Gimple statements¶

class gcc.Gimple

A statement, in GCC’s Gimple representation.

The __str__ method is implemented using GCC’s own pretty-printer for gimple, so e.g.:

str(stmt)


might return:

'D.3259 = (long unsigned int) i;'

loc

Source code location of this statement, as a gcc.Location (or None)

block

The lexical block holding this statement, as a gcc.Tree

exprtype

The type of the main expression computed by this statement, as a gcc.Tree (which might be gcc.VoidType)

str_no_uid

A string representation of this statement, like str(), but without including any internal UIDs.

This is intended for use in selftests that compare output against some expected value, to avoid embedding values that change into the expected output.

For example, given an assignment to a temporary, the str(stmt) for the gcc.GimpleAssign might be:

'D.3259 = (long unsigned int) i;'


where the UID “3259” is liable to change from compile to compile, whereas the stmt.str_no_uid has value:

'D.xxxx = (long unsigned int) i;'


which won’t arbitrarily change each time.

walk_tree(callback, *args, **kwargs)

Visit all gcc.Tree nodes associated with this statement, potentially more than once each. This will visit both the left-hand-side and right-hand-side operands of the statement (if any), and recursively visit any of their child nodes.

For each node, the callback is invoked, supplying the node, and any extra positional and keyword arguments passed to walk_tree:

callback(node, *args, **kwargs)


If the callback returns a true value, the traversal stops, and that gcc.Tree is the result of the call to walk_tree. Otherwise, the traversal continues, and walk_tree eventually returns None.

gcc.Gimple has various subclasses, each corresponding to the one of the kinds of statement within GCC’s internal representation.

The following subclasses have been wrapped for use from Python scripts:

Subclass Meaning
gcc.GimpleAsm One or more inline assembly statements
gcc.GimpleAssign

An assignment of an expression to an l-value:

LHS = RHS1 EXPRCODE RHS2;

gcc.GimpleCall

A function call:

[ LHS = ] FN(ARG1, ..., ARGN);

gcc.GimpleCond

A conditional jump, of the form:

if (LHS EXPRCODE RHS) goto TRUE_LABEL else goto FALSE_LABEL;

gcc.GimpleLabel

A label statement (jump target):

LABEL:

gcc.GimpleNop The “do nothing” statement
gcc.GimplePhi

Used in the SSA passes:

LHS = PHI <ARG1, ..., ARGN>;

gcc.GimpleReturn

A “return” statement:

RETURN [RETVAL];

gcc.GimpleSwitch

A switch statement:

switch (INDEXVAR)
{
case LAB1: ...; break;
...
case LABN: ...; break;
default: ...
}


There are some additional subclasses that have not yet been fully wrapped by the Python plugin (email the gcc-python-plugin’s mailing list if you’re interested in working with these):

Subclass Meaning
gcc.GimpleBind A lexical scope
gcc.GimpleCatch An exception handler
gcc.GimpleDebug A debug statement
gcc.GimpleEhDispatch Used in exception-handling
gcc.GimpleEhFilter Used in exception-handling
gcc.GimpleEhMustNotThrow Used in exception-handling
gcc.GimpleErrorMark A dummy statement used for handling internal errors
gcc.GimpleGoto An unconditional jump
gcc.GimpleOmpAtomicLoad Used for implementing OpenMP
gcc.GimpleOmpAtomicStore (ditto)
gcc.GimpleOmpContinue (ditto)
gcc.GimpleOmpCritical (ditto)
gcc.GimpleOmpFor (ditto)
gcc.GimpleOmpMaster (ditto)
gcc.GimpleOmpOrdered (ditto)
gcc.GimpleOmpParallel (ditto)
gcc.GimpleOmpReturn (ditto)
gcc.GimpleOmpSection (ditto)
gcc.GimpleOmpSections (ditto)
gcc.GimpleOmpSectionsSwitch (ditto)
gcc.GimpleOmpSingle (ditto)
gcc.GimpleOmpTask (ditto)
gcc.GimplePredict A hint for branch prediction
gcc.GimpleResx Resumes execution after an exception
gcc.GimpleTry A try/catch or try/finally statement
gcc.GimpleWithCleanupExpr Internally used when generating GIMPLE
class gcc.GimpleAsm

