* [doc] deprecate the old pipeline description
@ 2004-07-09 16:55 Steven Bosscher
2004-07-09 21:56 ` Richard Henderson
0 siblings, 1 reply; 2+ messages in thread
From: Steven Bosscher @ 2004-07-09 16:55 UTC (permalink / raw)
To: gcc-patches, gcc
Nobody has objected, so I guess we can go ahead and deprecate the
old pipeline description. Attached is a patch for the internals
manual. Should it be mentioned elsewhere too?
Gr.
Steven
* md.texi (Processor pipeline description): Mention that the old
pipeline description is deprecated.
Index: doc/md.texi
===================================================================
RCS file: /cvs/gcc/gcc/gcc/doc/md.texi,v
retrieving revision 1.104
diff -c -3 -p -r1.104 md.texi
*** doc/md.texi 8 Jul 2004 03:40:34 -0000 1.104
--- doc/md.texi 9 Jul 2004 15:48:29 -0000
*************** instruction scheduler has to have an ade
*** 5536,5545 ****
processor parallelism (or @dfn{pipeline description}). Currently GCC
provides two alternative ways to describe processor parallelism,
both described below. The first method is outlined in the next section;
! it was once the only method provided by GCC, and thus is used in a number
! of exiting ports. The second, and preferred method, specifies functional
! unit reservations for groups of instructions with the aid of @dfn{regular
! expressions}. This is called the @dfn{automaton based description}.
The GCC instruction scheduler uses a @dfn{pipeline hazard recognizer} to
figure out the possibility of the instruction issue by the processor
--- 5536,5550 ----
processor parallelism (or @dfn{pipeline description}). Currently GCC
provides two alternative ways to describe processor parallelism,
both described below. The first method is outlined in the next section;
! it specifies functional unit reservations for groups of instructions
! with the aid of @dfn{regular expressions}. This is called the
! @dfn{automaton based description}. The second method is called the
! @dfn{old pipeline description}. This method specifies usage of
! function units for classes of insns. This description is not as
! powerful or accurate as the automaton based description, because it
! is impossible to model instructions that use more than one function
! unit. The second method is deprecated; new ports should use the
! automaton based description.
The GCC instruction scheduler uses a @dfn{pipeline hazard recognizer} to
figure out the possibility of the instruction issue by the processor
*************** generated from the old description. Fur
*** 5552,5571 ****
on processor complexity. The instruction issue is possible if there is
a transition from one automaton state to another one.
- You can use either model to describe processor pipeline
- characteristics or even mix them. You could use the old description
- for some processor submodels and the @acronym{DFA}-based one for other
- processor submodels.
-
- In general, using the automaton based description is preferred. Its
- model is richer and makes it possible to more accurately describe
- pipeline characteristics of processors, which results in improved
- code quality (although sometimes only marginally). It will also be
- used as an infrastructure to implement sophisticated and practical
- instruction scheduling which will try many instruction sequences to
- choose the best one.
-
-
@menu
* Old pipeline description:: Specifying information for insn scheduling.
* Automaton pipeline description:: Describing insn pipeline characteristics.
--- 5557,5562 ----
*************** choose the best one.
*** 5579,5584 ****
--- 5570,5577 ----
@cindex old pipeline description
@cindex function units, for scheduling
+ @emph{Note:}The old pipeline description is deprecated.
+
On most @acronym{RISC} machines, there are instructions whose results
are not available for a specific number of cycles. Common cases are
instructions that load data from memory. On many machines, a pipeline
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