--- /dev/null
+/* This file is part of GCC.
+
+GCC is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 3, or (at your option)
+any later version.
+
+GCC is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with GCC; see the file COPYING3. If not see
+<http://www.gnu.org/licenses/>. */
+
+/* This file contains code aimed at optimizing function generated with the
+ use of '-msave-restore. The goal is to identify cases where the call
+ out to the save/restore routines are sub-optimal, and remove the calls
+ in this case.
+
+ As GCC currently makes the choice between using or not using
+ save/restore early on (during the gimple expand pass) once we have
+ selected to use save/restore we are stuck with it. */
+
+#define IN_TARGET_CODE 1
+
+#include "config.h"
+#include "system.h"
+#include "coretypes.h"
+#include "tm.h"
+#include "rtl.h"
+#include "function.h"
+#include "memmodel.h"
+#include "emit-rtl.h"
+#include "target.h"
+#include "basic-block.h"
+#include "bitmap.h"
+#include "df.h"
+#include "tree.h"
+#include "expr.h"
+#include "cfg.h"
+
+/* This file should be included last. */
+#include "hard-reg-set.h"
+
+/* Look in the function prologue for a call to the save stub. Ensure that
+ the instruction is as we expect (see detail below) and if the
+ instruction matches return a pointer to it. Otherwise, return NULL.
+
+ We expect the function prologue to look like this:
+
+ (note NOTE_INSN_BASIC_BLOCK)
+ (insn (parallel [
+ (unspec_volatile [
+ (const_int 2 [0x2])
+ ] UNSPECV_GPR_SAVE)
+ (clobber (reg:SI 5 t0))
+ (clobber (reg:SI 6 t1))])
+ (note NOTE_INSN_PROLOGUE_END)
+
+ Between the NOTE_INSN_BASIC_BLOCK and the GPR_SAVE insn we might find
+ other notes of type NOTE_INSN_DELETED and/or NOTE_INSN_FUNCTION_BEG.
+
+ The parameter BODY is updated to point to the first instruction after
+ the NOTE_INSN_PROLOGUE_END or will be updated to NULL if the prologue
+ end note was not found. */
+
+static rtx_insn *
+riscv_sr_match_prologue (rtx_insn **body)
+{
+ rtx_insn *insn, *bb_note;
+ *body = NULL;
+
+ /* Find the prologue end note. */
+ for (insn = get_insns (); insn != NULL; insn = NEXT_INSN (insn))
+ if (NOTE_P (insn) && NOTE_KIND (insn) == NOTE_INSN_PROLOGUE_END)
+ {
+ *body = NEXT_INSN (insn);
+ break;
+ }
+
+ /* If we don't have the prologue end note and at least one instruction
+ before it, then this function doesn't have the structure we expect. */
+ if (insn == NULL
+ || PREV_INSN (insn) == NULL)
+ return NULL;
+
+ /* The INSN is the end of prologue note, before this we expect to find
+ one real instruction which makes the prologue, and before that we
+ expect to find some number of notes for deleted instructions, the
+ beginning of the function, and finally a basicblock beginning. The
+ following loop checks that this assumption is true. */
+ for (bb_note = PREV_INSN (PREV_INSN (insn));
+ bb_note != NULL;
+ bb_note = PREV_INSN (bb_note))
+ {
+ if (!NOTE_P (bb_note))
+ return NULL;
+ if (NOTE_KIND (bb_note) == NOTE_INSN_BASIC_BLOCK)
+ break;
+ if (NOTE_KIND (bb_note) != NOTE_INSN_DELETED
+ && NOTE_KIND (bb_note) != NOTE_INSN_FUNCTION_BEG)
+ return NULL;
+ }
+ if (bb_note == NULL)
+ return NULL;
+
+ /* Set INSN to point to the actual interesting prologue instruction. */
+ insn = PREV_INSN (insn);
+ if (INSN_P (insn)
+ && INSN_CODE (insn) == CODE_FOR_gpr_save
+ /* Check this is a call to _riscv_save_0. */
+ && GET_CODE (PATTERN (insn)) == PARALLEL
