@c Copyright (C) 1988, 1989, 1992, 1994, 1997, 1998, 1999, 2000, 2001, 2002,
-@c 2003, 2004, 2005, 2006, 2007, 2008
+@c 2003, 2004, 2005, 2006, 2007, 2008, 2010, 2011
@c Free Software Foundation, Inc.
@c This is part of the GCC manual.
@c For copying conditions, see the file gcc.texi.
* Side Effects:: Expressions for storing in registers, etc.
* Incdec:: Embedded side-effects for autoincrement addressing.
* Assembler:: Representing @code{asm} with operands.
+* Debug Information:: Expressions representing debugging information.
* Insns:: Expression types for entire insns.
* Calls:: RTL representation of function call insns.
* Sharing:: Some expressions are unique; others *must* be copied.
@item RTX_TERNARY
An RTX code for other three input operations. Currently only
-@code{IF_THEN_ELSE} and @code{VEC_MERGE}.
+@code{IF_THEN_ELSE}, @code{VEC_MERGE}, @code{SIGN_EXTRACT},
+@code{ZERO_EXTRACT}, and @code{FMA}.
@item RTX_INSN
An RTX code for an entire instruction: @code{INSN}, @code{JUMP_INSN}, and
or another @code{COMPONENT_REF}, or null if there is no compile-time
object associated with the reference.
+@findex MEM_OFFSET_KNOWN_P
+@item MEM_OFFSET_KNOWN_P (@var{x})
+True if the offset of the memory reference from @code{MEM_EXPR} is known.
+@samp{MEM_OFFSET (@var{x})} provides the offset if so.
+
@findex MEM_OFFSET
@item MEM_OFFSET (@var{x})
-The offset from the start of @code{MEM_EXPR} as a @code{CONST_INT} rtx.
+The offset from the start of @code{MEM_EXPR}. The value is only valid if
+@samp{MEM_OFFSET_KNOWN_P (@var{x})} is true.
+
+@findex MEM_SIZE_KNOWN_P
+@item MEM_SIZE_KNOWN_P (@var{x})
+True if the size of the memory reference is known.
+@samp{MEM_SIZE (@var{x})} provides its size if so.
@findex MEM_SIZE
@item MEM_SIZE (@var{x})
-The size in bytes of the memory reference as a @code{CONST_INT} rtx.
+The size in bytes of the memory reference.
This is mostly relevant for @code{BLKmode} references as otherwise
-the size is implied by the mode.
+the size is implied by the mode. The value is only valid if
+@samp{MEM_SIZE_KNOWN_P (@var{x})} is true.
@findex MEM_ALIGN
@item MEM_ALIGN (@var{x})
a reference to a non-local label.
Stored in the @code{volatil} field and printed as @samp{/v}.
-@findex MEM_IN_STRUCT_P
-@cindex @code{mem} and @samp{/s}
-@cindex @code{in_struct}, in @code{mem}
-@item MEM_IN_STRUCT_P (@var{x})
-In @code{mem} expressions, nonzero for reference to an entire structure,
-union or array, or to a component of one. Zero for references to a
-scalar variable or through a pointer to a scalar. If both this flag and
-@code{MEM_SCALAR_P} are clear, then we don't know whether this @code{mem}
-is in a structure or not. Both flags should never be simultaneously set.
-Stored in the @code{in_struct} field and printed as @samp{/s}.
-
@findex MEM_KEEP_ALIAS_SET_P
@cindex @code{mem} and @samp{/j}
@cindex @code{jump}, in @code{mem}
are already in a non-addressable component of an aggregate.
Stored in the @code{jump} field and printed as @samp{/j}.
-@findex MEM_SCALAR_P
-@cindex @code{mem} and @samp{/i}
-@cindex @code{return_val}, in @code{mem}
-@item MEM_SCALAR_P (@var{x})
-In @code{mem} expressions, nonzero for reference to a scalar known not
-to be a member of a structure, union, or array. Zero for such
-references and for indirections through pointers, even pointers pointing
-to scalar types. If both this flag and @code{MEM_IN_STRUCT_P} are clear,
-then we don't know whether this @code{mem} is in a structure or not.
-Both flags should never be simultaneously set.
-Stored in the @code{return_val} field and printed as @samp{/i}.
