From: Roger Sayle <roger@eyesopen.com>
Date: Wed, 19 May 2004 13:54:15 +0000 (+0000)
Subject: tm.texi (TARGET_RTX_COSTS): Document that instruction costs should be based on code... 
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=31a52b868a209f0c8f3ade10a91148664526dc9b;p=gcc.git

tm.texi (TARGET_RTX_COSTS): Document that instruction costs should be based on code size when...


	* doc/tm.texi (TARGET_RTX_COSTS): Document that instruction
	costs should be based on code size when optimizing for size.

From-SVN: r82025
---

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 3b616152160..ca2069d13fa 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,8 @@
+2004-05-19  Roger Sayle  <roger@eyesopen.com>
+
+	* doc/tm.texi (TARGET_RTX_COSTS): Document that instruction
+	costs should be based on code size when optimizing for size.
+
 2004-05-19  Paolo Bonzini  <bonzini@gnu.org>
 
 	* fold-const.c: Remove non-printable character 160.
diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi
index 43543a81103..67f4b7608a4 100644
--- a/gcc/doc/tm.texi
+++ b/gcc/doc/tm.texi
@@ -5456,7 +5456,13 @@ instructions.
 
 On entry to the hook, @code{*@var{total}} contains a default estimate
 for the cost of the expression.  The hook should modify this value as
-necessary.
+necessary.  Traditionally, the default costs are @code{COSTS_N_INSNS (5)}
+for multiplications, @code{COSTS_N_INSNS (7)} for division and modulus
+operations, and @code{COSTS_N_INSNS (1)} for all other operations.
+
+When optimizing for code size, i.e@. when @code{optimize_size} is
+non-zero, this target hook should be used to estimate the relative
+size cost of an expression, again relative to @code{COSTS_N_INSNS}.
 
 The hook returns true when all subexpressions of @var{x} have been
 processed, and false when @code{rtx_cost} should recurse.