+ && GET_CODE (XVECEXP (PATTERN (insn), 0, 0)) == UNSPEC_VOLATILE
+ && (GET_CODE (XVECEXP (XVECEXP (PATTERN (insn), 0, 0), 0, 0))
+ == CONST_INT)
+ && XINT (XVECEXP (XVECEXP (PATTERN (insn), 0, 0), 0, 0), 0) == 2)
+ return insn;
+
+ return NULL;
+}
+
+/* Find the first instruction in the epilogue of the current function, and
+ return a pointer to that instruction if, and only if, the epilogue has
+ the correct structure that would allow us to optimize out the call to
+ _riscv_restore_0. */
+
+static rtx_insn *
+riscv_sr_match_epilogue (void)
+{
+ /* Find the first instruction in the epilogue. */
+ rtx_insn *insn, *start;
+ for (insn = get_insns (); insn != NULL; insn = NEXT_INSN (insn))
+ if (NOTE_P (insn) && NOTE_KIND (insn) == NOTE_INSN_EPILOGUE_BEG)
+ {
+ insn = NEXT_INSN (insn);
+ break;
+ }
+ if (insn == NULL)
+ return NULL;
+
+ /* At this point INSN is the first instruction in the epilogue. A
+ standard epilogue (of the form we expect to handle) consists of the
+ following instructions:
+
+ 1. A stack_tiesi or stack_tiedi (for RV32 and RV64 respectively),
+
+ 2. An optional use instruction for the register holding the return
+ value. This will be missing in functions with no return value,
+
+ 3. A gpr_restore instruction, and
+
+ 4. A jump instruction of type gpr_restore_return. */
+ start = insn;
+ if (INSN_CODE (insn) != CODE_FOR_stack_tiesi
+ && INSN_CODE (insn) != CODE_FOR_stack_tiedi)
+ return NULL;
+
+ insn = NEXT_INSN (insn);
+ if (INSN_P (insn) && GET_CODE (PATTERN (insn)) == USE)
+ insn = NEXT_INSN (insn);
+
+ if (!INSN_P (insn) || INSN_CODE (insn) != CODE_FOR_gpr_restore)
+ return NULL;
+
+ insn = NEXT_INSN (insn);
+ if (!INSN_P (insn) || INSN_CODE (insn) != CODE_FOR_gpr_restore_return)
+ return NULL;
+
+ return start;
+}
+
+/* Helper for riscv_remove_unneeded_save_restore_calls. If we match the
+ prologue instructions but not the epilogue then we might have the case
+ where the epilogue has been optimized out due to a call to a no-return
+ function. In this case we might be able to remove the prologue too -
+ that's what this function does. PROLOGUE is the matched prolgoue
+ instruction, by the time this function returns the progloue instruction
+ may have been removed. */
+
+static void
+check_for_no_return_call (rtx_insn *prologue)
+{
+ /* Check to see if we have the following pattern:
+
+ PROLOGUE instruction
+ NOTE_INSN_PROLOGUE_END
+ A no-return call instruction
+
+ If we do, then we can remove the prologue instruction safely. Remember
+ that we've already confirmed by this point that the prologue is a call
+ to riscv_save_0. */
+
+ if (dump_file)
+ fprintf (dump_file,
+ "Prologue matched, checking for no-return epilogue.\n");
+
+ rtx_insn *tmp = NEXT_INSN (prologue);
+ if (!NOTE_P (tmp) || NOTE_KIND (tmp) != NOTE_INSN_PROLOGUE_END)
+ return;
+
+ /* Skip any extra notes in here, they're most likely just debug. */
+ do
+ {
+ tmp = NEXT_INSN (tmp);
+ }
+ while (tmp != NULL && NOTE_P (tmp));
+
+ if (tmp == NULL || !INSN_P (tmp))
+ return;
+
+ bool noreturn_p = find_reg_note (tmp, REG_NORETURN, NULL_RTX) != NULL_RTX;
+ if (!CALL_P (tmp) || !noreturn_p)
+ return;
+
+ if (dump_file)
+ fprintf (dump_file,
+ "Prologue call to riscv_save_0 followed by noreturn call, "
+ "removing prologue.\n");
+ remove_insn (prologue);
+}
+
+/* Entry point called from riscv_reorg to remove some unneeded calls to
+ the save and restore stubs. This should only be called when
+ -msave-restore is in use.