-
@findex MEM_VOLATILE_P
@cindex @code{mem} and @samp{/v}
@cindex @code{asm_input} and @samp{/v}
@findex in_struct
@cindex @samp{/s} in RTL dump
@item in_struct
-In @code{mem} expressions, it is 1 if the memory datum referred to is
-all or part of a structure or array; 0 if it is (or might be) a scalar
-variable. A reference through a C pointer has 0 because the pointer
-might point to a scalar variable. This information allows the compiler
-to determine something about possible cases of aliasing.
-
In @code{reg} expressions, it is 1 if the register has its entire life
contained within the test expression of some loop.
may be used for parameters as well, but this flag is not set on such
uses.
-In @code{mem} expressions, 1 means the memory reference is to a scalar
-known not to be a member of a structure, union, or array.
-
In @code{symbol_ref} expressions, 1 means the referenced symbol is weak.
In @code{call} expressions, 1 means the call is pure.
is a machine-specific set of bits used to represent the result of a
comparison operation. Other machine-specific modes may also be used for
the condition code. These modes are not used on machines that use
-@code{cc0} (see @pxref{Condition Code}).
+@code{cc0} (@pxref{Condition Code}).
@findex BLKmode
@item BLKmode
@findex MODE_CC
@item MODE_CC
Modes representing condition code values. These are @code{CCmode} plus
-any @code{CC_MODE} modes listed in the @file{@var{machine}-modes.def}.
+any @code{CC_MODE} modes listed in the @file{@var{machine}-modes.def}.
@xref{Jump Patterns},
also see @ref{Condition Code}.
Each pseudo register has a natural mode. If it is necessary to
operate on it in a different mode, the register must be
-enclosed in a @code{subreg}.
+enclosed in a @code{subreg}.
There are currently three supported types for the first operand of a
@code{subreg}:
are stored in @var{reg} and the high-order bits are discarded.
When used as an rvalue, the low-order bits of the @code{subreg} are
taken from @var{reg} while the high-order bits may or may not be
-defined.
+defined.
The high-order bits of rvalues are in the following circumstances:
two bytes to an unknown value assuming @code{SUBREG_PROMOTED_VAR_P} is
false.
-@item Normal subregs
+@item Normal subregs
When @var{m1} is at least as narrow as @var{m2} the @code{subreg}
expression is called @dfn{normal}.
integer values, with no particular numerical value. Only real.c and
the runtime libraries care about @code{FLOAT_WORDS_BIG_ENDIAN}.
-Thus,
+Thus,
@smallexample
(subreg:HI (reg:SI @var{x}) 2)
For unsigned widening multiplication, use the same idiom, but with
@code{zero_extend} instead of @code{sign_extend}.
+@findex fma
+@item (fma:@var{m} @var{x} @var{y} @var{z})
+Represents the @code{fma}, @code{fmaf}, and @code{fmal} builtin
+functions that do a combined multiply of @var{x} and @var{y} and then
+adding to@var{z} without doing an intermediate rounding step.
+
@findex div
@findex ss_div
@cindex division
@item (ffs:@var{m} @var{x})
Represents one plus the index of the least significant 1-bit in
@var{x}, represented as an integer of mode @var{m}. (The value is
-zero if @var{x} is zero.) The mode of @var{x} need not be @var{m};
-depending on the target machine, various mode combinations may be
-valid.
+zero if @var{x} is zero.) The mode of @var{x} must be @var{m}
+or @code{VOIDmode}.
+
+@findex clrsb
+@item (clrsb:@var{m} @var{x})
+Represents the number of redundant leading sign bits in @var{x},
+represented as an integer of mode @var{m}, starting at the most
+significant bit position. This is one less than the number of leading
+sign bits (either 0 or 1), with no special cases. The mode of @var{x}
+must be @var{m} or @code{VOIDmode}.
@findex clz
@item (clz:@var{m} @var{x})
If @var{x} is zero, the value is determined by
@code{CLZ_DEFINED_VALUE_AT_ZERO} (@pxref{Misc}). Note that this is one of
the few expressions that is not invariant under widening. The mode of
-@var{x} will usually be an integer mode.
+@var{x} must be @var{m} or @code{VOIDmode}.
@findex ctz
@item (ctz:@var{m} @var{x})
If @var{x} is zero, the value is determined by
@code{CTZ_DEFINED_VALUE_AT_ZERO} (@pxref{Misc}). Except for this case,
@code{ctz(x)} is equivalent to @code{ffs(@var{x}) - 1}. The mode of
-@var{x} will usually be an integer mode.
