exit_tb $0x7f9764000043
Signed-off-by: Taylor Simpson <ltaylorsimpson@gmail.com>
Reviewed-by: Brian Cain <bcain@quicinc.com>
Message-Id: <20240201103340.119081-3-ltaylorsimpson@gmail.com>
Signed-off-by: Brian Cain <bcain@quicinc.com>
2 files changed
