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71<a name="Flags"></a>
72<div class="header">
73<p>
74Next: <a href="Machine-Modes.html#Machine-Modes" accesskey="n" rel="next">Machine Modes</a>, Previous: <a href="Special-Accessors.html#Special-Accessors" accesskey="p" rel="prev">Special Accessors</a>, Up: <a href="RTL.html#RTL" accesskey="u" rel="up">RTL</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
75</div>
76<hr>
77<a name="Flags-in-an-RTL-Expression"></a>
78<h3 class="section">13.5 Flags in an RTL Expression</h3>
79<a name="index-flags-in-RTL-expression"></a>
80
81<p>RTL expressions contain several flags (one-bit bit-fields)
82that are used in certain types of expression. Most often they
83are accessed with the following macros, which expand into lvalues.
84</p>
85<dl compact="compact">
86<dd><a name="index-CONSTANT_005fPOOL_005fADDRESS_005fP"></a>
87<a name="index-symbol_005fref-and-_002fu"></a>
88<a name="index-unchanging_002c-in-symbol_005fref"></a>
89</dd>
90<dt><code>CONSTANT_POOL_ADDRESS_P (<var>x</var>)</code></dt>
91<dd><p>Nonzero in a <code>symbol_ref</code> if it refers to part of the current
92function&rsquo;s constant pool. For most targets these addresses are in a
93<code>.rodata</code> section entirely separate from the function, but for
94some targets the addresses are close to the beginning of the function.
95In either case GCC assumes these addresses can be addressed directly,
96perhaps with the help of base registers.
97Stored in the <code>unchanging</code> field and printed as &lsquo;<samp>/u</samp>&rsquo;.
98</p>
99<a name="index-RTL_005fCONST_005fCALL_005fP"></a>
100<a name="index-call_005finsn-and-_002fu"></a>
101<a name="index-unchanging_002c-in-call_005finsn"></a>
102</dd>
103<dt><code>RTL_CONST_CALL_P (<var>x</var>)</code></dt>
104<dd><p>In a <code>call_insn</code> indicates that the insn represents a call to a
105const function. Stored in the <code>unchanging</code> field and printed as
106&lsquo;<samp>/u</samp>&rsquo;.
107</p>
108<a name="index-RTL_005fPURE_005fCALL_005fP"></a>
109<a name="index-call_005finsn-and-_002fi"></a>
110<a name="index-return_005fval_002c-in-call_005finsn"></a>
111</dd>
112<dt><code>RTL_PURE_CALL_P (<var>x</var>)</code></dt>
113<dd><p>In a <code>call_insn</code> indicates that the insn represents a call to a
114pure function. Stored in the <code>return_val</code> field and printed as
115&lsquo;<samp>/i</samp>&rsquo;.
116</p>
117<a name="index-RTL_005fCONST_005fOR_005fPURE_005fCALL_005fP"></a>
118<a name="index-call_005finsn-and-_002fu-or-_002fi"></a>
119</dd>
120<dt><code>RTL_CONST_OR_PURE_CALL_P (<var>x</var>)</code></dt>
121<dd><p>In a <code>call_insn</code>, true if <code>RTL_CONST_CALL_P</code> or
122<code>RTL_PURE_CALL_P</code> is true.
123</p>
124<a name="index-RTL_005fLOOPING_005fCONST_005fOR_005fPURE_005fCALL_005fP"></a>
125<a name="index-call_005finsn-and-_002fc"></a>
126<a name="index-call_002c-in-call_005finsn"></a>
127</dd>
128<dt><code>RTL_LOOPING_CONST_OR_PURE_CALL_P (<var>x</var>)</code></dt>
129<dd><p>In a <code>call_insn</code> indicates that the insn represents a possibly
130infinite looping call to a const or pure function. Stored in the
131<code>call</code> field and printed as &lsquo;<samp>/c</samp>&rsquo;. Only true if one of
132<code>RTL_CONST_CALL_P</code> or <code>RTL_PURE_CALL_P</code> is true.
133</p>
134<a name="index-INSN_005fANNULLED_005fBRANCH_005fP"></a>
135<a name="index-jump_005finsn-and-_002fu"></a>
136<a name="index-call_005finsn-and-_002fu-1"></a>
137<a name="index-insn-and-_002fu"></a>
138<a name="index-unchanging_002c-in-jump_005finsn_002c-call_005finsn-and-insn"></a>
139</dd>
140<dt><code>INSN_ANNULLED_BRANCH_P (<var>x</var>)</code></dt>
141<dd><p>In a <code>jump_insn</code>, <code>call_insn</code>, or <code>insn</code> indicates
142that the branch is an annulling one. See the discussion under
143<code>sequence</code> below. Stored in the <code>unchanging</code> field and
144printed as &lsquo;<samp>/u</samp>&rsquo;.
