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Clarify documentation of RTL code COMPARE
- To: gcc-patches at gcc dot gnu dot org
- Subject: Clarify documentation of RTL code COMPARE
- From: kenner at vlsi1 dot ultra dot nyu dot edu (Richard Kenner)
- Date: Tue, 20 Mar 01 20:17:26 EST
Tue Mar 20 20:15:06 2001 Richard Kenner <kenner@vlsi1.ultra.nyu.edu>
* rtl.texi (COMPARE): Clarify documentation and reference section
on comparisons.
*** rtl.texi 2001/02/02 06:11:26 1.35
--- rtl.texi 2001/03/21 00:55:32
*************** infinite precision.
*** 1413,1425 ****
Of course, machines can't really subtract with infinite precision.
! However, they can pretend to do so when only the sign of the
! result will be used, which is the case when the result is stored
! in the condition code. And that is the only way this kind of expression
! may validly be used: as a value to be stored in the condition codes.
! The mode @var{m} is not related to the modes of @var{x} and @var{y},
! but instead is the mode of the condition code value. If @code{(cc0)}
! is used, it is @code{VOIDmode}. Otherwise it is some mode in class
! @code{MODE_CC}, often @code{CCmode}. @xref{Condition Code}.
Normally, @var{x} and @var{y} must have the same mode. Otherwise,
--- 1413,1431 ----
Of course, machines can't really subtract with infinite precision.
! However, they can pretend to do so when only the sign of the result will
! be used, which is the case when the result is stored in the condition
! code. And that is the @emph{only} way this kind of expression may
! validly be used: as a value to be stored in the condition codes, either
! @code{(cc0)} or a register. @xref{Comparisons}.
! The mode @var{m} is not related to the modes of @var{x} and @var{y}, but
! instead is the mode of the condition code value. If @code{(cc0)} is
! used, it is @code{VOIDmode}. Otherwise it is some mode in class
! @code{MODE_CC}, often @code{CCmode}. @xref{Condition Code}. If @var{m}
! is @code{VOIDmode} or @code{CCmode}, the operation returns sufficient
! information (in an unspecified format) so that any comparison operator
! can be applied to the result of the @code{COMPARE} operation. For other
! modes in class @code{MODE_CC}, the operation only returns a subset of
! this information.
Normally, @var{x} and @var{y} must have the same mode. Otherwise,