Subclass of gcc.Gimple: a fragment of inline assembler code.

string

The inline assembler code, as a str.

class gcc.GimpleAssign

Subclass of gcc.Gimple: an assignment of an expression to an l-value:

LHS = RHS1 EXPRCODE RHS2;

lhs

Left-hand-side of the assignment, as a gcc.Tree

rhs

The operands on the right-hand-side of the expression, as a list of gcc.Tree instances (either of length 1 or length 2, depending on the expression).

exprcode

The kind of the expression, as an gcc.Tree subclass (the type itself, not an instance)

class gcc.GimpleCall

Subclass of gcc.Gimple: an invocation of a function, potentially assigning the result to an l-value:

[ LHS = ] FN(ARG1, ..., ARGN);

lhs

Left-hand-side of the assignment, as a gcc.Tree, or None

rhs

The operands on the right-hand-side of the expression, as a list of gcc.Tree instances

fn

The function being called, as a gcc.Tree

fndecl

The declaration of the function being called (if any), as a gcc.Tree

args

The arguments for the call, as a list of gcc.Tree

noreturn

(boolean) Has this call been marked as not returning? (e.g. a call to exit)

class gcc.GimpleReturn

Subclass of gcc.Gimple: a “return” statement, signifying the end of a gcc.BasicBlock:

RETURN [RETVAL];

retval

The return value, as a gcc.Tree, or None.

class gcc.GimpleCond

Subclass of gcc.Gimple: a conditional jump, of the form:

if (LHS EXPRCODE RHS) goto TRUE_LABEL else goto FALSE_LABEL

lhs

Left-hand-side of the comparison, as a gcc.Tree

exprcode

The comparison predicate, as a gcc.Comparison subclass (the type itself, not an instance). For example, the gcc.GimpleCond statement for this fragment of C code:

if (a == b)


would have stmt.exprcode == gcc.EqExpr

rhs

The right-hand-side of the comparison, as a gcc.Tree

true_label

The gcc.LabelDecl node used as the jump target for when the comparison is true

false_label

The gcc.LabelDecl node used as the jump target for when the comparison is false

Note that a C conditional of the form:

if (some_int) {suiteA} else {suiteB}


is implicitly expanded to:

if (some_int != 0) {suiteA} else {suiteB}


and this becomes a gcc.GimpleCond with lhs as the integer, exprcode as <type ‘gcc.NeExpr’>, and rhs as gcc.IntegerCst(0).

class gcc.GimplePhi

Subclass of gcc.Gimple used in the SSA passes: a “PHI” or “phoney” function, for merging the various possible values a variable can have based on the edge that we entered this gcc.BasicBlock on:

LHS = PHI <ARG1, ..., ARGN>;

lhs

Left-hand-side of the assignment, as a gcc.SsaName

args

A list of (gcc.Tree, gcc.Edge) pairs representing the possible (expr, edge) inputs. Each expr is either a gcc.SsaName or a gcc.Constant

class gcc.GimpleSwitch

Subclass of gcc.Gimple: a switch statement, signifying the end of a gcc.BasicBlock:

switch (INDEXVAR)
{
case LAB1: ...; break;
...
case LABN: ...; break;
default: ...
}

indexvar

The index variable used by the switch statement, as a gcc.Tree

labels

The labels of the switch statement, as a list of gcc.CaseLabelExpr.

The initial label in the list is always the default.

class gcc.GimpleLabel

Subclass of gcc.Gimple, representing a “label” statement:

.. py:attribute:: labels

The underlying gcc.LabelDecl node representing this jump target
class gcc.GimpleAssign

Subclass of gcc.Gimple: an assignment of an expression to an l-value:

LHS = RHS1 EXPRCODE RHS2;

lhs

Left-hand-side of the assignment, as a gcc.Tree

rhs

The operands on the right-hand-side of the expression, as a list of gcc.Tree instances (either of length 1 or length 2, depending on the expression).

exprcode

The kind of the expression, as an gcc.Tree subclass (the type itself, not an instance)

class gcc.GimpleNop
Subclass of gcc.Gimple, representing a “do-nothing” statement (a.k.a. “no operation”).