https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113070
--- Comment #7 from Alex Coplan <acoplan at gcc dot gnu.org> ---
Just to give a concrete example / reduced testcase where this goes wrong (to
aid review). For the following testcase (reduced from libiberty) with -O2
-mlate-ldp-fusion:
struct {
unsigned D;
int E;
} * sha1_process_block_ctx;
void *sha1_process_block_buffer;
int sha1_process_block_ctx_1, sha1_process_block_ctx_0,
sha1_process_block_ctx_3, sha1_process_block_d, sha1_process_block_e,
sha1_process_block_tm, sha1_process_block_a, sha1_process_block_x_6,
sha1_process_block_x_14, sha1_process_block_x_15;
unsigned sha1_process_block_ctx_2;
void sha1_process_block() {
int *words = sha1_process_block_buffer;
int endp = *words, x_0;
int x[6];
unsigned b, c;
while (endp) {
int t = 0;
for (; t < 6;)
t = *words;
sha1_process_block_a +=
sha1_process_block_ctx_2 + 8348 + sha1_process_block_tm;
x_0 += sha1_process_block_tm = x[73];
b += sha1_process_block_x_15 = sha1_process_block_tm;
sha1_process_block_a += b | 1;
sha1_process_block_tm = sha1_process_block_x_14 ^ 8;
sha1_process_block_e = sha1_process_block_tm;
sha1_process_block_tm = x[8];
c += sha1_process_block_x_14 = sha1_process_block_tm;
b += sha1_process_block_x_15;
sha1_process_block_tm = x_0 ^ x[3];
sha1_process_block_a += sha1_process_block_tm;
sha1_process_block_tm = x[4] ^ x[15];
sha1_process_block_e +=
sha1_process_block_a + b ^ sha1_process_block_d +
sha1_process_block_tm;
sha1_process_block_tm = sha1_process_block_x_6 ^ x[15];
sha1_process_block_d +=
sha1_process_block_e >>
5 + (sha1_process_block_x_6 = sha1_process_block_tm);
sha1_process_block_ctx_0 += sha1_process_block_ctx_1 +=
sha1_process_block_ctx_2 += c;
sha1_process_block_ctx_3 += sha1_process_block_ctx->E +=
sha1_process_block_e;
}
}
we try to do this:
fusing pair [L=0] (200,199), base=31, hazards: (27,54), move_range: (54,54)
with the initial IR:
insn i200 in bb3 [ebb3] at point 102:
+---------------------------
| 200: [sp:DI+0x64]=x0:SI
| REG_DEAD x0:SI
+---------------------------
uses:
use of set r0:i37 (x0:SI)
use of phi node r31:a12 (sp:DI)
appears inside an address
defines:
set mem:i200
insn i198 in bb3 [ebb3] at point 104:
+---------------------------
| 198: [sp:DI+0x6c]=x2:SI
| REG_DEAD x2:SI
+---------------------------
uses:
use of set r2:i81 (x2:SI)
use of phi node r31:a12 (sp:DI)
appears inside an address
defines:
set mem:i198
used by insn i27 in bb3 [ebb3] at point 108
insn i54 in bb3 [ebb3] at point 106:
+--------------------------
| 54: x2:SI=x16:SI<<0x1
+--------------------------
uses:
SI use of set r16:i28 (x16:DI)
defines:
set r2:i54 (x2:SI)
used by insn i199 in bb3 [ebb3] at point 110
insn i27 in bb3 [ebb3] at point 108:
+--------------------------------------------
| 27: x0:DI=zero_extend([x1:DI+0x18])
| REG_EQUAL [const(`*.LANCHOR0'+0x18)]
+--------------------------------------------
uses:
use of set r1:i223 (x1:DI)
appears inside an address
use of set mem:i198
defines:
set r0:i27 (x0:DI)
live out from bb3 [ebb3] at point 114
used by phi node r0:a15 (x0:DI) in ebb6 at point 116
insn i199 in bb3 [ebb3] at point 110:
+---------------------------
| 199: [sp:DI+0x68]=x2:SI
| REG_DEAD x2:SI
+---------------------------
uses:
use of set r2:i54 (x2:SI)
use of phi node r31:a12 (sp:DI)
appears inside an address
defines:
set mem:i199
used by phi node mem:a15 in ebb6 at point 116
as it stands, after fusing that pair, we have:
insn i200 in bb3 [ebb3] at point 102:
+--------------------------
| 200: clobber [scratch]
+--------------------------
defines:
set mem:i200
insn i198 in bb3 [ebb3] at point 104:
+---------------------------
| 198: [sp:DI+0x6c]=x2:SI
| REG_DEAD x2:SI
+---------------------------
uses:
use of set r2:i81 (x2:SI)
use of phi node r31:a12 (sp:DI)
appears inside an address
defines:
set mem:i198
used by insn i27 in bb3 [ebb3] at point 108
insn i54 in bb3 [ebb3] at point 106:
+--------------------------
| 54: x2:SI=x16:SI<<0x1
+--------------------------
uses:
SI use of set r16:i28 (x16:DI)
defines:
set r2:i54 (x2:SI)
used by insn i244 in bb3 [ebb3] at point 107
insn i244 in bb3 [ebb3] at point 107:
+--------------------------------------------
| 244: [sp:DI+0x64]=unspec[x0:SI,x2:SI] 38
+--------------------------------------------
uses:
use of set r0:i37 (x0:SI)
use of set r2:i54 (x2:SI)
use of phi node r31:a12 (sp:DI)
appears inside an address
defines:
set mem:i244
insn i27 in bb3 [ebb3] at point 108:
+--------------------------------------------
| 27: x0:DI=zero_extend([x1:DI+0x18])
| REG_EQUAL [const(`*.LANCHOR0'+0x18)]
+--------------------------------------------
uses:
use of set r1:i223 (x1:DI)
appears inside an address
use of set mem:i198
defines:
set r0:i27 (x0:DI)
live out from bb3 [ebb3] at point 114
used by phi node r0:a15 (x0:DI) in ebb6 at point 116
insn i199 in bb3 [ebb3] at point 110:
+--------------------------
| 199: clobber [scratch]
+--------------------------
defines:
set mem:i199
used by phi node mem:a15 in ebb6 at point 116
The use problem is already visible here: i27 is consuming mem from i198,
but it should be consuming mem from our newly-inserted stp (i244).
The def problem is visible if we look in GDB:
(gdb) call debug (i2)
insn i199 in bb3 [ebb3] at point 110:
+--------------------------
| 199: clobber [scratch]
+--------------------------
defines:
set mem:i199
used by phi node mem:a15 in ebb6 at point 116
(gdb) call debug (i2->defs ()[0])
set mem:i199 in bb3 [ebb3] at point 110
used by phi node mem:a15 in ebb6 at point 116
(gdb) call debug (i2->defs ()[0]->prev_def ())
set mem:i198 in bb3 [ebb3] at point 104
used by insn i27 in bb3 [ebb3] at point 108
here the previous def should be our new stp (i244) instead of i198.
I have patches to fix both of these issues.
