Improve documentation of earlyclobber

2014-07-04  Tom de Vries  <tom@codesourcery.com>

	* doc/md.texi (@subsection Constraint Modifier Characters): Clarify
	combination of earlyclobber and read/write modifiers.

From-SVN: r212297

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index a9f535079b361cecb8a2caba8f16fbce9dafa3d7..7637d263554236bf6493437cbfcfcd711cbc2541 100644 (file)
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,8 @@
+2014-07-04  Tom de Vries  <tom@codesourcery.com>
+
+       * doc/md.texi (@subsection Constraint Modifier Characters): Clarify
+       combination of earlyclobber and read/write modifiers.
+
 2014-07-04  Tom de Vries  <tom@codesourcery.com>
 
        * config/aarch64/aarch64-simd.md

diff --git a/gcc/doc/md.texi b/gcc/doc/md.texi
index 539865ea3da83222f7a183d1d391d8be7d663152..fde67d7a01ef6238f31d8b55a9eb7aff44276dfa 100644 (file)
--- a/gcc/doc/md.texi
+++ b/gcc/doc/md.texi
@@ -1582,7 +1582,10 @@ alternatives of this form often allows GCC to produce better code
 when only some of the inputs can be affected by the earlyclobber.
 See, for example, the @samp{mulsi3} insn of the ARM@.
 
-@samp{&} does not obviate the need to write @samp{=}.
+Furthermore, if the @dfn{earlyclobber} operand is also read/write operand, then
+that operand is modified only after it's used.
+
+@samp{&} does not obviate the need to write @samp{=} or @samp{+}.
 
 @cindex @samp{%} in constraint
 @item %