+@var{x} must be @var{m} or @code{VOIDmode}.
@findex popcount
@item (popcount:@var{m} @var{x})
Represents the number of 1-bits in @var{x}, represented as an integer of
-mode @var{m}. The mode of @var{x} will usually be an integer mode.
+mode @var{m}. The mode of @var{x} must be @var{m} or @code{VOIDmode}.
@findex parity
@item (parity:@var{m} @var{x})
Represents the number of 1-bits modulo 2 in @var{x}, represented as an
-integer of mode @var{m}. The mode of @var{x} will usually be an integer
-mode.
+integer of mode @var{m}. The mode of @var{x} must be @var{m} or
+@code{VOIDmode}.
@findex bswap
@item (bswap:@var{m} @var{x})
Represents the value @var{x} with the order of bytes reversed, carried out
in mode @var{m}, which must be a fixed-point machine mode.
+The mode of @var{x} must be @var{m} or @code{VOIDmode}.
@end table
@node Comparisons
This describes an operation that selects parts of a vector. @var{vec1} is
the source vector, and @var{selection} is a @code{parallel} that contains a
@code{const_int} for each of the subparts of the result vector, giving the
-number of the source subpart that should be stored into it.
+number of the source subpart that should be stored into it.
The result mode @var{m} is either the submode for a single element of
-@var{vec1} (if only one subpart is selected), or another vector mode
+@var{vec1} (if only one subpart is selected), or another vector mode
with that element submode (if multiple subparts are selected).
@findex vec_concat
Note that an insn pattern of @code{(return)} is logically equivalent to
@code{(set (pc) (return))}, but the latter form is never used.
+@findex simple_return
+@item (simple_return)
+Like @code{(return)}, but truly represents only a function return, while
+@code{(return)} may represent an insn that also performs other functions
+of the function epilogue. Like @code{(return)}, this may also occur in
+conditional jumps.
+
@findex call
@item (call @var{function} @var{nargs})
Represents a function call. @var{function} is a @code{mem} expression
brackets stand for a vector; the operand of @code{parallel} is a
vector of expressions. @var{x0}, @var{x1} and so on are individual
side effect expressions---expressions of code @code{set}, @code{call},
-@code{return}, @code{clobber} or @code{use}.
+@code{return}, @code{simple_return}, @code{clobber} or @code{use}.
``In parallel'' means that first all the values used in the individual
side-effects are computed, and second all the actual side-effects are
output operand. They are also distinguished by the output-operand index
number, which is 0, 1, @dots{} for successive output operands.
+@node Debug Information
+@section Variable Location Debug Information in RTL
+@cindex Variable Location Debug Information in RTL
+
+Variable tracking relies on @code{MEM_EXPR} and @code{REG_EXPR}
+annotations to determine what user variables memory and register
+references refer to.
+
+Variable tracking at assignments uses these notes only when they refer
+to variables that live at fixed locations (e.g., addressable
+variables, global non-automatic variables). For variables whose
+location may vary, it relies on the following types of notes.
+
+@table @code
+@findex var_location
+@item (var_location:@var{mode} @var{var} @var{exp} @var{stat})
+Binds variable @code{var}, a tree, to value @var{exp}, an RTL
+expression. It appears only in @code{NOTE_INSN_VAR_LOCATION} and
+@code{DEBUG_INSN}s, with slightly different meanings. @var{mode}, if
+present, represents the mode of @var{exp}, which is useful if it is a
+modeless expression. @var{stat} is only meaningful in notes,
+indicating whether the variable is known to be initialized or
+uninitialized.
+
+@findex debug_expr
+@item (debug_expr:@var{mode} @var{decl})
+Stands for the value bound to the @code{DEBUG_EXPR_DECL} @var{decl},
+that points back to it, within value expressions in
+@code{VAR_LOCATION} nodes.
+
+@end table
+
@node Insns
@section Insns
@cindex insns
insn in the @code{sequence} expression. You can use these expressions
to find the containing @code{sequence} expression.
-Every insn has one of the following six expression codes:
+Every insn has one of the following expression codes:
@table @code
@findex insn
Appears at the start of the function body, after the function
prologue.
