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combine: Do not call simplify from inside change_zero_ext (PR78232)

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When combine splits a three-insn combination into two instructions it
can reuse i2dest for the temporary result of the first new instruction.
However all information it has in reg_stat about that register will be
stale.  This results in the simplify_gen_binary calls in change_zero_ext
using out-of-date information, which makes it think one of the ANDs
generated there always results in 0, and it doesn't get better from there.

This can also happen if a splitter in the MD uses nonzero_bits (for
example).  I tried to make the splitting code in combine save and restore
the i2dest reg_stat info, but that causes one of the acats tests to fail.

This whole reg_stat thing needs an overhaul, and/or we shouldn't reuse
i2dest for unrelated purposes when splitting.

This patch changes change_zero_ext to do the expected simplifications
itself and not call simplify_gen_*.


	PR rtl-optimization/78232
	* combine.c (try_combine): Add a big comment about why reusing i2dest
	is undesirable.
	(change_zero_ext): Do not call simplify_gen_binary, do the
	simplifications manually.

From-SVN: r242059
This commit is contained in:
Segher Boessenkool 2016-11-10 23:45:39 +01:00 • committed by Segher Boessenkool
parent 9490321264
commit 071af74db6
2 changed files with 30 additions and 9 deletions
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8
gcc/ChangeLog
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@ -1,3 +1,11 @@
2016-11-10 Segher Boessenkool <segher@kernel.crashing.org>
PR rtl-optimization/78232
* combine.c (try_combine): Add a big comment about why reusing i2dest
is undesirable.
(change_zero_ext): Do not call simplify_gen_binary, do the
simplifications manually.
2016-11-10 Michael Meissner <meissner@linux.vnet.ibm.com>
* config/rs6000/rs6000.c (rs6000_hard_regno_mode_ok): If ISA 3.0,

31
gcc/combine.c
View file

@ -3528,6 +3528,15 @@ try_combine (rtx_insn *i3, rtx_insn *i2, rtx_insn *i1, rtx_insn *i0,
{
machine_mode new_mode = GET_MODE (SET_DEST (newpat));
/* ??? Reusing i2dest without resetting the reg_stat entry for it
(temporarily, until we are committed to this instruction
combination) does not work: for example, any call to nonzero_bits
on the register (from a splitter in the MD file, for example)
will get the old information, which is invalid.
Since nowadays we can create registers during combine just fine,
we should just create a new one here, not reuse i2dest. */
/* First try to split using the original register as a
scratch register. */
parallel = gen_rtx_PARALLEL (VOIDmode,
@ -11133,8 +11142,10 @@ change_zero_ext (rtx pat)
if (BITS_BIG_ENDIAN)
start = GET_MODE_PRECISION (mode) - size - start;
x = simplify_gen_binary (LSHIFTRT, mode,
XEXP (x, 0), GEN_INT (start));
if (start)
x = gen_rtx_LSHIFTRT (mode, XEXP (x, 0), GEN_INT (start));
else
x = XEXP (x, 0);
}
else if (GET_CODE (x) == ZERO_EXTEND
&& SCALAR_INT_MODE_P (mode)
@ -11190,16 +11201,18 @@ change_zero_ext (rtx pat)
if (BITS_BIG_ENDIAN)
offset = reg_width - width - offset;
rtx x, y, z, w;
wide_int mask = wi::shifted_mask (offset, width, true, reg_width);
rtx x = gen_rtx_AND (mode, reg, immed_wide_int_const (mask, mode));
rtx y = simplify_gen_binary (ASHIFT, mode, SET_SRC (pat),
GEN_INT (offset));
wide_int mask2 = wi::shifted_mask (offset, width, false, reg_width);
y = simplify_gen_binary (AND, mode, y,
immed_wide_int_const (mask2, mode));
rtx z = simplify_gen_binary (IOR, mode, x, y);
x = gen_rtx_AND (mode, reg, immed_wide_int_const (mask, mode));
if (offset)
y = gen_rtx_ASHIFT (mode, SET_SRC (pat), GEN_INT (offset));
else
y = SET_SRC (pat);
z = gen_rtx_AND (mode, y, immed_wide_int_const (mask2, mode));
w = gen_rtx_IOR (mode, x, z);
SUBST (SET_DEST (pat), reg);
SUBST (SET_SRC (pat), z);
SUBST (SET_SRC (pat), w);
changed = true;
}