11.7.1 Basic Statements

ASM_EXPR

Used to represent an inline assembly statement. For an inline assembly statement like:

          asm ("mov x, y");

The ASM_STRING macro will return a STRING_CST node for "mov x, y". If the original statement made use of the extended-assembly syntax, then ASM_OUTPUTS, ASM_INPUTS, and ASM_CLOBBERS will be the outputs, inputs, and clobbers for the statement, represented as STRING_CST nodes. The extended-assembly syntax looks like:

          asm ("fsinx %1,%0" : "=f" (result) : "f" (angle));

The first string is the ASM_STRING, containing the instruction template. The next two strings are the output and inputs, respectively; this statement has no clobbers. As this example indicates, “plain” assembly statements are merely a special case of extended assembly statements; they have no cv-qualifiers, outputs, inputs, or clobbers. All of the strings will be NUL-terminated, and will contain no embedded NUL-characters.

If the assembly statement is declared volatile, or if the statement was not an extended assembly statement, and is therefore implicitly volatile, then the predicate ASM_VOLATILE_P will hold of the ASM_EXPR.

DECL_EXPR

Used to represent a local declaration. The DECL_EXPR_DECL macro can be used to obtain the entity declared. This declaration may be a LABEL_DECL, indicating that the label declared is a local label. (As an extension, GCC allows the declaration of labels with scope.) In C, this declaration may be a FUNCTION_DECL, indicating the use of the GCC nested function extension. For more information, 参见Functions.

LABEL_EXPR

Used to represent a label. The LABEL_DECL declared by this statement can be obtained with the LABEL_EXPR_LABEL macro. The IDENTIFIER_NODE giving the name of the label can be obtained from the LABEL_DECL with DECL_NAME.

GOTO_EXPR

Used to represent a goto statement. The GOTO_DESTINATION will usually be a LABEL_DECL. However, if the “computed goto” extension has been used, the GOTO_DESTINATION will be an arbitrary expression indicating the destination. This expression will always have pointer type.

RETURN_EXPR

Used to represent a return statement. Operand 0 represents the value to return. It should either be the RESULT_DECL for the containing function, or a MODIFY_EXPR or INIT_EXPR setting the function's RESULT_DECL. It will be NULL_TREE if the statement was just

          return;

LOOP_EXPR

These nodes represent “infinite” loops. The LOOP_EXPR_BODY represents the body of the loop. It should be executed forever, unless an EXIT_EXPR is encountered.

EXIT_EXPR

These nodes represent conditional exits from the nearest enclosing LOOP_EXPR. The single operand is the condition; if it is nonzero, then the loop should be exited. An EXIT_EXPR will only appear within a LOOP_EXPR.

SWITCH_STMT

Used to represent a switch statement. The SWITCH_STMT_COND is the expression on which the switch is occurring. See the documentation for an IF_STMT for more information on the representation used for the condition. The SWITCH_STMT_BODY is the body of the switch statement. The SWITCH_STMT_TYPE is the original type of switch expression as given in the source, before any compiler conversions.

CASE_LABEL_EXPR

Use to represent a case label, range of case labels, or a default label. If CASE_LOW is NULL_TREE, then this is a default label. Otherwise, if CASE_HIGH is NULL_TREE, then this is an ordinary case label. In this case, CASE_LOW is an expression giving the value of the label. Both CASE_LOW and CASE_HIGH are INTEGER_CST nodes. These values will have the same type as the condition expression in the switch statement.

Otherwise, if both CASE_LOW and CASE_HIGH are defined, the statement is a range of case labels. Such statements originate with the extension that allows users to write things of the form:

          case 2 ... 5:

The first value will be CASE_LOW, while the second will be CASE_HIGH.