+@findex NOTE_INSN_VAR_LOCATION
+@findex NOTE_VAR_LOCATION
+@item NOTE_INSN_VAR_LOCATION
+This note is used to generate variable location debugging information.
+It indicates that the user variable in its @code{VAR_LOCATION} operand
+is at the location given in the RTL expression, or holds a value that
+can be computed by evaluating the RTL expression from that static
+point in the program up to the next such note for the same user
+variable.
+
@end table
These codes are printed symbolically when they appear in debugging dumps.
+
+@findex debug_insn
+@findex INSN_VAR_LOCATION
+@item debug_insn
+The expression code @code{debug_insn} is used for pseudo-instructions
+that hold debugging information for variable tracking at assignments
+(see @option{-fvar-tracking-assignments} option). They are the RTL
+representation of @code{GIMPLE_DEBUG} statements
+(@ref{@code{GIMPLE_DEBUG}}), with a @code{VAR_LOCATION} operand that
+binds a user variable tree to an RTL representation of the
+@code{value} in the corresponding statement. A @code{DEBUG_EXPR} in
+it stands for the value bound to the corresponding
+@code{DEBUG_EXPR_DECL}.
+
+Throughout optimization passes, binding information is kept in
+pseudo-instruction form, so that, unlike notes, it gets the same
+treatment and adjustments that regular instructions would. It is the
+variable tracking pass that turns these pseudo-instructions into var
+location notes, analyzing control flow, value equivalences and changes
+to registers and memory referenced in value expressions, propagating
+the values of debug temporaries and determining expressions that can
+be used to compute the value of each user variable at as many points
+(ranges, actually) in the program as possible.
+
+Unlike @code{NOTE_INSN_VAR_LOCATION}, the value expression in an
+@code{INSN_VAR_LOCATION} denotes a value at that specific point in the
+program, rather than an expression that can be evaluated at any later
+point before an overriding @code{VAR_LOCATION} is encountered. E.g.,
+if a user variable is bound to a @code{REG} and then a subsequent insn
+modifies the @code{REG}, the note location would keep mapping the user
+variable to the register across the insn, whereas the insn location
+would keep the variable bound to the value, so that the variable
+tracking pass would emit another location note for the variable at the
+point in which the register is modified.
+
@end table
@cindex @code{TImode}, in @code{insn}
@table @code
@findex PATTERN
@item PATTERN (@var{i})
-An expression for the side effect performed by this insn. This must be
-one of the following codes: @code{set}, @code{call}, @code{use},
-@code{clobber}, @code{return}, @code{asm_input}, @code{asm_output},
-@code{addr_vec}, @code{addr_diff_vec}, @code{trap_if}, @code{unspec},
-@code{unspec_volatile}, @code{parallel}, @code{cond_exec}, or @code{sequence}. If it is a @code{parallel},
-each element of the @code{parallel} must be one these codes, except that
-@code{parallel} expressions cannot be nested and @code{addr_vec} and
-@code{addr_diff_vec} are not permitted inside a @code{parallel} expression.
+An expression for the side effect performed by this insn. This must
+be one of the following codes: @code{set}, @code{call}, @code{use},
+@code{clobber}, @code{return}, @code{simple_return}, @code{asm_input},
+@code{asm_output}, @code{addr_vec}, @code{addr_diff_vec},
+@code{trap_if}, @code{unspec}, @code{unspec_volatile},
+@code{parallel}, @code{cond_exec}, or @code{sequence}. If it is a
+@code{parallel}, each element of the @code{parallel} must be one these
+codes, except that @code{parallel} expressions cannot be nested and
+@code{addr_vec} and @code{addr_diff_vec} are not permitted inside a
+@code{parallel} expression.
@findex INSN_CODE
@item INSN_CODE (@var{i})
dependencies between instructions within a basic block. Neither a jump
nor a label may come between the related insns. These are only used by
the schedulers and by combine. This is a deprecated data structure.
-Def-use and use-def chains are now preferred.
+Def-use and use-def chains are now preferred.
@findex REG_NOTES
@item REG_NOTES (@var{i})
into hot and cold sections is turned on.
@findex REG_SETJMP
-@item REG_SETJMP
-Appears attached to each @code{CALL_INSN} to @code{setjmp} or a
+@item REG_SETJMP
+Appears attached to each @code{CALL_INSN} to @code{setjmp} or a
related function.
@end table
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