From 7dba8395e27f52d22aa11ff2fc147858e34f2a9d Mon Sep 17 00:00:00 2001
From: Richard Henderson <rth@redhat.com>
Date: Wed, 5 Feb 2003 14:37:54 -0800
Subject: defaults.h (CLZ_DEFINED_VALUE_AT_ZERO): New.

        * defaults.h (CLZ_DEFINED_VALUE_AT_ZERO): New.
        (CTZ_DEFINED_VALUE_AT_ZERO): New.
        * doc/rtl.texi, doc/tm.texi: Document them.

        * combine.c (nonzero_bits) [CLZ, CTZ]: Handle the definedness
        of the value at zero properly.
        * fold-const.c (tree_expr_nonnegative_p): Likewise.
        * simplify-rtx.c (simplify_unary_operation): Likewise.

        * config/alpha/alpha.h (CLZ_DEFINED_VALUE_AT_ZERO): New.
        (CTZ_DEFINED_VALUE_AT_ZERO): New.

        * config/arm/arm.c (TARGET_INIT_BUILTINS): Remove.
        (TARGET_EXPAND_BUILTIN): Remove.
        (def_builtin, arm_init_builtins, arm_expand_builtin): Remove.
        * config/arm/arm.h (CLZ_DEFINED_VALUE_AT_ZERO): New.
        (enum arm_builtins): Remove.
        * config/arm/arm.md (UNSPEC_CLZ): Remove.
        (clzsi2): Rename from clz; use clz instead of unspec.
        (ctzsi2): New.
        * config/arm/arm-protos.h: Update.

From-SVN: r62453
---
 gcc/doc/rtl.texi |  6 ++++--
 gcc/doc/tm.texi  | 19 +++++++++++++++++++
 2 files changed, 23 insertions(+), 2 deletions(-)

(limited to 'gcc/doc')

diff --git a/gcc/doc/rtl.texi b/gcc/doc/rtl.texi
index 1698517..7e696fa 100644
--- a/gcc/doc/rtl.texi
+++ b/gcc/doc/rtl.texi
@@ -1850,7 +1850,8 @@ valid.
 @item (clz:@var{m} @var{x})
 Represents the number of leading 0-bits in @var{x}, represented as an
 integer of mode @var{m}, starting at the most significant bit position.
-If @var{x} is zero, the value is undefined.  Note that this is one of
+If @var{x} is zero, the value is determined by
+@code{CLZ_DEFINED_VALUE_AT_ZERO}.  Note that this is one of
 the few expressions that is not invariant under widening.  The mode of
 @var{x} will usually be an integer mode.
 
@@ -1858,7 +1859,8 @@ the few expressions that is not invariant under widening.  The mode of
 @item (ctz:@var{m} @var{x})
 Represents the number of trailing 0-bits in @var{x}, represented as an
 integer of mode @var{m}, starting at the least significant bit position.
-If @var{x} is zero, the value is undefined.  Except for this case,
+If @var{x} is zero, the value is determined by
+@code{CTZ_DEFINED_VALUE_AT_ZERO}.  Except for this case,
 @code{ctz(x)} is equivalent to @code{ffs(@var{x}) - 1}.  The mode of
 @var{x} will usually be an integer mode.
 
diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi
index b5cb240..0abf394 100644
--- a/gcc/doc/tm.texi
+++ b/gcc/doc/tm.texi
@@ -8800,6 +8800,25 @@ Define this macro on machine that have comparison operations that return
 floating-point values.  If there are no such operations, do not define
 this macro.
 
+@findex CLZ_DEFINED_VALUE_AT_ZERO
+@findex CTZ_DEFINED_VALUE_AT_ZERO
+@item CLZ_DEFINED_VALUE_AT_ZERO (@var{mode}, @var{value})
+@itemx CTZ_DEFINED_VALUE_AT_ZERO (@var{mode}, @var{value})
+A C expression that evaluates to true if the architecture defines a value
+for @code{clz} or @code{ctz} with a zero operand.  If so, @var{value}
+should be set to this value.  If this macro is not defined, the value of
+@code{clz} or @code{ctz} is assumed to be undefined.
+
+This macro must be defined if the target's expansion for @code{ffs}
+relies on a particular value to get correct results.  Otherwise it
+is not necessary, though it may be used to optimize some corner cases.
+
+Note that regardless of this macro the ``definedness'' of @code{clz}
+and @code{ctz} at zero do @emph{not} extend to the builtin functions
+visible to the user.  Thus one may be free to adjust the value at will
+to match the target expansion of these operations without fear of
+breaking the API.
+
 @findex Pmode
 @item Pmode
 An alias for the machine mode for pointers.  On most machines, define
-- 
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