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| author | Hans-Peter Nilsson <hp@axis.com> | 2011-06-09 23:32:32 +0000 |
|---|---|---|
| committer | Hans-Peter Nilsson <hp@gcc.gnu.org> | 2011-06-09 23:32:32 +0000 |
| commit | 6049a4c8fb26a12b6195169e1a7ec3fb2ff860d4 (patch) | |
| tree | 3f5d585cd04b64f871cc6b63f9c30cdb0ad48244 /gcc/doc | |
| parent | 1f9081d15d2bfd28a5951d87f6e6f3fb254cdbdd (diff) | |
| download | gcc-6049a4c8fb26a12b6195169e1a7ec3fb2ff860d4.zip gcc-6049a4c8fb26a12b6195169e1a7ec3fb2ff860d4.tar.gz gcc-6049a4c8fb26a12b6195169e1a7ec3fb2ff860d4.tar.bz2 | |
tm.texi.in (Register Classes): Document rule for the narrowest register classes.
* doc/tm.texi.in (Register Classes): Document rule for the narrowest
register classes.
* doc/tm.texi: Regenerate.
From-SVN: r174866
Diffstat (limited to 'gcc/doc')
| -rw-r--r-- | gcc/doc/tm.texi | 6 | ||||
| -rw-r--r-- | gcc/doc/tm.texi.in | 6 |
2 files changed, 12 insertions, 0 deletions
diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi index ebc876f..b32ff89 100644 --- a/gcc/doc/tm.texi +++ b/gcc/doc/tm.texi @@ -2337,6 +2337,12 @@ constraints is through machine-dependent operand constraint letters. You can define such letters to correspond to various classes, then use them in operand constraints. +You must define the narrowest register classes for allocatable +registers, so that each class either has no subclasses, or that for +some mode, the move cost between registers within the class is +cheaper than moving a register in the class to or from memory +(@pxref{Costs}). + You should define a class for the union of two classes whenever some instruction allows both classes. For example, if an instruction allows either a floating point (coprocessor) register or a general register for a diff --git a/gcc/doc/tm.texi.in b/gcc/doc/tm.texi.in index 85fcfb1..667b1ef 100644 --- a/gcc/doc/tm.texi.in +++ b/gcc/doc/tm.texi.in @@ -2327,6 +2327,12 @@ constraints is through machine-dependent operand constraint letters. You can define such letters to correspond to various classes, then use them in operand constraints. +You must define the narrowest register classes for allocatable +registers, so that each class either has no subclasses, or that for +some mode, the move cost between registers within the class is +cheaper than moving a register in the class to or from memory +(@pxref{Costs}). + You should define a class for the union of two classes whenever some instruction allows both classes. For example, if an instruction allows either a floating point (coprocessor) register or a general register for a |