diff options
Diffstat (limited to 'gcc/doc/rtl.texi')
| -rw-r--r-- | gcc/doc/rtl.texi | 24 |
1 files changed, 11 insertions, 13 deletions
diff --git a/gcc/doc/rtl.texi b/gcc/doc/rtl.texi index 922828f..36269a5 100644 --- a/gcc/doc/rtl.texi +++ b/gcc/doc/rtl.texi @@ -2798,11 +2798,17 @@ The value in @var{op} dies in this insn; that is to say, altering the value immediately after this insn would not affect the future behavior of the program. -This does not necessarily mean that the register @var{op} has no useful -value after this insn since it may also be an output of the insn. In -such a case, however, a @code{REG_DEAD} note would be redundant and is -usually not present until after the reload pass, but no code relies on -this fact. +It does not follow that the register @var{op} has no useful value after +this insn since @var{op} is not necessarily modified by this insn. +Rather, no subsequent instruction uses the contents of @var{op}. + +@findex REG_UNUSED +@item REG_UNUSED +The register @var{op} being set by this insn will not be used in a +subsequent insn. This differs from a @code{REG_DEAD} note, which +indicates that the value in an input will not be used subsequently. +These two notes are independent; both may be present for the same +register. @findex REG_INC @item REG_INC @@ -2917,14 +2923,6 @@ Thus, compiler passes prior to register allocation need only check for @code{REG_EQUAL} notes and passes subsequent to register allocation need only check for @code{REG_EQUIV} notes. -@findex REG_UNUSED -@item REG_UNUSED -The register @var{op} being set by this insn will not be used in a -subsequent insn. This differs from a @code{REG_DEAD} note, which -indicates that the value in an input will not be used subsequently. -These two notes are independent; both may be present for the same -register. - @findex REG_WAS_0 @item REG_WAS_0 The single output of this insn contained zero before this insn. |