+
+ We identify some simple cases where the function looks like this:
+
+ call t0,__riscv_save_0
+ <other-code>
+ call foo
+ tail __riscv_restore_0
+
+ And transform it into something like this:
+
+ <other-code>
+ tail foo
+
+ In the above examples, what can appear in <other-code> is pretty
+ restricted; only caller saved registers can be touched, this prevents
+ any additional calls (as they would write to 'ra'). */
+
+void
+riscv_remove_unneeded_save_restore_calls (void)
+{
+ /* Will point to the first instruction of the function body, after the
+ prologue end note. */
+ rtx_insn *body = NULL;
+
+ /* Should only be called with -msave-restore is in use. */
+ gcc_assert (TARGET_SAVE_RESTORE);
+
+ /* Match the expected prologue and epilogue patterns. If either of these
+ fail to match then we abandon our attempt to optimize this function. */
+ rtx_insn *prologue_matched = riscv_sr_match_prologue (&body);
+ if (prologue_matched == NULL || body == NULL)
+ return;
+
+ rtx_insn *epilogue_matched = riscv_sr_match_epilogue ();
+ if (epilogue_matched == NULL)
+ {
+ check_for_no_return_call (prologue_matched);
+ return;
+ }
+
+ if (dump_file)
+ fprintf (dump_file,
+ "Could be a candidate for save/restore removal\n");
+
+ /* We want to check which registers this function uses. */
+ df_analyze ();
+
+ int call_count = 0;
+ bool good_use = true;
+ int epilogue_count = 0;
+
+ /* Now examine all of the instructions that make up this function, we're
+ looking for call instructions and also double checking register usage
+ while we're at it (see comments below). */
+ basic_block bb;
+ FOR_EACH_BB_FN (bb, cfun)
+ {
+ rtx_insn *insn;
+
+ FOR_BB_INSNS (bb, insn)
+ {
+ if (dump_file)
+ fprintf (dump_file,
+ "Block %d, Insn %d\n", bb->index, INSN_UID (insn));
+
+ /* If we scan the epilogue we will fall foul of our register
+ usage check below (due to it's use of the return address), so
+ once we spot we're at the epilogue, just skip the rest of this
+ block. Scanning the prologue instructions again (if they
+ match the expected pattern) is harmless. */
+ if (NOTE_P (insn)
+ && NOTE_KIND (insn) == NOTE_INSN_EPILOGUE_BEG)
+ {
+ ++epilogue_count;
+ break;
+ }
+
+ if (!INSN_P (insn))
+ continue;
+
+ if (CALL_P (insn))
+ ++call_count;
+ else
+ {
+ df_ref use;
+
+ FOR_EACH_INSN_USE (use, insn)
+ {
+ /* If the function makes use of any registers that are
+ callee saved then we should be saving them in this
+ function, which would suggest that a call to the save
+ and restore functions is required. This would seem to
+ indicate that something has gone wrong above, as we
+ should only get here if we are saving zero registers.
