77 lines
2.5 KiB
Diff
77 lines
2.5 KiB
Diff
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Based on Richi's patch:
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<https://gcc.gnu.org/pipermail/gcc-patches/2024-April/648725.html>
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~~
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The following avoids re-walking and re-combining the instructions
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between i2 and i3 when the pattern of i2 doesn't change.
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Bootstrap and regtest running ontop of a reversal of
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r14-9692-g839bc42772ba7a.
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It brings down memory use from 9GB to 400MB and compile-time from
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80s to 3.5s. r14-9692-g839bc42772ba7a does better in both metrics
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but has shown code generation regressions across architectures.
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PR rtl-optimization/101523
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* combine.cc (try_combine): When the pattern of i2 doesn't
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change do not re-start combining at i2 or an earlier insn which
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had links or notes added.
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~~
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But, since the patch affects code generation (for instance,
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libstdc++-v3/src/c++17/floating_from_chars.o), we limit the bailing out
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only when I2 hasn't been changed 1000x. I've measured how many times
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at most is I2 unchanged during a bootstrap + regtest.
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x86: 134
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aarch64: 736 (gimple-match-1.cc)
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s390x: 635 (gimple-match-*)
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ppc64le: 620 (gimple-match-*)
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while certain pathological testcases trigger it more than 10,000 times.
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With the limit in place this patch doesn't affect common code.
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--- a/gcc/combine.cc
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+++ b/gcc/combine.cc
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@@ -92,6 +92,11 @@ along with GCC; see the file COPYING3. If not see
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#include "function-abi.h"
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#include "rtlanal.h"
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+/* Number of times I2 didn't change in try_combine. Used to prevent a
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+ combinatorial explosion. */
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+
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+static int combine_i2_unchanged;
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+
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/* Number of attempts to combine instructions in this function. */
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static int combine_attempts;
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@@ -1127,6 +1132,7 @@ combine_instructions (rtx_insn *f, unsigned int nregs)
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return false;
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combine_attempts = 0;
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+ combine_i2_unchanged = 0;
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combine_merges = 0;
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combine_extras = 0;
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combine_successes = 0;
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@@ -4196,6 +4201,10 @@ 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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+ bool i2_i2_unchanged = false;
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+ if (rtx_equal_p (newi2pat, PATTERN (i2)))
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+ i2_i2_unchanged = true;
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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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@@ -4762,6 +4771,13 @@ try_combine (rtx_insn *i3, rtx_insn *i2, rtx_insn *i1, rtx_insn *i0,
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combine_successes++;
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undo_commit ();
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+ if (i2_i2_unchanged)
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+ {
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+ if (combine_i2_unchanged == 1000)
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+ return i3;
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+ ++combine_i2_unchanged;
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+ }
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+
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rtx_insn *ret = newi2pat ? i2 : i3;
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if (added_links_insn && DF_INSN_LUID (added_links_insn) < DF_INSN_LUID (ret))
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ret = added_links_insn;
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