From: Taylor Simpson <ltaylorsimp...@gmail.com>
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 <ltaylorsimp...@gmail.com>
Reviewed-by: Brian Cain <bc...@quicinc.com>
Message-Id: <20240201103340.119081-3-ltaylorsimp...@gmail.com>
Signed-off-by: Brian Cain <bc...@quicinc.com>
---
target/hexagon/translate.c | 21 ++++-----------------
target/hexagon/translate.h | 13 +++++++------
2 files changed, 11 insertions(+), 23 deletions(-)
diff --git a/target/hexagon/translate.c b/target/hexagon/translate.c
index 47a870f42d..8d42ebd91c 100644
--- a/target/hexagon/translate.c
+++ b/target/hexagon/translate.c
@@ -1,5 +1,5 @@
/*
- * Copyright(c) 2019-2023 Qualcomm Innovation Center, Inc. All Rights
Reserved.
+ * Copyright(c) 2019-2024 Qualcomm Innovation Center, Inc. All Rights
Reserved.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
@@ -396,20 +396,8 @@ static bool need_commit(DisasContext *ctx)
}
}
- /* Check for overlap between register reads and writes */
- for (int i = 0; i < ctx->reg_log_idx; i++) {
- int rnum = ctx->reg_log[i];
- if (test_bit(rnum, ctx->regs_read)) {
- return true;
- }
- }
-
- /* Check for overlap between predicate reads and writes */
- for (int i = 0; i < ctx->preg_log_idx; i++) {
- int pnum = ctx->preg_log[i];
- if (test_bit(pnum, ctx->pregs_read)) {
- return true;
- }
+ if (ctx->read_after_write) {
+ return true;
}
/* Check for overlap between HVX reads and writes */
@@ -468,6 +456,7 @@ static void analyze_packet(DisasContext *ctx)
{
Packet *pkt = ctx->pkt;
ctx->has_hvx_helper = false;
+ ctx->read_after_write = false;
for (int i = 0; i < pkt->num_insns; i++) {
Insn *insn = &pkt->insn[i];
ctx->insn = insn;
@@ -492,11 +481,9 @@ static void gen_start_packet(DisasContext *ctx)
ctx->next_PC = next_PC;
ctx->reg_log_idx = 0;
bitmap_zero(ctx->regs_written, TOTAL_PER_THREAD_REGS);
- bitmap_zero(ctx->regs_read, TOTAL_PER_THREAD_REGS);
bitmap_zero(ctx->predicated_regs, TOTAL_PER_THREAD_REGS);
ctx->preg_log_idx = 0;
bitmap_zero(ctx->pregs_written, NUM_PREGS);
- bitmap_zero(ctx->pregs_read, NUM_PREGS);
ctx->future_vregs_idx = 0;
ctx->tmp_vregs_idx = 0;
ctx->vreg_log_idx = 0;
diff --git a/target/hexagon/translate.h b/target/hexagon/translate.h
index f06d71fc53..d5e7f49ad8 100644
--- a/target/hexagon/translate.h
+++ b/target/hexagon/translate.h
@@ -38,12 +38,10 @@ typedef struct DisasContext {
int reg_log[REG_WRITES_MAX];
int reg_log_idx;
DECLARE_BITMAP(regs_written, TOTAL_PER_THREAD_REGS);
- DECLARE_BITMAP(regs_read, TOTAL_PER_THREAD_REGS);
DECLARE_BITMAP(predicated_regs, TOTAL_PER_THREAD_REGS);
int preg_log[PRED_WRITES_MAX];
int preg_log_idx;
DECLARE_BITMAP(pregs_written, NUM_PREGS);
- DECLARE_BITMAP(pregs_read, NUM_PREGS);
uint8_t store_width[STORES_MAX];
bool s1_store_processed;
int future_vregs_idx;
@@ -68,6 +66,7 @@ typedef struct DisasContext {
bool is_tight_loop;
bool short_circuit;
bool has_hvx_helper;
+ bool read_after_write;
TCGv new_value[TOTAL_PER_THREAD_REGS];
TCGv new_pred_value[NUM_PREGS];
TCGv pred_written;
@@ -88,13 +87,14 @@ static inline void ctx_log_pred_write(DisasContext *ctx,
int pnum)
static inline void ctx_log_pred_read(DisasContext *ctx, int pnum)
{
- set_bit(pnum, ctx->pregs_read);
+ if (test_bit(pnum, ctx->pregs_written)) {
+ ctx->read_after_write = true;
+ }
}
static inline void ctx_log_pred_read_new(DisasContext *ctx, int pnum)
{
g_assert(test_bit(pnum, ctx->pregs_written));
- set_bit(pnum, ctx->pregs_read);
}
static inline void ctx_log_reg_write(DisasContext *ctx, int rnum,
@@ -125,13 +125,14 @@ static inline void ctx_log_reg_write_pair(DisasContext
*ctx, int rnum,
static inline void ctx_log_reg_read(DisasContext *ctx, int rnum)
{
- set_bit(rnum, ctx->regs_read);
+ if (test_bit(rnum, ctx->regs_written)) {
+ ctx->read_after_write = true;
+ }
}
static inline void ctx_log_reg_read_new(DisasContext *ctx, int rnum)
{
g_assert(test_bit(rnum, ctx->regs_written));
- set_bit(rnum, ctx->regs_read);
}
static inline void ctx_log_reg_read_pair(DisasContext *ctx, int rnum)
--
2.25.1
