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Diffstat (limited to 'gcc/doc/md.texi')
| -rw-r--r-- | gcc/doc/md.texi | 4 |
1 files changed, 3 insertions, 1 deletions
diff --git a/gcc/doc/md.texi b/gcc/doc/md.texi index 7a62eaf..0d9bf91 100644 --- a/gcc/doc/md.texi +++ b/gcc/doc/md.texi @@ -2024,7 +2024,9 @@ This instruction pattern moves data with that machine mode from operand If operand 0 is a @code{subreg} with mode @var{m} of a register whose own mode is wider than @var{m}, the effect of this instruction is to store the specified value in the part of the register that corresponds -to mode @var{m}. The effect on the rest of the register is undefined. +to mode @var{m}. Bits outside of @var{m}, but which are within the +same target word as the @code{subreg} are undefined. Bits which are +outside the target word are left unchanged. This class of patterns is special in several ways. First of all, each of these names up to and including full word size @emph{must} be defined, |