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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/113059] [14 regression] fftw fails tests for -O3 -m32
 -march=znver2 since r14-6210-ge44ed92dbbe9d4
Date: Tue, 30 Jan 2024 11:17:41 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D113059

--- Comment #22 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
BTW, I have quickly looked at REG_UNUSED notes on insn-recog.cc (as a rando=
mly
picked large GCC object).  Ignoring REG_UNUSED notes for flags register (wh=
ich
are extremely common in lots of passes), seems we have just a few such notes
before RA and probably combiner kills them?
insn-recog.cc.292r.cse2:        (expr_list:REG_UNUSED (reg:SI 207)
insn-recog.cc.293r.dse1:        (expr_list:REG_UNUSED (reg:SI 207)
insn-recog.cc.294r.fwprop2:        (expr_list:REG_UNUSED (reg:SI 207)
insn-recog.cc.296r.init-regs:        (expr_list:REG_UNUSED (reg:SI 207)
insn-recog.cc.297r.ud_dce:        (expr_list:REG_UNUSED (reg:SI 207)
insn-recog.cc.298r.combine:      REG_UNUSED r207:SI
insn-recog.cc.298r.combine:      REG_UNUSED r207:SI
Then I see tons of REG_UNUSED notes for non-flags in IRA dump (all new), but
they don't appear after it, so most likely LRA removes them.  Even the flags
related REG_UNUSED don't appear in *.reload dump (except some details
comments), nor *.postreload etc.
And (note, this isn't a build with -mavx*, so no vzeroupper), they reappear
only in dse2 dump and keep appearing from that point onwards.
Similarly REG_DEAD notes don't appear in the IL between *.reload and
*.pro_and_epilogue inclusive.
Seems LRA does this in update_inc_notes, reload did that in reload function.

So, maybe safer than the above patch would be simply do that too in vzeroup=
per
pass (I guess we don't need to update the REG_INC notes).
Let me write another patch.=