fwprop: Fix single_use_p calculation

Commit efb6bc55a93a ("fwprop: Allow (subreg (mem)) simplifications")
introduced a check that was supposed to look at the propagated def's
number of uses.  It uses insn_info::num_uses (), which in reality
returns the number of uses def's insn has.  The whole change therefore
works only by accident.

Fix by looking at set_info's uses instead of insn_info's uses.  This
requires passing around set_info instead of insn_info.

gcc/ChangeLog:

2021-03-02  Ilya Leoshkevich  <iii@linux.ibm.com>

	* fwprop.c (fwprop_propagation::fwprop_propagation): Look at
	set_info's uses.
	(try_fwprop_subst_note): Use set_info instead of insn_info.
	(try_fwprop_subst_pattern): Likewise.
	(try_fwprop_subst_notes): Likewise.
	(try_fwprop_subst): Likewise.
	(forward_propagate_subreg): Likewise.
	(forward_propagate_and_simplify): Likewise.
	(forward_propagate_into): Likewise.
	* rtl-ssa/accesses.h (set_info::single_nondebug_use) New
	method.
	(set_info::single_nondebug_insn_use): Likewise.
	(set_info::single_phi_use): Likewise.
	* rtl-ssa/member-fns.inl (set_info::single_nondebug_use) New
	method.
	(set_info::single_nondebug_insn_use): Likewise.
	(set_info::single_phi_use): Likewise.

gcc/testsuite/ChangeLog:

	* gcc.target/s390/vector/long-double-asm-abi.c: New test.

4 files changed, 107 insertions, 41 deletions

diff --git a/gcc/fwprop.c b/gcc/fwprop.c
index 4b8a554..d720367 100644
--- a/gcc/fwprop.c
+++ b/gcc/fwprop.c
@@ -175,7 +175,7 @@ namespace
     static const uint16_t CONSTANT = FIRST_SPARE_RESULT << 1;
     static const uint16_t PROFITABLE = FIRST_SPARE_RESULT << 2;
 
-    fwprop_propagation (insn_info *, insn_info *, rtx, rtx);
+    fwprop_propagation (insn_info *, set_info *, rtx, rtx);
 
     bool changed_mem_p () const { return result_flags & CHANGED_MEM; }
     bool folded_to_constants_p () const;
@@ -191,13 +191,13 @@ namespace
   };
 }
 
-/* Prepare to replace FROM with TO in INSN.  */
+/* Prepare to replace FROM with TO in USE_INSN.  */
 
 fwprop_propagation::fwprop_propagation (insn_info *use_insn,
-					insn_info *def_insn, rtx from, rtx to)
+					set_info *def, rtx from, rtx to)
   : insn_propagation (use_insn->rtl (), from, to),
-    single_use_p (def_insn->num_uses () == 1),
-    single_ebb_p (use_insn->ebb () == def_insn->ebb ())
+    single_use_p (def->single_nondebug_use ()),
+    single_ebb_p (use_insn->ebb () == def->ebb ())
 {
   should_check_mems = true;
   should_note_simplifications = true;
@@ -368,24 +368,25 @@ contains_paradoxical_subreg_p (rtx x)
   return false;
 }
 
-/* Try to substitute (set DEST SRC) from DEF_INSN into note NOTE of USE_INSN.
-   Return the number of substitutions on success, otherwise return -1 and
-   leave USE_INSN unchanged.
+/* Try to substitute (set DEST SRC), which defines DEF, into note NOTE of
+   USE_INSN.  Return the number of substitutions on success, otherwise return
+   -1 and leave USE_INSN unchanged.
 
-   If REQUIRE_CONSTANT is true, require all substituted occurences of SRC
+   If REQUIRE_CONSTANT is true, require all substituted occurrences of SRC
    to fold to a constant, so that the note does not use any more registers
    than it did previously.  If REQUIRE_CONSTANT is false, also allow the
    substitution if it's something we'd normally allow for the main
    instruction pattern.  */
 
 static int
-try_fwprop_subst_note (insn_info *use_insn, insn_info *def_insn,
+try_fwprop_subst_note (insn_info *use_insn, set_info *def,
 		       rtx note, rtx dest, rtx src, bool require_constant)
 {
   rtx_insn *use_rtl = use_insn->rtl ();
+  insn_info *def_insn = def->insn ();
 
   insn_change_watermark watermark;
-  fwprop_propagation prop (use_insn, def_insn, dest, src);
+  fwprop_propagation prop (use_insn, def, dest, src);
   if (!prop.apply_to_rvalue (&XEXP (note, 0)))
     {
       if (dump_file && (dump_flags & TDF_DETAILS))
@@ -436,19 +437,20 @@ try_fwprop_subst_note (insn_info *use_insn, insn_info *def_insn,
   return prop.num_replacements;
 }
 