145</p>
146<a name="index-INSN_005fDELETED_005fP"></a>
147<a name="index-insn-and-_002fv"></a>
148<a name="index-call_005finsn-and-_002fv"></a>
149<a name="index-jump_005finsn-and-_002fv"></a>
150<a name="index-code_005flabel-and-_002fv"></a>
151<a name="index-jump_005ftable_005fdata-and-_002fv"></a>
152<a name="index-barrier-and-_002fv"></a>
153<a name="index-note-and-_002fv"></a>
154<a name="index-volatil_002c-in-insn_002c-call_005finsn_002c-jump_005finsn_002c-code_005flabel_002c-jump_005ftable_005fdata_002c-barrier_002c-and-note"></a>
155</dd>
156<dt><code>INSN_DELETED_P (<var>x</var>)</code></dt>
157<dd><p>In an <code>insn</code>, <code>call_insn</code>, <code>jump_insn</code>, <code>code_label</code>,
158<code>jump_table_data</code>, <code>barrier</code>, or <code>note</code>,
159nonzero if the insn has been deleted. Stored in the
160<code>volatil</code> field and printed as &lsquo;<samp>/v</samp>&rsquo;.
161</p>
162<a name="index-INSN_005fFROM_005fTARGET_005fP"></a>
163<a name="index-insn-and-_002fs"></a>
164<a name="index-jump_005finsn-and-_002fs"></a>
165<a name="index-call_005finsn-and-_002fs"></a>
166<a name="index-in_005fstruct_002c-in-insn-and-jump_005finsn-and-call_005finsn"></a>
167</dd>
168<dt><code>INSN_FROM_TARGET_P (<var>x</var>)</code></dt>
169<dd><p>In an <code>insn</code> or <code>jump_insn</code> or <code>call_insn</code> in a delay
170slot of a branch, indicates that the insn
171is from the target of the branch. If the branch insn has
172<code>INSN_ANNULLED_BRANCH_P</code> set, this insn will only be executed if
173the branch is taken. For annulled branches with
174<code>INSN_FROM_TARGET_P</code> clear, the insn will be executed only if the
175branch is not taken. When <code>INSN_ANNULLED_BRANCH_P</code> is not set,
176this insn will always be executed. Stored in the <code>in_struct</code>
177field and printed as &lsquo;<samp>/s</samp>&rsquo;.
178</p>
179<a name="index-LABEL_005fPRESERVE_005fP"></a>
180<a name="index-code_005flabel-and-_002fi"></a>
181<a name="index-note-and-_002fi"></a>
182<a name="index-in_005fstruct_002c-in-code_005flabel-and-note"></a>
183</dd>
184<dt><code>LABEL_PRESERVE_P (<var>x</var>)</code></dt>
185<dd><p>In a <code>code_label</code> or <code>note</code>, indicates that the label is referenced by
186code or data not visible to the RTL of a given function.
187Labels referenced by a non-local goto will have this bit set. Stored
188in the <code>in_struct</code> field and printed as &lsquo;<samp>/s</samp>&rsquo;.
189</p>
190<a name="index-LABEL_005fREF_005fNONLOCAL_005fP"></a>
191<a name="index-label_005fref-and-_002fv"></a>
192<a name="index-reg_005flabel-and-_002fv"></a>
193<a name="index-volatil_002c-in-label_005fref-and-reg_005flabel"></a>
194</dd>
195<dt><code>LABEL_REF_NONLOCAL_P (<var>x</var>)</code></dt>
196<dd><p>In <code>label_ref</code> and <code>reg_label</code> expressions, nonzero if this is
197a reference to a non-local label.
198Stored in the <code>volatil</code> field and printed as &lsquo;<samp>/v</samp>&rsquo;.
199</p>
200<a name="index-MEM_005fKEEP_005fALIAS_005fSET_005fP"></a>
201<a name="index-mem-and-_002fj"></a>
202<a name="index-jump_002c-in-mem"></a>
203</dd>
204<dt><code>MEM_KEEP_ALIAS_SET_P (<var>x</var>)</code></dt>
205<dd><p>In <code>mem</code> expressions, 1 if we should keep the alias set for this
206mem unchanged when we access a component. Set to 1, for example, when we
207are already in a non-addressable component of an aggregate.
