fold-mem-offsets: Fix powerpc64le-linux profiledbootstrap [PR111601]

The introduction of the fold-mem-offsets pass breaks profiledbootstrap
on powerpc64le-linux.
From what I can see, the pass works one basic block at a time and
will punt on any non-DEBUG_INSN uses outside of the current block
(I believe because of the
          /* This use affects instructions outside of CAN_FOLD_INSNS.  */
          if (!bitmap_bit_p (&can_fold_insns, INSN_UID (use)))
            return 0;
test and can_fold_insns only set in do_analysis (when processing insns in
current bb, cleared at the end) or results of get_single_def_in_bb
(which are checked to be in the same bb).
But, while get_single_def_in_bb checks for
  if (DF_INSN_LUID (def) > DF_INSN_LUID (insn))
    return NULL;
The basic block in the PR in question has:
...
(insn 212 210 215 25 (set (mem/f:DI (reg/v/f:DI 10 10 [orig:152 last_viable ] [152]) [2 *last_viable_336+0 S8 A64])
        (reg/f:DI 9 9 [orig:155 _342 ] [155])) "pr111601.ii":50:17 683 {*movdi_internal64}
     (expr_list:REG_DEAD (reg/v/f:DI 10 10 [orig:152 last_viable ] [152])
        (nil)))
(insn 215 212 484 25 (set (reg:DI 5 5 [226])
        (const_int 0 [0])) "pr111601.ii":52:12 683 {*movdi_internal64}
     (expr_list:REG_EQUIV (const_int 0 [0])
        (nil)))
(insn 484 215 218 25 (set (reg/v/f:DI 10 10 [orig:152 last_viable ] [152])
        (reg/f:DI 9 9 [orig:155 _342 ] [155])) "pr111601.ii":52:12 683 {*movdi_internal64}
     (nil))
...
(insn 564 214 216 25 (set (reg/v/f:DI 10 10 [orig:152 last_viable ] [152])
        (plus:DI (reg/v/f:DI 10 10 [orig:152 last_viable ] [152])
            (const_int 96 [0x60]))) "pr111601.ii":52:12 66 {*adddi3}
     (nil))
(insn 216 564 219 25 (set (mem/f:DI (reg/v/f:DI 10 10 [orig:152 last_viable ] [152]) [2 _343->next+0 S8 A64])
        (reg:DI 5 5 [226])) "pr111601.ii":52:12 683 {*movdi_internal64}
     (expr_list:REG_DEAD (reg:DI 5 5 [226])
        (nil)))
...
and when asking for all uses of %r10 from def 564, it will see uses
in 216 and 212; the former is after the += 96 addition and gets changed
to load from %r10+96 with the addition being dropped, but there is
the other store which is a use across the backedge and when reached
from other edges certainly doesn't have the + 96 addition anywhere,
so the pass doesn't actually change that location.

This patch adds checks from get_single_def_in_bb to get_uses as well,
in particular check that the (regular non-debug) use only appears in the
same basic block as the definition and that it doesn't appear before it (i.e.
use across backedge).

2023-11-29  Jakub Jelinek  <jakub@redhat.com>

	PR bootstrap/111601
	* fold-mem-offsets.cc (get_uses): Ignore DEBUG_INSN uses.  Otherwise,
	punt if use is in a different basic block from INSN or appears before
	INSN in the same basic block.  Formatting fixes.
	(get_single_def_in_bb): Formatting fixes.
	(fold_offsets_1, pass_fold_mem_offsets::execute): Comment formatting
	fixes.

	* g++.dg/opt/pr111601.C: New test.

2 files changed, 105 insertions, 9 deletions

diff --git a/gcc/fold-mem-offsets.cc b/gcc/fold-mem-offsets.cc
index 6263fc7..7ba5600 100644
--- a/gcc/fold-mem-offsets.cc
+++ b/gcc/fold-mem-offsets.cc
@@ -154,7 +154,7 @@ static int stats_fold_count;
    The definition is desired for REG used in INSN.
    Return the definition insn or NULL if there's no definition with
    the desired criteria.  */
-static rtx_insn*
+static rtx_insn *
 get_single_def_in_bb (rtx_insn *insn, rtx reg)
 {
   df_ref use;
@@ -205,11 +205,10 @@ get_single_def_in_bb (rtx_insn *insn, rtx reg)
 /* Get all uses of REG which is set in INSN.  Return the use list or NULL if a
    use is missing / irregular.  If SUCCESS is not NULL then set it to false if
    there are missing / irregular uses and true otherwise.  */
-static struct df_link*
+static df_link *
 get_uses (rtx_insn *insn, rtx reg, bool *success)
 {
   df_ref def;
-  struct df_link *ref_chain, *ref_link;
 
   if (success)
     *success = false;
@@ -221,18 +220,30 @@ get_uses (rtx_insn *insn, rtx reg, bool *success)
   if (!def)
     return NULL;
 
-  ref_chain = DF_REF_CHAIN (def);
+  df_link *ref_chain = DF_REF_CHAIN (def);
+  int insn_luid = DF_INSN_LUID (insn);
+  basic_block insn_bb = BLOCK_FOR_INSN (insn);
 
