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From: Vineet Gupta <vineetg@rivosinc.com>
To: Jakub Jelinek <jakub@redhat.com>
Cc: gcc@gcc.gnu.org, Michael Collison <collison@rivosinc.com>,
	Jeff Law <jeffreyalaw@gmail.com>
Subject: query about commit 666fdc46bc8489 ("RISC-V: Fix bad insn splits with paradoxical subregs")
Date: Fri, 4 Nov 2022 15:59:58 -0700	[thread overview]
Message-ID: <23ac9d02-c687-7680-493b-8ace1558a4cb@rivosinc.com> (raw)

Hi Jakub,

I had a question about the aforementioned commit in RV backend.

(define_split
   [(set (match_operand:GPR 0 "register_operand")
	(and:GPR (match_operand:GPR 1 "register_operand")
                (match_operand:GPR 2 "p2m1_shift_operand")))
+   (clobber (match_operand:GPR 3 "register_operand"))]
   ""
-  [(set (match_dup 0)
+  [(set (match_dup 3)
        (ashift:GPR (match_dup 1) (match_dup 2)))

Is there something specific to this split which warrants this or so any 
split patterns involving shifts have this to avoid the shifting by more 
than SUBREG_REG problem.

Also could you please explain where the clobber itself is allocated ?

This came up when discussing the solution to PR/106602 [1]


Thx,
-Vineet

[1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106602

             reply	other threads:[~2022-11-04 23:00 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-11-04 22:59 Vineet Gupta [this message]
2022-11-04 23:13 ` Jeff Law
2022-11-04 23:38   ` Vineet Gupta
2022-11-04 23:47     ` Jeff Law

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