49 lines
1.6 KiB
Diff
49 lines
1.6 KiB
Diff
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From 839bc42772ba7af66af3bd16efed4a69511312ae Mon Sep 17 00:00:00 2001
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From: Segher Boessenkool <segher@kernel.crashing.org>
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Date: Wed, 27 Mar 2024 14:09:52 +0000
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Subject: [PATCH] combine: Don't combine if I2 does not change
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To: gcc-patches@gcc.gnu.org
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In some cases combine will "combine" an I2 and I3, but end up putting
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exactly the same thing back as I2 as was there before. This is never
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progress, so we shouldn't do it, it will lead to oscillating behaviour
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and the like.
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If we want to canonicalise things, that's fine, but this is not the
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way to do it.
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2024-03-27 Segher Boessenkool <segher@kernel.crashing.org>
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PR rtl-optimization/101523
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* combine.cc (try_combine): Don't do a 2-insn combination if
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it does not in fact change I2.
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---
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gcc/combine.cc | 11 +++++++++++
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1 file changed, 11 insertions(+)
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diff --git a/gcc/combine.cc b/gcc/combine.cc
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index a4479f8d836..745391016d0 100644
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--- a/gcc/combine.cc
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+++ b/gcc/combine.cc
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@@ -4186,6 +4186,17 @@ try_combine (rtx_insn *i3, rtx_insn *i2, rtx_insn *i1, rtx_insn *i0,
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adjust_for_new_dest (i3);
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}
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+ /* If I2 didn't change, this is not a combination (but a simplification or
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+ canonicalisation with context), which should not be done here. Doing
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+ it here explodes the algorithm. Don't. */
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+ if (rtx_equal_p (newi2pat, PATTERN (i2)))
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+ {
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+ if (dump_file)
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+ fprintf (dump_file, "i2 didn't change, not doing this\n");
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+ undo_all ();
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+ return 0;
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+ }
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+
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/* We now know that we can do this combination. Merge the insns and
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update the status of registers and LOG_LINKS. */
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--
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2.35.3
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