-/* Try to substitute (set DEST SRC) from DEF_INSN into location LOC of
+/* Try to substitute (set DEST SRC), which defines DEF, into location LOC of
    USE_INSN's pattern.  Return true on success, otherwise leave USE_INSN
    unchanged.  */
 
 static bool
 try_fwprop_subst_pattern (obstack_watermark &attempt, insn_change &use_change,
-			  insn_info *def_insn, rtx *loc, rtx dest, rtx src)
+			  set_info *def, rtx *loc, rtx dest, rtx src)
 {
   insn_info *use_insn = use_change.insn ();
   rtx_insn *use_rtl = use_insn->rtl ();
+  insn_info *def_insn = def->insn ();
 
   insn_change_watermark watermark;
-  fwprop_propagation prop (use_insn, def_insn, dest, src);
+  fwprop_propagation prop (use_insn, def, dest, src);
   if (!prop.apply_to_pattern (loc))
     {
       if (dump_file && (dump_flags & TDF_DETAILS))
@@ -538,8 +540,7 @@ try_fwprop_subst_pattern (obstack_watermark &attempt, insn_change &use_change,
     {
       if ((REG_NOTE_KIND (note) == REG_EQUAL
 	   || REG_NOTE_KIND (note) == REG_EQUIV)
-	  && try_fwprop_subst_note (use_insn, def_insn, note,
-				    dest, src, false) < 0)
+	  && try_fwprop_subst_note (use_insn, def, note, dest, src, false) < 0)
 	{
 	  *note_ptr = XEXP (note, 1);
 	  free_EXPR_LIST_node (note);
@@ -554,20 +555,19 @@ try_fwprop_subst_pattern (obstack_watermark &attempt, insn_change &use_change,
   return true;
 }
 
-/* Try to substitute (set DEST SRC) from DEF_INSN into USE_INSN's notes,
+/* Try to substitute (set DEST SRC), which defines DEF, into USE_INSN's notes,
    given that it was not possible to do this for USE_INSN's main pattern.
    Return true on success, otherwise leave USE_INSN unchanged.  */
 
 static bool
-try_fwprop_subst_notes (insn_info *use_insn, insn_info *def_insn,
+try_fwprop_subst_notes (insn_info *use_insn, set_info *def,
 			rtx dest, rtx src)
 {
   rtx_insn *use_rtl = use_insn->rtl ();
   for (rtx note = REG_NOTES (use_rtl); note; note = XEXP (note, 1))
     if ((REG_NOTE_KIND (note) == REG_EQUAL
 	 || REG_NOTE_KIND (note) == REG_EQUIV)
-	&& try_fwprop_subst_note (use_insn, def_insn, note,
-				  dest, src, true) > 0)
+	&& try_fwprop_subst_note (use_insn, def, note, dest, src, true) > 0)
       {
 	confirm_change_group ();
 	return true;
@@ -576,7 +576,7 @@ try_fwprop_subst_notes (insn_info *use_insn, insn_info *def_insn,
   return false;
 }
 
-/* Check whether we could validly substitute (set DEST SRC) from DEF_INSN
+/* Check whether we could validly substitute (set DEST SRC), which defines DEF,
    into USE.  If so, first try performing the substitution in location LOC
    of USE->insn ()'s pattern.  If that fails, try instead to substitute
    into the notes.
@@ -584,10 +584,11 @@ try_fwprop_subst_notes (insn_info *use_insn, insn_info *def_insn,
    Return true on success, otherwise leave USE_INSN unchanged.  */
 
 static bool
-try_fwprop_subst (use_info *use, insn_info *def_insn,
+try_fwprop_subst (use_info *use, set_info *def,
 		  rtx *loc, rtx dest, rtx src)
 {
   insn_info *use_insn = use->insn ();
+  insn_info *def_insn = def->insn ();
 
   auto attempt = crtl->ssa->new_change_attempt ();
   use_array src_uses = remove_note_accesses (attempt, def_insn->uses ());
@@ -622,9 +623,8 @@ try_fwprop_subst (use_info *use, insn_info *def_insn,
   if (!restrict_movement (use_change))
     return false;
 
-  return (try_fwprop_subst_pattern (attempt, use_change, def_insn,
-				    loc, dest, src)
-	  || try_fwprop_subst_notes (use_insn, def_insn, dest, src));
+  return (try_fwprop_subst_pattern (attempt, use_change, def, loc, dest, src)
+	  || try_fwprop_subst_notes (use_insn, def, dest, src));
 }
 
