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From: "ubizjak at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/114591] [12/13/14 Regression] register allocators
 introduce an extra load operation since gcc-12
Date: Wed, 10 Apr 2024 08:47:25 +0000
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X-Bugzilla-Type: changed
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X-Bugzilla-Product: gcc
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X-Bugzilla-Version: 13.2.0
X-Bugzilla-Keywords: missed-optimization, ra
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D114591

--- Comment #8 from Uro=C5=A1 Bizjak <ubizjak at gmail dot com> ---
BTW: The reason for the original change:

 (define_insn "*movhi_internal"
-  [(set (match_operand:HI 0 "nonimmediate_operand" "=3Dr,r ,r ,m ,*k,*k
,*r,*m,*k,?r,?v,*v,*v,*m")
-       (match_operand:HI 1 "general_operand"      "r
,rn,rm,rn,*r,*km,*k,*k,CBC,v, r, v, m, v"))]
+  [(set (match_operand:HI 0 "nonimmediate_operand"
+    "=3Dr,r,r,m ,*k,*k ,r ,m ,*k ,?r,?*v,*v,*v,*v,m")
+       (match_operand:HI 1 "general_operand"
+    "r ,n,m,rn,r ,*km,*k,*k,CBC,*v,r  ,C ,*v,m ,*v"))]

was that (r,r) overrides (r,rn) and (r,rm), so the later two can be changed
(without introducing any side effect) to (r,n) and (r,m), since (reg,reg) is
always matched by the (r,r) constraint. The different treatment of the chan=
ged
later two patterns is confusing at least.=