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Diffstat (limited to 'gcc/tm.texi')
| -rw-r--r-- | gcc/tm.texi | 20 |
1 files changed, 14 insertions, 6 deletions
diff --git a/gcc/tm.texi b/gcc/tm.texi index 4648778daf9..90e5e908fee 100644 --- a/gcc/tm.texi +++ b/gcc/tm.texi @@ -2088,17 +2088,25 @@ should be the maximum value of @code{HARD_REGNO_NREGS (@var{regno}, This macro helps control the handling of multiple-word values in the reload pass. -@item CLASS_CANNOT_CHANGE_SIZE -If defined, a C expression for a class that contains registers which the -compiler must always access in a mode that is the same size as the mode -in which it loaded the register. +@item CLASS_CANNOT_CHANGE_MODE +If defined, a C expression for a class that contains registers for +which the compiler may not change modes arbitrarily. + +@item CLASS_CANNOT_CHANGE_MODE_P(@var{from}, @var{to}) +A C expression that is true if, for a register in +@code{CLASS_CANNOT_CHANGE_MODE}, the requested mode punning is illegal. For the example, loading 32-bit integer or floating-point objects into floating-point registers on the Alpha extends them to 64-bits. Therefore loading a 64-bit object and then storing it as a 32-bit object does not store the low-order 32-bits, as would be the case for a normal -register. Therefore, @file{alpha.h} defines this macro as -@code{FLOAT_REGS}. +register. Therefore, @file{alpha.h} defines @code{CLASS_CANNOT_CHANGE_MODE} +as @code{FLOAT_REGS} and @code{CLASS_CANNOT_CHANGE_MODE_P} restricts +mode changes to same-size modes. + +Compare this to IA-64, which extends floating-point values to 82-bits, +and stores 64-bit integers in a different format than 64-bit doubles. +Therefore @code{CLASS_CANNOT_CHANGE_MODE_P} is always true. @end table Three other special macros describe which operands fit which constraint |