The simplest RTL expressions are those that represent constant values.
INTVAL (exp), which is equivalent to
XWINT (exp, 0). There is only one expression object for the integer value zero; it is the value of the variable
const0_rtx. Likewise, the only expression for integer value one is found in
const1_rtx, the only expression for integer value two is found in
const2_rtx, and the only expression for integer value negative one is found in
constm1_rtx. Any attempt to create an expression of code
const_intand value zero, one, two or negative one will return
constm1_rtxas appropriate. Similarly, there is only one object for the integer whose value is
STORE_FLAG_VALUE. It is found in
const1_rtxwill point to the same object. If
constm1_rtxwill point to the same object.
(const_double:m addr i0 i1 ...)
HOST_BITS_PER_WIDE_INTbits but small enough to fit within twice that number of bits (GNU CC does not provide a mechanism to represent even larger constants). In the latter case, m will be
VOIDmode. addr is used to contain the
memexpression that corresponds to the location in memory that at which the constant can be found. If it has not been allocated a memory location, but is on the chain of all
const_doubleexpressions in this compilation (maintained using an undisplayed field), addr contains
const0_rtx. If it is not on the chain, addr contains
cc0_rtx. addr is customarily accessed with the macro
CONST_DOUBLE_MEMand the chain field via
CONST_DOUBLE_CHAIN. If m is
VOIDmode, the bits of the value are stored in i0 and i1. i0 is customarily accessed with the macro
CONST_DOUBLE_LOWand i1 with
CONST_DOUBLE_HIGH. If the constant is floating point (regardless of its precision), then the number of integers used to store the value depends on the size of
REAL_VALUE_TYPE(see section Cross Compilation and Floating Point). The integers represent a floating point number, but not precisely in the target machine's or host machine's floating point format. To convert them to the precise bit pattern used by the target machine, use the macro
REAL_VALUE_TO_TARGET_DOUBLEand friends (see section Output of Data). The macro
CONST0_RTX (mode)refers to an expression with value 0 in mode mode. If mode mode is of mode class
MODE_INT, it returns
const0_rtx. Otherwise, it returns a
CONST_DOUBLEexpression in mode mode. Similarly, the macro
CONST1_RTX (mode)refers to an expression with value 1 in mode mode and similarly for
symbol_refcontains a mode, which is usually
Pmode. Usually that is the only mode for which a symbol is directly valid.
code_labelthat appears in the instruction sequence to identify the place where the label should go. The reason for using a distinct expression type for code label references is so that jump optimization can distinguish them.
label_refexpressions) combined with
minus. However, not all combinations are valid, since the assembler cannot do arbitrary arithmetic on relocatable symbols. m should be
symbol_ref. The number of bits is machine-dependent and is normally the number of bits specified in an instruction that initializes the high order bits of a register. It is used with
lo_sumto represent the typical two-instruction sequence used in RISC machines to reference a global memory location. m should be
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