diff options
Diffstat (limited to 'gcc/doc/tm.texi')
| -rw-r--r-- | gcc/doc/tm.texi | 60 |
1 files changed, 47 insertions, 13 deletions
diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi index 4eed451..fd4e4fd 100644 --- a/gcc/doc/tm.texi +++ b/gcc/doc/tm.texi @@ -9704,18 +9704,6 @@ 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}, -into a floating point value which is then stored into @var{x}. The -value is truncated to fit in mode @var{mode}. -@end deftypefn - @node Mode Switching @section Mode Switching Instructions @cindex mode switching @@ -11024,7 +11012,7 @@ function version at run-time for a given set of function versions. body must be generated. @end deftypefn -@deftypefn {Target Hook} bool TARGET_CAN_USE_DOLOOP_P (double_int @var{iterations}, double_int @var{iterations_max}, unsigned int @var{loop_depth}, bool @var{entered_at_top}) +@deftypefn {Target Hook} bool TARGET_CAN_USE_DOLOOP_P (const widest_int @var{&iterations}, const widest_int @var{&iterations_max}, unsigned int @var{loop_depth}, bool @var{entered_at_top}) Return true if it is possible to use low-overhead loops (@code{doloop_end} and @code{doloop_begin}) for a particular loop. @var{iterations} gives the exact number of iterations, or 0 if not known. @var{iterations_max} gives @@ -11440,3 +11428,49 @@ If defined, this function returns an appropriate alignment in bits for an atomic @deftypefn {Target Hook} void TARGET_ATOMIC_ASSIGN_EXPAND_FENV (tree *@var{hold}, tree *@var{clear}, tree *@var{update}) ISO C11 requires atomic compound assignments that may raise floating-point exceptions to raise exceptions corresponding to the arithmetic operation whose result was successfully stored in a compare-and-exchange sequence. This requires code equivalent to calls to @code{feholdexcept}, @code{feclearexcept} and @code{feupdateenv} to be generated at appropriate points in the compare-and-exchange sequence. This hook should set @code{*@var{hold}} to an expression equivalent to the call to @code{feholdexcept}, @code{*@var{clear}} to an expression equivalent to the call to @code{feclearexcept} and @code{*@var{update}} to an expression equivalent to the call to @code{feupdateenv}. The three expressions are @code{NULL_TREE} on entry to the hook and may be left as @code{NULL_TREE} if no code is required in a particular place. The default implementation leaves all three expressions as @code{NULL_TREE}. The @code{__atomic_feraiseexcept} function from @code{libatomic} may be of use as part of the code generated in @code{*@var{update}}. @end deftypefn + +@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 nonzero +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} +is limited to twice the size of the host's @code{HOST_WIDE_INT} +representation. + +Converting a port mostly requires looking for the places where +@code{CONST_DOUBLE}s 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 take long to convert ports that the +maintainer is familiar with. + +@end defmac |