208Stored in the <code>jump</code> field and printed as &lsquo;<samp>/j</samp>&rsquo;.
209</p>
210<a name="index-MEM_005fVOLATILE_005fP"></a>
211<a name="index-mem-and-_002fv"></a>
212<a name="index-asm_005finput-and-_002fv"></a>
213<a name="index-asm_005foperands-and-_002fv"></a>
214<a name="index-volatil_002c-in-mem_002c-asm_005foperands_002c-and-asm_005finput"></a>
215</dd>
216<dt><code>MEM_VOLATILE_P (<var>x</var>)</code></dt>
217<dd><p>In <code>mem</code>, <code>asm_operands</code>, and <code>asm_input</code> expressions,
218nonzero for volatile memory references.
219Stored in the <code>volatil</code> field and printed as &lsquo;<samp>/v</samp>&rsquo;.
220</p>
221<a name="index-MEM_005fNOTRAP_005fP"></a>
222<a name="index-mem-and-_002fc"></a>
223<a name="index-call_002c-in-mem"></a>
224</dd>
225<dt><code>MEM_NOTRAP_P (<var>x</var>)</code></dt>
226<dd><p>In <code>mem</code>, nonzero for memory references that will not trap.
227Stored in the <code>call</code> field and printed as &lsquo;<samp>/c</samp>&rsquo;.
228</p>
229<a name="index-MEM_005fPOINTER"></a>
230<a name="index-mem-and-_002ff"></a>
231<a name="index-frame_005frelated_002c-in-mem"></a>
232</dd>
233<dt><code>MEM_POINTER (<var>x</var>)</code></dt>
234<dd><p>Nonzero in a <code>mem</code> if the memory reference holds a pointer.
235Stored in the <code>frame_related</code> field and printed as &lsquo;<samp>/f</samp>&rsquo;.
236</p>
237<a name="index-REG_005fFUNCTION_005fVALUE_005fP"></a>
238<a name="index-reg-and-_002fi"></a>
239<a name="index-return_005fval_002c-in-reg"></a>
240</dd>
241<dt><code>REG_FUNCTION_VALUE_P (<var>x</var>)</code></dt>
242<dd><p>Nonzero in a <code>reg</code> if it is the place in which this function&rsquo;s
243value is going to be returned. (This happens only in a hard
244register.) Stored in the <code>return_val</code> field and printed as
245&lsquo;<samp>/i</samp>&rsquo;.
246</p>
247<a name="index-REG_005fPOINTER"></a>
248<a name="index-reg-and-_002ff"></a>
249<a name="index-frame_005frelated_002c-in-reg"></a>
250</dd>
251<dt><code>REG_POINTER (<var>x</var>)</code></dt>
252<dd><p>Nonzero in a <code>reg</code> if the register holds a pointer. Stored in the
253<code>frame_related</code> field and printed as &lsquo;<samp>/f</samp>&rsquo;.
254</p>
255<a name="index-REG_005fUSERVAR_005fP"></a>
256<a name="index-reg-and-_002fv"></a>
257<a name="index-volatil_002c-in-reg"></a>
258</dd>
259<dt><code>REG_USERVAR_P (<var>x</var>)</code></dt>
260<dd><p>In a <code>reg</code>, nonzero if it corresponds to a variable present in
261the user&rsquo;s source code. Zero for temporaries generated internally by
262the compiler. Stored in the <code>volatil</code> field and printed as
263&lsquo;<samp>/v</samp>&rsquo;.
264</p>
265<p>The same hard register may be used also for collecting the values of
266functions called by this one, but <code>REG_FUNCTION_VALUE_P</code> is zero
267in this kind of use.
268</p>
269<a name="index-RTX_005fFRAME_005fRELATED_005fP"></a>
270<a name="index-insn-and-_002ff"></a>
271<a name="index-call_005finsn-and-_002ff"></a>
272<a name="index-jump_005finsn-and-_002ff"></a>
273<a name="index-barrier-and-_002ff"></a>
274<a name="index-set-and-_002ff"></a>
275<a name="index-frame_005frelated_002c-in-insn_002c-call_005finsn_002c-jump_005finsn_002c-barrier_002c-and-set"></a>
276</dd>
277<dt><code>RTX_FRAME_RELATED_P (<var>x</var>)</code></dt>
278<dd><p>Nonzero in an <code>insn</code>, <code>call_insn</code>, <code>jump_insn</code>,
279<code>barrier</code>, or <code>set</code> which is part of a function prologue
280and sets the stack pointer, sets the frame pointer, or saves a register.
