diff options
Diffstat (limited to 'gcc/doc/tm.texi.in')
| -rw-r--r-- | gcc/doc/tm.texi.in | 57 |
1 files changed, 49 insertions, 8 deletions
diff --git a/gcc/doc/tm.texi.in b/gcc/doc/tm.texi.in index 863e843af3d..368afd6b1e7 100644 --- a/gcc/doc/tm.texi.in +++ b/gcc/doc/tm.texi.in @@ -7333,14 +7333,8 @@ Returns the negative of the floating point value @var{x}. Returns the absolute value of @var{x}. @end deftypefn -@deftypefn Macro void REAL_VALUE_TO_INT (HOST_WIDE_INT @var{low}, HOST_WIDE_INT @var{high}, REAL_VALUE_TYPE @var{x}) -Converts a floating point value @var{x} into a double-precision integer -which is then stored into @var{low} and @var{high}. If the value is not -integral, it is truncated. -@end deftypefn - -@deftypefn Macro void REAL_VALUE_FROM_INT (REAL_VALUE_TYPE @var{x}, HOST_WIDE_INT @var{low}, HOST_WIDE_INT @var{high}, enum machine_mode @var{mode}) -Converts a double-precision integer found in @var{low} and @var{high}, +@deftypefn Macro void REAL_VALUE_FROM_INT (REAL_VALUE_TYPE @var{x}, HOST_WIDE_INT @var{val}, enum machine_mode @var{mode}) +Converts a double-precision integer found in @var{val}, into a floating point value which is then stored into @var{x}. The value is truncated to fit in mode @var{mode}. @end deftypefn @@ -8388,3 +8382,50 @@ and the associated definitions of those functions. @hook TARGET_ATOMIC_TEST_AND_SET_TRUEVAL @hook TARGET_HAS_IFUNC_P + +@defmac TARGET_SUPPORTS_WIDE_INT + +On older ports, large integers are stored in @code{CONST_DOUBLE} rtl +objects. Newer ports define @code{TARGET_SUPPORTS_WIDE_INT} to be non +zero to indicate that large integers are stored in +@code{CONST_WIDE_INT} rtl objects. The @code{CONST_WIDE_INT} allows +very large integer constants to be represented. @code{CONST_DOUBLE} +are limited to twice the size of host's @code{HOST_WIDE_INT} +representation. + +Converting a port mostly requires looking for the places where +@code{CONST_DOUBLES} are used with @code{VOIDmode} and replacing that +code with code that accesses @code{CONST_WIDE_INT}s. @samp{"grep -i +const_double"} at the port level gets you to 95% of the changes that +need to be made. There are a few places that require a deeper look. + +@itemize @bullet +@item +There is no equivalent to @code{hval} and @code{lval} for +@code{CONST_WIDE_INT}s. This would be difficult to express in the md +language since there are a variable number of elements. + +Most ports only check that @code{hval} is either 0 or -1 to see if the +value is small. As mentioned above, this will no longer be necessary +since small constants are always @code{CONST_INT}. Of course there +are still a few exceptions, the alpha's constraint used by the zap +instruction certainly requires careful examination by C code. +However, all the current code does is pass the hval and lval to C +code, so evolving the c code to look at the @code{CONST_WIDE_INT} is +not really a large change. + +@item +Because there is no standard template that ports use to materialize +constants, there is likely to be some futzing that is unique to each +port in this code. + +@item +The rtx costs may have to be adjusted to properly account for larger +constants that are represented as @code{CONST_WIDE_INT}. +@end itemize + +All and all it does not takes long to convert ports that the +maintainer is familiar with. + +@end defmac + |