xref: /freebsd-9.3-release/contrib/gcc/config/s390/s390-modes.def

/* Definitions of target machine for GNU compiler, for IBM S/390
   Copyright (C) 2002, 2003, 2004, 2005 Free Software Foundation, Inc.
   Contributed by Hartmut Penner (hpenner@de.ibm.com) and
                  Ulrich Weigand (uweigand@de.ibm.com).

This file is part of GCC.

GCC is free software; you can redistribute it and/or modify it under
the terms of the GNU General Public License as published by the Free
Software Foundation; either version 2, or (at your option) any later
version.

GCC is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
for more details.

You should have received a copy of the GNU General Public License
along with GCC; see the file COPYING.  If not, write to the Free
Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA
02110-1301, USA.  */

/* 256-bit integer mode is needed for STACK_SAVEAREA_MODE.  */
INT_MODE (OI, 32);

/* Define TFmode to work around reload problem PR 20927.  */
FLOAT_MODE (TF, 16, ieee_quad_format);

/* Add any extra modes needed to represent the condition code.  */

/*

Condition Codes

Check for zero

CCZ:  EQ          NE           NE          NE
CCZ1: EQ          NE                                  (CS)

Unsigned compares

CCU:  EQ          LTU          GTU         NE         (CLG/R, CL/R/Y, CLM/Y, CLI/Y)
CCUR: EQ          GTU          LTU         NE         (CLGF/R)

Signed compares

CCS:  EQ          LT           GT          UNORDERED  (LTGFR, LTGR, LTR, ICM/Y,
                                                       LTDBR, LTDR, LTEBR, LTER,
                                                       CG/R, C/R/Y, CGHI, CHI, 
                                                       CDB/R, CD/R, CEB/R, CE/R, 
                                                       ADB/R, AEB/R, SDB/R, SEB/R,
                                                       SRAG, SRA, SRDA)
CCSR: EQ          GT           LT          UNORDERED  (CGF/R, CH/Y)

Condition codes resulting from add with overflow

CCA:  EQ          LT           GT          Overflow
CCAP: EQ          LT           GT          LT         (AGHI, AHI)
CCAN: EQ          LT           GT          GT         (AGHI, AHI)

Condition codes of unsigned adds and subs

CCL:  EQ          NE           EQ          NE         (ALGF/R, ALG/R, AL/R/Y,
                                                       ALCG/R, ALC/R, 
                                                       SLGF/R, SLG/R, SL/R/Y,
                                                       SLBG/R, SLB/R)
CCL1: GEU         GEU          LTU         LTU        (ALG/R, AL/R/Y)
CCL2: GTU         GTU          LEU         LEU        (SLG/R, SL/R/Y)
CCL3: EQ          LTU          EQ          GTU        (SLG/R, SL/R/Y)

Test under mask checks

CCT:  EQ          NE           NE          NE         (ICM/Y, TML, CG/R, CGHI, 
                                                       C/R/Y, CHI, NG/R, N/R/Y,
                                                       OG/R, O/R/Y, XG/R, X/R/Y)
CCT1: NE          EQ           NE          NE         (TMH, TML)
CCT2: NE          NE           EQ          NE         (TMH, TML)
CCT3: NE          NE           NE          EQ         (TMH, TML)

CCA and CCT modes are request only modes. These modes are never returned by 
s390_select_cc_mode. They are only intended to match other modes.

Requested mode            -> Destination CC register mode

CCS, CCU, CCT, CCSR, CCUR -> CCZ
CCA                       -> CCAP, CCAN


*** Comments ***

CCAP, CCAN

The CC obtained from add instruction usually can't be used for comparisons 
because its coupling with overflow flag. In case of an overflow the
less than/greater than data are lost. Nevertheless a comparison can be done
whenever immediate values are involved because they are known at compile time.
If you know whether the used constant is positive or negative you can predict 
the sign of the result even in case of an overflow.


CCT, CCT1, CCT2, CCT3

If bits of an integer masked with an AND instruction are checked, the test under
mask instructions turn out to be very handy for a set of special cases.
The simple cases are checks whether all masked bits are zero or ones:

  int a; 
  if ((a & (16 + 128)) == 0)          -> CCT/CCZ
  if ((a & (16 + 128)) == 16 + 128)   -> CCT3

Using two extra modes makes it possible to do complete checks on two bits of an
integer (This is possible on register operands only. TM does not provide the
information necessary for CCT1 and CCT2 modes.):

  int a;
  if ((a & (16 + 128)) == 16)         -> CCT1
  if ((a & (16 + 128)) == 128)        -> CCT2


CCSR, CCUR

There are several instructions comparing 32 bit with 64 bit unsigned/signed
values. Such instructions can be considered to have a builtin zero/sign_extend.
The problem is that in the RTL (to be canonical) the zero/sign extended operand 
has to be the first one but the machine instructions like it the other way 
around. The following both modes can be considered as CCS and CCU modes with 
exchanged operands.


CCL1, CCL2

These modes represent the result of overflow checks. 

if (a + b < a) -> CCL1 state of the carry bit   (CC2 | CC3)
if (a - b > a) -> CCL2 state of the borrow bit  (CC0 | CC1)

They are used when multi word numbers are computed dealing one SImode part after
another or whenever manual overflow checks like the examples above are
compiled.


CCL3

A logical subtract instruction sets the borrow bit in case of an overflow.
The resulting condition code of those instructions is represented by the
CCL3 mode. Together with the CCU mode this mode is used for jumpless 
implementations of several if-constructs - see s390_expand_addcc for more
details.

CCZ1

The compare and swap instructions sets the condition code to 0/1 if the
operands were equal/unequal. The CCZ1 mode ensures the result can be
effectively placed into a register.

*/   


CC_MODE (CCZ);
CC_MODE (CCZ1);
CC_MODE (CCA);
CC_MODE (CCAP);
CC_MODE (CCAN);
CC_MODE (CCL);
CC_MODE (CCL1);
CC_MODE (CCL2);
CC_MODE (CCL3);
CC_MODE (CCU);
CC_MODE (CCUR);
CC_MODE (CCS);
CC_MODE (CCSR);
CC_MODE (CCT);
CC_MODE (CCT1);
CC_MODE (CCT2);
CC_MODE (CCT3);