281This flag should also be set on an instruction that sets up a temporary
282register to use in place of the frame pointer.
283Stored in the <code>frame_related</code> field and printed as &lsquo;<samp>/f</samp>&rsquo;.
284</p>
285<p>In particular, on RISC targets where there are limits on the sizes of
286immediate constants, it is sometimes impossible to reach the register
287save area directly from the stack pointer. In that case, a temporary
288register is used that is near enough to the register save area, and the
289Canonical Frame Address, i.e., DWARF2&rsquo;s logical frame pointer, register
290must (temporarily) be changed to be this temporary register. So, the
291instruction that sets this temporary register must be marked as
292<code>RTX_FRAME_RELATED_P</code>.
293</p>
294<p>If the marked instruction is overly complex (defined in terms of what
295<code>dwarf2out_frame_debug_expr</code> can handle), you will also have to
296create a <code>REG_FRAME_RELATED_EXPR</code> note and attach it to the
297instruction. This note should contain a simple expression of the
298computation performed by this instruction, i.e., one that
299<code>dwarf2out_frame_debug_expr</code> can handle.
300</p>
301<p>This flag is required for exception handling support on targets with RTL
302prologues.
303</p>
304<a name="index-MEM_005fREADONLY_005fP"></a>
305<a name="index-mem-and-_002fu"></a>
306<a name="index-unchanging_002c-in-mem"></a>
307</dd>
308<dt><code>MEM_READONLY_P (<var>x</var>)</code></dt>
309<dd><p>Nonzero in a <code>mem</code>, if the memory is statically allocated and read-only.
310</p>
311<p>Read-only in this context means never modified during the lifetime of the
312program, not necessarily in ROM or in write-disabled pages. A common
313example of the later is a shared library&rsquo;s global offset table. This
314table is initialized by the runtime loader, so the memory is technically
315writable, but after control is transferred from the runtime loader to the
316application, this memory will never be subsequently modified.
317</p>
318<p>Stored in the <code>unchanging</code> field and printed as &lsquo;<samp>/u</samp>&rsquo;.
319</p>
320<a name="index-SCHED_005fGROUP_005fP"></a>
321<a name="index-insn-and-_002fs-1"></a>
322<a name="index-call_005finsn-and-_002fs-1"></a>
323<a name="index-jump_005finsn-and-_002fs-1"></a>
324<a name="index-jump_005ftable_005fdata-and-_002fs"></a>
325<a name="index-in_005fstruct_002c-in-insn_002c-call_005finsn_002c-jump_005finsn-and-jump_005ftable_005fdata"></a>
326</dd>
327<dt><code>SCHED_GROUP_P (<var>x</var>)</code></dt>
328<dd><p>During instruction scheduling, in an <code>insn</code>, <code>call_insn</code>,
329<code>jump_insn</code> or <code>jump_table_data</code>, indicates that the
330previous insn must be scheduled together with this insn. This is used to
331ensure that certain groups of instructions will not be split up by the
332instruction scheduling pass, for example, <code>use</code> insns before
333a <code>call_insn</code> may not be separated from the <code>call_insn</code>.
334Stored in the <code>in_struct</code> field and printed as &lsquo;<samp>/s</samp>&rsquo;.
335</p>
336<a name="index-SET_005fIS_005fRETURN_005fP"></a>
337<a name="index-insn-and-_002fj"></a>
338<a name="index-jump_002c-in-insn"></a>
339</dd>
340<dt><code>SET_IS_RETURN_P (<var>x</var>)</code></dt>
341<dd><p>For a <code>set</code>, nonzero if it is for a return.
342Stored in the <code>jump</code> field and printed as &lsquo;<samp>/j</samp>&rsquo;.
343</p>
344<a name="index-SIBLING_005fCALL_005fP"></a>
345<a name="index-call_005finsn-and-_002fj"></a>
346<a name="index-jump_002c-in-call_005finsn"></a>
347</dd>
348<dt><code>SIBLING_CALL_P (<var>x</var>)</code></dt>
349<dd><p>For a <code>call_insn</code>, nonzero if the insn is a sibling call.