 /* For the given single_set INSN, containing SRC known to be a
@@ -671,7 +671,7 @@ free_load_extend (rtx src, insn_info *insn)
    in REF.  The other parameters are the same.  */
 
 static bool
-forward_propagate_subreg (use_info *use, insn_info *def_insn,
+forward_propagate_subreg (use_info *use, set_info *def,
 			  rtx dest, rtx src, df_ref ref)
 {
   scalar_int_mode int_use_mode, src_mode;
@@ -697,8 +697,7 @@ forward_propagate_subreg (use_info *use, insn_info *def_insn,
 	  && REGNO (SUBREG_REG (src)) >= FIRST_PSEUDO_REGISTER
 	  && GET_MODE (SUBREG_REG (src)) == use_mode
 	  && subreg_lowpart_p (src))
-	return try_fwprop_subst (use, def_insn, loc,
-				 use_reg, SUBREG_REG (src));
+	return try_fwprop_subst (use, def, loc, use_reg, SUBREG_REG (src));
     }
 
   /* If this is a SUBREG of a ZERO_EXTEND or SIGN_EXTEND, and the SUBREG
@@ -725,22 +724,21 @@ forward_propagate_subreg (use_info *use, insn_info *def_insn,
 	  && REG_P (XEXP (src, 0))
 	  && REGNO (XEXP (src, 0)) >= FIRST_PSEUDO_REGISTER
 	  && GET_MODE (XEXP (src, 0)) == use_mode
-	  && !free_load_extend (src, def_insn)
+	  && !free_load_extend (src, def->insn ())
 	  && (targetm.mode_rep_extended (int_use_mode, src_mode)
 	      != (int) GET_CODE (src)))
-	return try_fwprop_subst (use, def_insn, loc, use_reg, XEXP (src, 0));
+	return try_fwprop_subst (use, def, loc, use_reg, XEXP (src, 0));
     }
 
   return false;
 }
 
-/* Try to substitute (set DEST SRC) from DEF_INSN into USE and simplify
+/* Try to substitute (set DEST SRC), which defines DEF, into USE and simplify
    the result, handling cases where DEST is used in a subreg and where
    applying that subreg to SRC results in a useful simplification.  */
 
 static bool
-forward_propagate_subreg (use_info *use, insn_info *def_insn,
-			  rtx dest, rtx src)
+forward_propagate_subreg (use_info *use, set_info *def, rtx dest, rtx src)
 {
   if (!use->includes_subregs () || !REG_P (dest))
     return false;
@@ -755,26 +753,27 @@ forward_propagate_subreg (use_info *use, insn_info *def_insn,
 
   FOR_EACH_INSN_USE (ref, use_rtl)
     if (DF_REF_REGNO (ref) == use->regno ()
-	&& forward_propagate_subreg (use, def_insn, dest, src, ref))
+	&& forward_propagate_subreg (use, def, dest, src, ref))
       return true;
 
   FOR_EACH_INSN_EQ_USE (ref, use_rtl)
     if (DF_REF_REGNO (ref) == use->regno ()
-	&& forward_propagate_subreg (use, def_insn, dest, src, ref))
+	&& forward_propagate_subreg (use, def, dest, src, ref))
       return true;
 
   return false;
 }
 
-/* Try to substitute (set DEST SRC) from DEF_INSN into USE and
+/* Try to substitute (set DEST SRC), which defines DEF, into USE and
    simplify the result.  */
 
 static bool
-forward_propagate_and_simplify (use_info *use, insn_info *def_insn,
+forward_propagate_and_simplify (use_info *use, set_info *def,
 				rtx dest, rtx src)
 {
   insn_info *use_insn = use->insn ();
   rtx_insn *use_rtl = use_insn->rtl ();
+  insn_info *def_insn = def->insn ();
 
   /* ??? This check seems unnecessary.  We should be able to propagate
      into any kind of instruction, regardless of whether it's a single set.
@@ -820,7 +819,7 @@ forward_propagate_and_simplify (use_info *use, insn_info *def_insn,
   /* ??? Unconditionally propagating into PATTERN would work better
      for instructions that have match_dups.  */
   rtx *loc = need_single_set ? &use_set : &PATTERN (use_rtl);
-  return try_fwprop_subst (use, def_insn, loc, dest, src);
+  return try_fwprop_subst (use, def, loc, dest, src);
 }
 
