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Re: [patch] MIPS/gcc: Revert removal of DImode shifts for 32-bit targets

To: Richard Sandiford <rsandifo@redhat.com>
Subject: Re: [patch] MIPS/gcc: Revert removal of DImode shifts for 32-bit targets
From: Nigel Stephens <nigel@mips.com>
Date: Tue, 03 Aug 2004 10:54:39 +0100
Cc: "Maciej W. Rozycki" <macro@linux-mips.org>, Ralf Baechle <ralf@linux-mips.org>, Richard Henderson <rth@redhat.com>, gcc-patches@gcc.gnu.org, linux-mips@linux-mips.org
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Richard Sandiford wrote:

I think we should only use define_expands if there's a truly
MIPS-specific feature in the expansion (as there is in the block
move stuff, for example, where we use left/right loads and stores).


Fair enough.

Now obviously I'm only guessing what insn sequence you're using,

OK, the simplest thing is for me to attach the define_insns. See below.

Note that there is one slightly controversial aspect of these sequences, which is that they don't truncate the shift count, so a shift outside of the range 0 to 63 will generate an "unusual" result. This didn't cause any regression failures, and I believe that this is strictly speaking acceptable for C, since a shift is undefined outside of this range - but it could cause some "buggy" code to break. It wouldn't be hard to add an extra mask with 0x3f if people were nervous about this - it's just that I didn't have enough spare temp registers within the constraints of the existing DImode patterns.

---- cut here ---

;; XXX Would be better done using define_expand, so it can be scheduled
;; XXX Note won't handle a shift count outside the range 0 - 63
(define_insn "ashldi3_internal_movc"
 [(set (match_operand:DI 0 "register_operand" "=&d")
   (ashift:DI (match_operand:DI 1 "register_operand" "d")
          (match_operand:SI 2 "register_operand" "d")))
  (clobber (match_operand:SI 3 "register_operand" "=&d"))]
 "!TARGET_64BIT && !TARGET_DEBUG_G_MODE && !TARGET_MIPS16
  && ISA_HAS_CONDMOVE"
 "subu\t%3,%.,%2\;\
sll\t%M0,%M1,%2\;\
srl\t%3,%L1,%3\;\
sll\t%L0,%L1,%2\;\
movz\t%3,%.,%2\;\
or\t%M0,%M0,%3\;\
and\t%3,%2,32\;\
movn\t%M0,%L0,%3\;\
movn\t%L0,%.,%3"
 [(set_attr "type"    "darith")
  (set_attr "mode"    "DI")
  (set_attr "length"    "36")])

;; Same length as before, but avoids branches
;; XXX Note won't handle a shift count outside the range 0 - 63
(define_insn "ashrdi3_internal_movc"
 [(set (match_operand:DI 0 "register_operand" "=&d")
   (ashiftrt:DI (match_operand:DI 1 "register_operand" "d")
            (match_operand:SI 2 "register_operand" "d")))
  (clobber (match_operand:SI 3 "register_operand" "=&d"))]
 "!TARGET_64BIT && !TARGET_DEBUG_G_MODE && !TARGET_MIPS16
  && ISA_HAS_CONDMOVE"
 "subu\t%3,%.,%2\;\
srl\t%L0,%L1,%2\;\
sll\t%3,%M1,%3\;\
sra\t%M0,%M1,%2\;\
movz\t%3,%.,%2\;\
or\t%L0,%L0,%3\;\
and\t%3,%2,32\;\
movn\t%L0,%M0,%3\;\
movn\t%M0,%.,%3\;\
movn\t%3,%L0,%3\;\
sra\t%3,%3,31\;\
or\t%M0,%M0,%3"
 [(set_attr "type"    "darith")
  (set_attr "mode"    "DI")
  (set_attr "length"    "48")])

;;; XXX Note won't handle a shift count outside the range 0 - 63
(define_insn "lshrdi3_internal_movc"
 [(set (match_operand:DI 0 "register_operand" "=&d")
   (lshiftrt:DI (match_operand:DI 1 "register_operand" "d")
            (match_operand:SI 2 "register_operand" "d")))
  (clobber (match_operand:SI 3 "register_operand" "=&d"))]
 "!TARGET_64BIT && !TARGET_DEBUG_G_MODE && !TARGET_MIPS16
  && ISA_HAS_CONDMOVE"
 "subu\t%3,%.,%2\;\
srl\t%L0,%L1,%2\;\
sll\t%3,%M1,%3\;\
srl\t%M0,%M1,%2\;\
movz\t%3,%.,%2\;\
or\t%L0,%L0,%3\;\
and\t%3,%2,32\;\
movn\t%L0,%M0,%3\;\
movn\t%M0,%.,%3"
 [(set_attr "type"    "darith")
  (set_attr "mode"    "DI")
  (set_attr "length"    "36")])


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