350Stored in the <code>jump</code> field and printed as &lsquo;<samp>/j</samp>&rsquo;.
351</p>
352<a name="index-STRING_005fPOOL_005fADDRESS_005fP"></a>
353<a name="index-symbol_005fref-and-_002ff"></a>
354<a name="index-frame_005frelated_002c-in-symbol_005fref"></a>
355</dd>
356<dt><code>STRING_POOL_ADDRESS_P (<var>x</var>)</code></dt>
357<dd><p>For a <code>symbol_ref</code> expression, nonzero if it addresses this function&rsquo;s
358string constant pool.
359Stored in the <code>frame_related</code> field and printed as &lsquo;<samp>/f</samp>&rsquo;.
360</p>
361<a name="index-SUBREG_005fPROMOTED_005fUNSIGNED_005fP"></a>
362<a name="index-subreg-and-_002fu-and-_002fv"></a>
363<a name="index-unchanging_002c-in-subreg"></a>
364<a name="index-volatil_002c-in-subreg"></a>
365</dd>
366<dt><code>SUBREG_PROMOTED_UNSIGNED_P (<var>x</var>)</code></dt>
367<dd><p>Returns a value greater then zero for a <code>subreg</code> that has
368<code>SUBREG_PROMOTED_VAR_P</code> nonzero if the object being referenced is kept
369zero-extended, zero if it is kept sign-extended, and less then zero if it is
370extended some other way via the <code>ptr_extend</code> instruction.
371Stored in the <code>unchanging</code>
372field and <code>volatil</code> field, printed as &lsquo;<samp>/u</samp>&rsquo; and &lsquo;<samp>/v</samp>&rsquo;.
373This macro may only be used to get the value it may not be used to change
374the value. Use <code>SUBREG_PROMOTED_UNSIGNED_SET</code> to change the value.
375</p>
376<a name="index-SUBREG_005fPROMOTED_005fUNSIGNED_005fSET"></a>
377<a name="index-subreg-and-_002fu"></a>
378<a name="index-unchanging_002c-in-subreg-1"></a>
379<a name="index-volatil_002c-in-subreg-1"></a>
380</dd>
381<dt><code>SUBREG_PROMOTED_UNSIGNED_SET (<var>x</var>)</code></dt>
382<dd><p>Set the <code>unchanging</code> and <code>volatil</code> fields in a <code>subreg</code>
383to reflect zero, sign, or other extension. If <code>volatil</code> is
384zero, then <code>unchanging</code> as nonzero means zero extension and as
385zero means sign extension. If <code>volatil</code> is nonzero then some
386other type of extension was done via the <code>ptr_extend</code> instruction.
387</p>
388<a name="index-SUBREG_005fPROMOTED_005fVAR_005fP"></a>
389<a name="index-subreg-and-_002fs"></a>
390<a name="index-in_005fstruct_002c-in-subreg"></a>
391</dd>
392<dt><code>SUBREG_PROMOTED_VAR_P (<var>x</var>)</code></dt>
393<dd><p>Nonzero in a <code>subreg</code> if it was made when accessing an object that
394was promoted to a wider mode in accord with the <code>PROMOTED_MODE</code> machine
395description macro (see <a href="Storage-Layout.html#Storage-Layout">Storage Layout</a>). In this case, the mode of
396the <code>subreg</code> is the declared mode of the object and the mode of
397<code>SUBREG_REG</code> is the mode of the register that holds the object.
398Promoted variables are always either sign- or zero-extended to the wider
399mode on every assignment. Stored in the <code>in_struct</code> field and
400printed as &lsquo;<samp>/s</samp>&rsquo;.
401</p>
402<a name="index-SYMBOL_005fREF_005fUSED"></a>
403<a name="index-used_002c-in-symbol_005fref"></a>
404</dd>
405<dt><code>SYMBOL_REF_USED (<var>x</var>)</code></dt>
406<dd><p>In a <code>symbol_ref</code>, indicates that <var>x</var> has been used. This is
407normally only used to ensure that <var>x</var> is only declared external
408once. Stored in the <code>used</code> field.
409</p>
410<a name="index-SYMBOL_005fREF_005fWEAK"></a>
411<a name="index-symbol_005fref-and-_002fi"></a>
412<a name="index-return_005fval_002c-in-symbol_005fref"></a>
413</dd>
414<dt><code>SYMBOL_REF_WEAK (<var>x</var>)</code></dt>
415<dd><p>In a <code>symbol_ref</code>, indicates that <var>x</var> has been declared weak.
