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| <a name="Variable-Location-Debug-Information-in-RTL"></a> |
| <h3 class="section">13.18 Variable Location Debug Information in RTL</h3> |
| <a name="index-Variable-Location-Debug-Information-in-RTL"></a> |
| |
| <p>Variable tracking relies on <code>MEM_EXPR</code> and <code>REG_EXPR</code> |
| annotations to determine what user variables memory and register |
| references refer to. |
| </p> |
| <p>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. |
| </p> |
| <dl compact="compact"> |
| <dd><a name="index-var_005flocation"></a> |
| </dd> |
| <dt><code>(var_location:<var>mode</var> <var>var</var> <var>exp</var> <var>stat</var>)</code></dt> |
| <dd><p>Binds variable <code>var</code>, a tree, to value <var>exp</var>, an RTL |
| expression. It appears only in <code>NOTE_INSN_VAR_LOCATION</code> and |
| <code>DEBUG_INSN</code>s, with slightly different meanings. <var>mode</var>, if |
| present, represents the mode of <var>exp</var>, which is useful if it is a |
| modeless expression. <var>stat</var> is only meaningful in notes, |
| indicating whether the variable is known to be initialized or |
| uninitialized. |
| </p> |
| <a name="index-debug_005fexpr"></a> |
| </dd> |
| <dt><code>(debug_expr:<var>mode</var> <var>decl</var>)</code></dt> |
| <dd><p>Stands for the value bound to the <code>DEBUG_EXPR_DECL</code> <var>decl</var>, |
| that points back to it, within value expressions in |
| <code>VAR_LOCATION</code> nodes. |
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