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combine: Update links correctly for new I2 (PR84169)

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If there is a LOG_LINK between two insns, this means those two insns
can be combined, as far as dataflow is concerned.  There never should
be a LOG_LINK between two unrelated insns.  If there is one, combine
will try to combine the insns without doing all the needed checks if
the earlier destination is used before the later insn, etc.

Unfortunately we do not update the LOG_LINKs correctly in some cases.
This patch fixes at least some of those cases.


	PR rtl-optimization/84169
	* combine.c (try_combine): New variable split_i2i3.  Set it to true if
	we generated a parallel as new i3 and we split that to new i2 and i3
	instructions.  Handle split_i2i3 similar to swap_i2i3: scan the
	LOG_LINKs of i3 to see which of those need to link to i2 now.  Link
	those to i2, not i1.  Partially rewrite this scan code.

gcc/testsuite/
	PR rtl-optimization/84169
	* gcc.c-torture/execute/pr84169.c: New.

From-SVN: r257644
This commit is contained in:
Segher Boessenkool 2018-02-13 23:12:55 +01:00 committed by Segher Boessenkool
parent b7a6b85f8a
commit ba95aa2096
4 changed files with 69 additions and 25 deletions
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9
gcc/ChangeLog
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@ -1,3 +1,12 @@
2018-02-13 Segher Boessenkool <segher@kernel.crashing.org>
PR rtl-optimization/84169
* combine.c (try_combine): New variable split_i2i3. Set it to true if
we generated a parallel as new i3 and we split that to new i2 and i3
instructions. Handle split_i2i3 similar to swap_i2i3: scan the
LOG_LINKs of i3 to see which of those need to link to i2 now. Link
those to i2, not i1. Partially rewrite this scan code.
2018-02-13 Jakub Jelinek <jakub@redhat.com>
PR c/82210

55
gcc/combine.c
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@ -2665,6 +2665,7 @@ try_combine (rtx_insn *i3, rtx_insn *i2, rtx_insn *i1, rtx_insn *i0,
/* Notes that I1, I2 or I3 is a MULT operation. */
int have_mult = 0;
int swap_i2i3 = 0;
int split_i2i3 = 0;
int changed_i3_dest = 0;
int maxreg;
@ -4091,6 +4092,9 @@ try_combine (rtx_insn *i3, rtx_insn *i2, rtx_insn *i1, rtx_insn *i0,
}
insn_code_number = recog_for_combine (&newpat, i3, &new_i3_notes);
if (insn_code_number >= 0)
split_i2i3 = 1;
}
}
@ -4258,44 +4262,45 @@ try_combine (rtx_insn *i3, rtx_insn *i2, rtx_insn *i1, rtx_insn *i0,
if (swap_i2i3)
{
rtx_insn *insn;
struct insn_link *link;
rtx ni2dest;
/* I3 now uses what used to be its destination and which is now
I2's destination. This requires us to do a few adjustments. */
PATTERN (i3) = newpat;
adjust_for_new_dest (i3);
}
/* We need a LOG_LINK from I3 to I2. But we used to have one,
so we still will.
if (swap_i2i3 || split_i2i3)
{
/* We might need a LOG_LINK from I3 to I2. But then we used to
have one, so we still will.
However, some later insn might be using I2's dest and have
a LOG_LINK pointing at I3. We must remove this link.
The simplest way to remove the link is to point it at I1,
which we know will be a NOTE. */
a LOG_LINK pointing at I3. We should change it to point at
I2 instead. */
/* newi2pat is usually a SET here; however, recog_for_combine might
have added some clobbers. */
if (GET_CODE (newi2pat) == PARALLEL)
ni2dest = SET_DEST (XVECEXP (newi2pat, 0, 0));
else
ni2dest = SET_DEST (newi2pat);
rtx x = newi2pat;
if (GET_CODE (x) == PARALLEL)
x = XVECEXP (newi2pat, 0, 0);
for (insn = NEXT_INSN (i3);
insn && (this_basic_block->next_bb == EXIT_BLOCK_PTR_FOR_FN (cfun)
|| insn != BB_HEAD (this_basic_block->next_bb));
unsigned int regno = REGNO (SET_DEST (x));
bool done = false;
for (rtx_insn *insn = NEXT_INSN (i3);
!done
&& insn
&& NONDEBUG_INSN_P (insn)
&& BLOCK_FOR_INSN (insn) == this_basic_block;
insn = NEXT_INSN (insn))
{
if (NONDEBUG_INSN_P (insn)
&& reg_referenced_p (ni2dest, PATTERN (insn)))
{
FOR_EACH_LOG_LINK (link, insn)
if (link->insn == i3)
link->insn = i1;
break;
}
struct insn_link *link;
FOR_EACH_LOG_LINK (link, insn)
if (link->insn == i3 && link->regno == regno)
{
link->insn = i2;
done = true;
break;
}
}
}

5
gcc/testsuite/ChangeLog
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@ -1,3 +1,8 @@
2018-02-13 Segher Boessenkool <segher@kernel.crashing.org>
PR rtl-optimization/84169
* gcc.c-torture/execute/pr84169.c: New.
2018-02-13 Peter Bergner <bergner@vnet.ibm.com>
PR target/84370

25
gcc/testsuite/gcc.c-torture/execute/pr84169.c Normal file
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@ -0,0 +1,25 @@
/* PR rtl-optimization/84169 */
#ifdef __SIZEOF_INT128__
typedef unsigned __int128 T;
#else
typedef unsigned long long T;
#endif
T b;
static __attribute__ ((noipa)) T
foo (T c, T d, T e, T f, T g, T h)
{
__builtin_mul_overflow ((unsigned char) h, -16, &h);
return b + h;
}
int
main ()
{
T x = foo (0, 0, 0, 0, 0, 4);
if (x != -64)
__builtin_abort ();
return 0;
}