416Stored in the <code>return_val</code> field and printed as &lsquo;<samp>/i</samp>&rsquo;.
417</p>
418<a name="index-SYMBOL_005fREF_005fFLAG"></a>
419<a name="index-symbol_005fref-and-_002fv"></a>
420<a name="index-volatil_002c-in-symbol_005fref"></a>
421</dd>
422<dt><code>SYMBOL_REF_FLAG (<var>x</var>)</code></dt>
423<dd><p>In a <code>symbol_ref</code>, this is used as a flag for machine-specific purposes.
424Stored in the <code>volatil</code> field and printed as &lsquo;<samp>/v</samp>&rsquo;.
425</p>
426<p>Most uses of <code>SYMBOL_REF_FLAG</code> are historic and may be subsumed
427by <code>SYMBOL_REF_FLAGS</code>. Certainly use of <code>SYMBOL_REF_FLAGS</code>
428is mandatory if the target requires more than one bit of storage.
429</p>
430<a name="index-PREFETCH_005fSCHEDULE_005fBARRIER_005fP"></a>
431<a name="index-prefetch-and-_002fv"></a>
432<a name="index-volatile_002c-in-prefetch"></a>
433</dd>
434<dt><code>PREFETCH_SCHEDULE_BARRIER_P (<var>x</var>)</code></dt>
435<dd><p>In a <code>prefetch</code>, indicates that the prefetch is a scheduling barrier.
436No other INSNs will be moved over it.
437Stored in the <code>volatil</code> field and printed as &lsquo;<samp>/v</samp>&rsquo;.
438</p></dd>
439</dl>
440
441<p>These are the fields to which the above macros refer:
442</p>
443<dl compact="compact">
444<dd><a name="index-call"></a>
445<a name="index-_002fc-in-RTL-dump"></a>
446</dd>
447<dt><code>call</code></dt>
448<dd><p>In a <code>mem</code>, 1 means that the memory reference will not trap.
449</p>
450<p>In a <code>call</code>, 1 means that this pure or const call may possibly
451infinite loop.
452</p>
453<p>In an RTL dump, this flag is represented as &lsquo;<samp>/c</samp>&rsquo;.
454</p>
455<a name="index-frame_005frelated"></a>
456<a name="index-_002ff-in-RTL-dump"></a>
457</dd>
458<dt><code>frame_related</code></dt>
459<dd><p>In an <code>insn</code> or <code>set</code> expression, 1 means that it is part of
460a function prologue and sets the stack pointer, sets the frame pointer,
461saves a register, or sets up a temporary register to use in place of the
462frame pointer.
463</p>
464<p>In <code>reg</code> expressions, 1 means that the register holds a pointer.
465</p>
466<p>In <code>mem</code> expressions, 1 means that the memory reference holds a pointer.
467</p>
468<p>In <code>symbol_ref</code> expressions, 1 means that the reference addresses
469this function&rsquo;s string constant pool.
470</p>
471<p>In an RTL dump, this flag is represented as &lsquo;<samp>/f</samp>&rsquo;.
472</p>
473<a name="index-in_005fstruct"></a>
474<a name="index-_002fs-in-RTL-dump"></a>
475</dd>
476<dt><code>in_struct</code></dt>
477<dd><p>In <code>reg</code> expressions, it is 1 if the register has its entire life
478contained within the test expression of some loop.
479</p>
480<p>In <code>subreg</code> expressions, 1 means that the <code>subreg</code> is accessing
481an object that has had its mode promoted from a wider mode.
482</p>
483<p>In <code>label_ref</code> expressions, 1 means that the referenced label is
484outside the innermost loop containing the insn in which the <code>label_ref</code>
485was found.
486</p>
487<p>In <code>code_label</code> expressions, it is 1 if the label may never be deleted.
488This is used for labels which are the target of non-local gotos. Such a
489label that would have been deleted is replaced with a <code>note</code> of type
490<code>NOTE_INSN_DELETED_LABEL</code>.
491</p>
492<p>In an <code>insn</code> during dead-code elimination, 1 means that the insn is
493dead code.
494</p>
495<p>In an <code>insn</code> or <code>jump_insn</code> during reorg for an insn in the
496delay slot of a branch,
4971 means that this insn is from the target of the branch.
