GNU Compiler Collection (GCC) Internals: GIMPLE_DEBUG

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#### 12.8.7 `GIMPLE_DEBUG`

GIMPLE function: gdebug *gimple_build_debug_bind (tree var, tree value, gimple stmt)

  Build a `GIMPLE_DEBUG` statement with `GIMPLE_DEBUG_BIND` `subcode`. The effect of this statement is to tell debug information generation machinery that the value of user variable `var` is given by `value` at that point, and to remain with that value until `var` runs out of scope, a dynamically-subsequent debug bind statement overrides the binding, or conflicting values reach a control flow merge point. Even if components of the `value` expression change afterwards, the variable is supposed to retain the same value, though not necessarily the same location.

  It is expected that `var` be most often a tree for automatic user variables (`VAR_DECL` or `PARM_DECL`) that satisfy the requirements for gimple registers, but it may also be a tree for a scalarized component of a user variable (`ARRAY_REF`, `COMPONENT_REF`), or a debug temporary (`DEBUG_EXPR_DECL`).

  As for `value`, it can be an arbitrary tree expression, but it is recommended that it be in a suitable form for a gimple assignment `RHS`. It is not expected that user variables that could appear as `var` ever appear in `value`, because in the latter we’d have their `SSA_NAME`s instead, but even if they were not in SSA form, user variables appearing in `value` are to be regarded as part of the executable code space, whereas those in `var` are to be regarded as part of the source code space. There is no way to refer to the value bound to a user variable within a `value` expression.

  If `value` is `GIMPLE_DEBUG_BIND_NOVALUE`, debug information generation machinery is informed that the variable `var` is unbound, i.e., that its value is indeterminate, which sometimes means it is really unavailable, and other times that the compiler could not keep track of it.

  Block and location information for the newly-created stmt are taken from `stmt`, if given.

GIMPLE function: tree gimple_debug_bind_get_var (gimple stmt)

  Return the user variable var that is bound at `stmt`.

GIMPLE function: tree gimple_debug_bind_get_value (gimple stmt)

  Return the value expression that is bound to a user variable at `stmt`.

GIMPLE function: tree * gimple_debug_bind_get_value_ptr (gimple stmt)

  Return a pointer to the value expression that is bound to a user variable at `stmt`.

GIMPLE function: void gimple_debug_bind_set_var (gimple stmt, tree var)

  Modify the user variable bound at `stmt` to var.

GIMPLE function: void gimple_debug_bind_set_value (gimple stmt, tree var)

  Modify the value bound to the user variable bound at `stmt` to value.

GIMPLE function: void gimple_debug_bind_reset_value (gimple stmt)

  Modify the value bound to the user variable bound at `stmt` so that the variable becomes unbound.

GIMPLE function: bool gimple_debug_bind_has_value_p (gimple stmt)

  Return `TRUE` if `stmt` binds a user variable to a value, and `FALSE` if it unbinds the variable.

GIMPLE function: gimple gimple_build_debug_begin_stmt (tree block, location_t location)

  Build a `GIMPLE_DEBUG` statement with `GIMPLE_DEBUG_BEGIN_STMT` `subcode`. The effect of this statement is to tell debug information generation machinery that the user statement at the given `location` and `block` starts at the point at which the statement is inserted. The intent is that side effects (e.g. variable bindings) of all prior user statements are observable, and that none of the side effects of subsequent user statements are.

GIMPLE function: gimple gimple_build_debug_inline_entry (tree block, location_t location)

  Build a `GIMPLE_DEBUG` statement with `GIMPLE_DEBUG_INLINE_ENTRY` `subcode`. The effect of this statement is to tell debug information generation machinery that a function call at `location` underwent inline substitution, that `block` is the enclosing lexical block created for the substitution, and that at the point of the program in which the stmt is inserted, all parameters for the inlined function are bound to the respective arguments, and none of the side effects of its stmts are observable.

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