+
+ The one exception to this rule is the return address
+ register used within a call instruction. We can
+ optimize a single call within a function (by making it
+ a tail call), so we skip call instructions here. */
+ if (!call_used_regs[DF_REF_REGNO (use)])
+ {
+ if (dump_file)
+ fprintf (dump_file,
+ "Found unsupported use of callee saved "
+ "register in instruction %d\n",
+ INSN_UID (insn));
+ good_use = false;
+ break;
+ }
+ }
+ if (!good_use)
+ break;
+ }
+ }
+ }
+
+ /* If we used any registers that would indicate a need for a call to a
+ save/restore stub then don't optimize. */
+ if (!good_use)
+ return;
+
+ /* If this function has multiple epilogues, then for now we don't try to
+ optimize it. */
+ if (epilogue_count != 1)
+ return;
+
+ /* We can only optimize functions containing a single call, any more
+ would require us to add instructions to store the return address on
+ the stack (and restore it before we return). We could do this in the
+ future, but for now we don't. A single call can be transformed into
+ a tail call reasonably easily. */
+ if (call_count > 1)
+ {
+ if (dump_file)
+ fprintf (dump_file,
+ "Found too many call instructions\n");
+ return;
+ }
+
+ rtx_insn *epilogue_begin_note = PREV_INSN (epilogue_matched);
+ gcc_assert (NOTE_P (epilogue_begin_note)
+ && NOTE_KIND (epilogue_begin_note) == NOTE_INSN_EPILOGUE_BEG);
+
+ df_finish_pass (false);
+
+ /* Find the first instruction before the function epilogue. */
+ rtx_insn *insn_before_epilogue;
+ for (insn_before_epilogue = PREV_INSN (epilogue_begin_note);
+ NOTE_P (insn_before_epilogue);
+ insn_before_epilogue = PREV_INSN (insn_before_epilogue))
+ ;
+
+ /* Leaf functions will not generate calls to the save/restore stubs, so
+ there's no need for this optimization there. We know this function
+ has no more than 1 call (checked above). To convert this single call
+ into a tail call we rely on the call being the last thing before the
+ epilogue. */
+ if (GET_CODE (insn_before_epilogue) != CALL_INSN)
+ return;
+
+ /* The last instruction in this block, just before the epilogue is a
+ call. We can potentially change this call into a tail call. */
+ rtx_insn *call = insn_before_epilogue;
+
+ /* Transform call in insn to a sibcall, this will only be done if the
+ last thing in the function is a call. */
+ rtx callpat = PATTERN (call);
+ gcc_assert (GET_CODE (callpat) == PARALLEL);
+
+ /* Extract from CALLPAT the information we need to build the sibcall. */
+ rtx target_call = NULL;
+ rtx tmp_rtx = XVECEXP (callpat, 0, 0);
+ rtx set_target = NULL;
+ switch (GET_CODE (tmp_rtx))
+ {
+ case CALL:
+ target_call = tmp_rtx;
+ break;
+
+ case SET:
+ {
+ set_target = XEXP (tmp_rtx, 0);
+ tmp_rtx = XEXP (tmp_rtx, 1);
+ if (GET_CODE (tmp_rtx) != CALL)
+ return;
+ target_call = tmp_rtx;
+ break;
+ }
+
+ default:
+ return;
+ }
+
+ rtx target_mem = XEXP (target_call, 0);
+ if (GET_CODE (target_mem) != MEM)
+ return;
+
+ rtx target = XEXP (target_mem, 0);
+ if (GET_CODE (target) != SYMBOL_REF && GET_CODE (target) != REG)
+ return;
+
+ /* The sibcall instructions can only use a specific subset of
+ registers, we're about to (possibly) move a call through a
+ register from the function body and make it a sibcall. If we're
+ not using an appropriate register then we can't make this change.
+
+ Maybe in some future iteration we could actually scan the
+ function, find a suitable sibcall register, and switch over the
+ registers. But we don't do that yet. */
+ if (GET_CODE (target) == REG
+ && !SIBCALL_REG_P (REGNO (target)))
+ return;
+
+ rtx sibcall = NULL;
+ if (set_target != NULL)
+ sibcall
+ = gen_sibcall_value_internal (set_target, target, const0_rtx);
+ else
+ sibcall = gen_sibcall_internal (target, const0_rtx);
+
+ rtx_insn *before_call = PREV_INSN (call);
+ remove_insn (call);
+ rtx_insn *insn = emit_call_insn_after_setloc (sibcall, before_call,
+ INSN_LOCATION (call));
+ REG_NOTES (insn) = REG_NOTES (call);
+ SIBLING_CALL_P (insn) = 1;
+
+ /* Now update the prologue and epilogue to take account of the
+ changes within the function body. */
+ remove_insn (prologue_matched);
+ remove_insn (NEXT_INSN (NEXT_INSN (NEXT_INSN (epilogue_matched))));
+ remove_insn (NEXT_INSN (NEXT_INSN (epilogue_matched)));
+ remove_insn (NEXT_INSN (epilogue_matched));
+ remove_insn (epilogue_matched);
+
+ if (dump_file)
+ fprintf (dump_file,
+ "Save/restore successfully removed\n");
+}
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