 /* Given a use USE of an insn, if it has a single reaching
@@ -836,7 +835,7 @@ forward_propagate_into (use_info *use, bool reg_prop_only = false)
     return false;
 
   /* Disregard uninitialized uses.  */
-  def_info *def = use->def ();
+  set_info *def = use->def ();
   if (!def)
     return false;
 
@@ -880,8 +879,8 @@ forward_propagate_into (use_info *use, bool reg_prop_only = false)
       && find_reg_note (use_rtl, REG_NON_LOCAL_GOTO, NULL_RTX))
     return false;
 
-  if (forward_propagate_and_simplify (use, def_insn, dest, src)
-      || forward_propagate_subreg (use, def_insn, dest, src))
+  if (forward_propagate_and_simplify (use, def, dest, src)
+      || forward_propagate_subreg (use, def, dest, src))
     return true;
 
   return false;
diff --git a/gcc/rtl-ssa/accesses.h b/gcc/rtl-ssa/accesses.h
index 09ae583..91e64f3 100644
--- a/gcc/rtl-ssa/accesses.h
+++ b/gcc/rtl-ssa/accesses.h
@@ -705,6 +705,19 @@ public:
   // Return true if at least one phi node uses the set's result.
   bool has_phi_uses () const;
 
+  // If there is exactly one nondebug use of the set's result, return that use,
+  // otherwise return null.  The use might be in an instruction or in a phi
+  // node.
+  use_info *single_nondebug_use () const;
+
+  // If exactly one nondebug instruction uses the set's result, return the use
+  // by that instruction, otherwise return null.
+  use_info *single_nondebug_insn_use () const;
+
+  // If exactly one phi node uses the set's result, return the use by that phi
+  // node, otherwise return null.
+  use_info *single_phi_use () const;
+
   // Return true if the set and its uses are contained within a single
   // extended basic block, with the set coming first.  This implies
   // that all uses are by instructions rather than phi nodes.
diff --git a/gcc/rtl-ssa/member-fns.inl b/gcc/rtl-ssa/member-fns.inl
index e1ab7d1..0b821ae 100644
--- a/gcc/rtl-ssa/member-fns.inl
+++ b/gcc/rtl-ssa/member-fns.inl
@@ -250,6 +250,34 @@ set_info::has_phi_uses () const
   return m_first_use && m_first_use->last_use ()->is_in_phi ();
 }
 
+inline use_info *
+set_info::single_nondebug_use () const
+{
+  if (!has_phi_uses ())
+    return single_nondebug_insn_use ();
+  if (!has_nondebug_insn_uses ())
+    return single_phi_use ();
+  return nullptr;
+}
+
+inline use_info *
+set_info::single_nondebug_insn_use () const
+{
+  use_info *first = first_nondebug_insn_use ();
+  if (first && !first->next_nondebug_insn_use ())
+    return first;
+  return nullptr;
+}
+
+inline use_info *
+set_info::single_phi_use () const
+{
+  use_info *last = last_phi_use ();
+  if (last && !last->prev_phi_use ())
+    return last;
+  return nullptr;
+}
+
 inline bool
 set_info::is_local_to_ebb () const
 {
diff --git a/gcc/testsuite/gcc.target/s390/vector/long-double-asm-abi.c b/gcc/testsuite/gcc.target/s390/vector/long-double-asm-abi.c
new file mode 100644
index 0000000..f9f2d12
--- /dev/null
+++ b/gcc/testsuite/gcc.target/s390/vector/long-double-asm-abi.c
@@ -0,0 +1,26 @@
+/* { dg-do compile } */
+/* { dg-options "-O3 -march=z14 -mzarch --save-temps" } */
+/* { dg-do run { target { s390_z14_hw } } } */
+#include <assert.h>
+#include <stdint.h>
+
+__attribute__ ((noipa)) static long double
+xsqrt (long double x)
+{
+  long double res;
+  asm("sqxbr\t%0,%1" : "=f"(res) : "f"(x));
+  return res;
+}
+
+/* Check that the generated code is very small and straightforward.  In
+   particular, there must be no unnecessary copying and no stack frame.  */
+/* { dg-final { scan-assembler {\n\tld\t[^\n]*\n\tld\t[^\n]*\n(#[^\n]*\n)*\tsqxbr\t.*\n(#[^\n]*\n)*\tstd\t[^\n]*\n\tstd\t[^\n]*\n\tbr\t%r14\n} } } */
+
+int
+main (void)
+{
+  long double res, x = 0x1.0000000000001p+0L,
+		   exp = 1.00000000000000011102230246251564788e+0L;
+  res = xsqrt (x);
+  assert (res == exp);
+}