498</p>
499<p>In an <code>insn</code> during instruction scheduling, 1 means that this insn
500must be scheduled as part of a group together with the previous insn.
501</p>
502<p>In an RTL dump, this flag is represented as &lsquo;<samp>/s</samp>&rsquo;.
503</p>
504<a name="index-return_005fval"></a>
505<a name="index-_002fi-in-RTL-dump"></a>
506</dd>
507<dt><code>return_val</code></dt>
508<dd><p>In <code>reg</code> expressions, 1 means the register contains
509the value to be returned by the current function. On
510machines that pass parameters in registers, the same register number
511may be used for parameters as well, but this flag is not set on such
512uses.
513</p>
514<p>In <code>symbol_ref</code> expressions, 1 means the referenced symbol is weak.
515</p>
516<p>In <code>call</code> expressions, 1 means the call is pure.
517</p>
518<p>In an RTL dump, this flag is represented as &lsquo;<samp>/i</samp>&rsquo;.
519</p>
520<a name="index-jump"></a>
521<a name="index-_002fj-in-RTL-dump"></a>
522</dd>
523<dt><code>jump</code></dt>
524<dd><p>In a <code>mem</code> expression, 1 means we should keep the alias set for this
525mem unchanged when we access a component.
526</p>
527<p>In a <code>set</code>, 1 means it is for a return.
528</p>
529<p>In a <code>call_insn</code>, 1 means it is a sibling call.
530</p>
531<p>In an RTL dump, this flag is represented as &lsquo;<samp>/j</samp>&rsquo;.
532</p>
533<a name="index-unchanging"></a>
534<a name="index-_002fu-in-RTL-dump"></a>
535</dd>
536<dt><code>unchanging</code></dt>
537<dd><p>In <code>reg</code> and <code>mem</code> expressions, 1 means
538that the value of the expression never changes.
539</p>
540<p>In <code>subreg</code> expressions, it is 1 if the <code>subreg</code> references an
541unsigned object whose mode has been promoted to a wider mode.
542</p>
543<p>In an <code>insn</code> or <code>jump_insn</code> in the delay slot of a branch
544instruction, 1 means an annulling branch should be used.
545</p>
546<p>In a <code>symbol_ref</code> expression, 1 means that this symbol addresses
547something in the per-function constant pool.
548</p>
549<p>In a <code>call_insn</code> 1 means that this instruction is a call to a const
550function.
551</p>
552<p>In an RTL dump, this flag is represented as &lsquo;<samp>/u</samp>&rsquo;.
553</p>
554<a name="index-used"></a>
555</dd>
556<dt><code>used</code></dt>
557<dd><p>This flag is used directly (without an access macro) at the end of RTL
558generation for a function, to count the number of times an expression
559appears in insns. Expressions that appear more than once are copied,
560according to the rules for shared structure (see <a href="Sharing.html#Sharing">Sharing</a>).
561</p>
562<p>For a <code>reg</code>, it is used directly (without an access macro) by the
563leaf register renumbering code to ensure that each register is only
564renumbered once.
565</p>
566<p>In a <code>symbol_ref</code>, it indicates that an external declaration for
567the symbol has already been written.
568</p>
569<a name="index-volatil"></a>
570<a name="index-_002fv-in-RTL-dump"></a>
571</dd>
572<dt><code>volatil</code></dt>
573<dd><a name="index-volatile-memory-references"></a>
574<p>In a <code>mem</code>, <code>asm_operands</code>, or <code>asm_input</code>
575expression, it is 1 if the memory
576reference is volatile. Volatile memory references may not be deleted,
577reordered or combined.
578</p>
579<p>In a <code>symbol_ref</code> expression, it is used for machine-specific
580purposes.
581</p>
582<p>In a <code>reg</code> expression, it is 1 if the value is a user-level variable.
5830 indicates an internal compiler temporary.
584</p>
585<p>In an <code>insn</code>, 1 means the insn has been deleted.
586</p>
587<p>In <code>label_ref</code> and <code>reg_label</code> expressions, 1 means a reference
588to a non-local label.
589</p>
590<p>In <code>prefetch</code> expressions, 1 means that the containing insn is a
591scheduling barrier.
592</p>
593<p>In an RTL dump, this flag is represented as &lsquo;<samp>/v</samp>&rsquo;.
594</p></dd>
595</dl>
596
597<hr>
598<div class="header">
599<p>
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