-  for (ref_link = ref_chain; ref_link; ref_link = ref_link->next)
+  for (df_link *ref_link = ref_chain; ref_link; ref_link = ref_link->next)
     {
       /* Problem getting a use for this instruction.  */
       if (ref_link->ref == NULL)
 	return NULL;
       if (DF_REF_CLASS (ref_link->ref) != DF_REF_REGULAR)
 	return NULL;
+
+      rtx_insn *use = DF_REF_INSN (ref_link->ref);
+      if (DEBUG_INSN_P (use))
+	continue;
+
       /* We do not handle REG_EQUIV/REG_EQ notes for now.  */
       if (DF_REF_FLAGS (ref_link->ref) & DF_REF_IN_NOTE)
 	return NULL;
+      if (BLOCK_FOR_INSN (use) != insn_bb)
+	return NULL;
+      /* Punt if use appears before def in the basic block.  See PR111601.  */
+      if (DF_INSN_LUID (use) < insn_luid)
+	return NULL;
     }
 
   if (success)
@@ -255,8 +266,7 @@ fold_offsets (rtx_insn *insn, rtx reg, bool analyze, bitmap foldable_insns);
 
     If DO_RECURSION is true and ANALYZE is false then offset that would result
     from folding is computed and is returned through the pointer OFFSET_OUT.
-    The instructions that can be folded are recorded in FOLDABLE_INSNS.
-*/
+    The instructions that can be folded are recorded in FOLDABLE_INSNS.  */
 static bool
 fold_offsets_1 (rtx_insn *insn, bool analyze, bool do_recursion,
 		HOST_WIDE_INT *offset_out, bitmap foldable_insns)
@@ -846,8 +856,8 @@ pass_fold_mem_offsets::execute (function *fn)
   FOR_ALL_BB_FN (bb, fn)
     {
       /* There is a conflict between this pass and RISCV's shorten-memrefs
-	  pass.  For now disable folding if optimizing for size because
-	  otherwise this cancels the effects of shorten-memrefs.  */
+	 pass.  For now disable folding if optimizing for size because
+	 otherwise this cancels the effects of shorten-memrefs.  */
       if (optimize_bb_for_size_p (bb))
 	continue;
 
diff --git a/gcc/testsuite/g++.dg/opt/pr111601.C b/gcc/testsuite/g++.dg/opt/pr111601.C
new file mode 100644
index 0000000..a5019e9
--- /dev/null
+++ b/gcc/testsuite/g++.dg/opt/pr111601.C
@@ -0,0 +1,86 @@
+// PR bootstrap/111601
+// { dg-do run { target c++11 } }
+// { dg-options "-O2 -fno-exceptions -fno-rtti -fprofile-generate" }
+// { dg-require-profiling "-fprofile-generate" }
+// { dg-final { cleanup-coverage-files } }
+
+struct tree_base
+{
+  int code:16;
+};
+struct saved_scope
+{
+  void *pad[14];
+  int x_processing_template_decl;
+};
+struct saved_scope *scope_chain;
+struct z_candidate
+{
+  tree_base *fn;
+  void *pad[11];
+  z_candidate *next;
+  int viable;
+  int flags;
+};
+
+__attribute__((noipa)) struct z_candidate *
+splice_viable (struct z_candidate *cands, bool strict_p, bool *any_viable_p)
+{
+  struct z_candidate *viable;
+  struct z_candidate **last_viable;
+  struct z_candidate **cand;
+  bool found_strictly_viable = false;
+  if (scope_chain->x_processing_template_decl)
+    strict_p = true;
+  viable = (z_candidate *) 0;
+  last_viable = &viable;
+  *any_viable_p = false;
+  cand = &cands;
+  while (*cand)
+    {
+      struct z_candidate *c = *cand;
+      if (!strict_p && (c->viable == 1 || ((int) (c->fn)->code) == 273))
+	{
+	  strict_p = true;
+	  if (viable && !found_strictly_viable)
+	    {
+	      *any_viable_p = false;
+	      *last_viable = cands;
+	      cands = viable;
+	      viable = (z_candidate *) 0;
+	      last_viable = &viable;
+	    }
+	}
+      if (strict_p ? c->viable == 1 : c->viable)
+	{
+	  *last_viable = c;
+	  *cand = c->next;
+	  c->next = (z_candidate *) 0;
+	  last_viable = &c->next;
+	  *any_viable_p = true;
+	  if (c->viable == 1)
+	    found_strictly_viable = true;
+	}
+      else
+	cand = &c->next;
+    }
+  return viable ? viable : cands;
+}
+
+int
+main ()
+{
+  saved_scope s{};
+  scope_chain = &s;
+  z_candidate z[4] = {};
+  z[0].next = &z[1];
+  z[1].viable = 1;
+  z[1].next = &z[2];
+  z[2].viable = 1;
+  z[2].next = &z[3];
+  bool b;
+  z_candidate *c = splice_viable (&z[0], true, &b);
+  if (c != &z[1] || z[1].next != &z[2] || z[2].next)
+    __builtin_abort ();
+  return 0;
+}