[gcc r14-1895] tree-ssa-math-opts: Fix up uaddc/usubc pattern matching [PR110271]

[gcc r14-1895] tree-ssa-math-opts: Fix up uaddc/usubc pattern matching [PR110271]

[Jakub Jelinek]

https://gcc.gnu.org/g:5b67116a85298bbe358b036d34ad23119cebbdac

commit r14-1895-g5b67116a85298bbe358b036d34ad23119cebbdac
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Fri Jun 16 19:46:36 2023 +0200

    tree-ssa-math-opts: Fix up uaddc/usubc pattern matching [PR110271]
    
    The following testcase ICEs, because I misremembered what the return value
    from match_arith_overflow is.  It isn't true if __builtin_*_overflow was
    matched, but it is true only in the BIT_NOT_EXPR case if stmt was removed.
    
    So, if match_arith_overflow matches something, gsi_stmt (gsi) will not
    be stmt and match_uaddc_usubc will be confused and can ICE.
    
    The following patch fixes it by checking if gsi_stmt (gsi) == stmt,
    in that case we know it is still a PLUS_EXPR/MINUS_EXPR and we can try to
    pattern match it further as UADDC/USUBC.
    
    2023-06-16  Jakub Jelinek  <jakub@redhat.com>
    
            PR tree-optimization/110271
            * tree-ssa-math-opts.cc (math_opts_dom_walker::after_dom_children)
            <case PLUS_EXPR>: Ignore return value from match_arith_overflow,
            instead call match_uaddc_usubc only if gsi_stmt (gsi) is still stmt.
    
            * gcc.c-torture/compile/pr110271.c: New test.

Diff:
---
 gcc/testsuite/gcc.c-torture/compile/pr110271.c | 24 ++++++++++++++++++++++++
 gcc/tree-ssa-math-opts.cc                      |  9 ++++++---
 2 files changed, 30 insertions(+), 3 deletions(-)

diff --git a/gcc/testsuite/gcc.c-torture/compile/pr110271.c b/gcc/testsuite/gcc.c-torture/compile/pr110271.c
new file mode 100644
index 00000000000..0cb91beaaea
--- /dev/null
+++ b/gcc/testsuite/gcc.c-torture/compile/pr110271.c
@@ -0,0 +1,24 @@
+/* PR tree-optimization/110271 */
+
+unsigned a, b, c, d, e;
+
+void
+foo (unsigned *x, int y, unsigned int *z)
+{
+  for (int i = 0; i < y; i++)
+    {
+      b += d;
+      a += b < d;
+      a += c = (__PTRDIFF_TYPE__) x > 3;
+      d = z[1] + (a < c);
+      a += e;
+      d += a < e;
+    }
+}
+
+void
+bar (unsigned int *z)
+{
+  unsigned *x = x;
+  foo (x, 9, z);
+}
diff --git a/gcc/tree-ssa-math-opts.cc b/gcc/tree-ssa-math-opts.cc
index b2764d4bfc1..d2b71295f96 100644
--- a/gcc/tree-ssa-math-opts.cc
+++ b/gcc/tree-ssa-math-opts.cc
@@ -5558,9 +5558,12 @@ math_opts_dom_walker::after_dom_children (basic_block bb)
 
 	    case PLUS_EXPR:
 	    case MINUS_EXPR:
-	      if (!convert_plusminus_to_widen (&gsi, stmt, code)
-		  && !match_arith_overflow (&gsi, stmt, code, m_cfg_changed_p))
-		match_uaddc_usubc (&gsi, stmt, code);
+	      if (!convert_plusminus_to_widen (&gsi, stmt, code))
+		{
+		  match_arith_overflow (&gsi, stmt, code, m_cfg_changed_p);
+		  if (gsi_stmt (gsi) == stmt)
+		    match_uaddc_usubc (&gsi, stmt, code);
+		}
 	      break;
 
 	    case BIT_NOT_EXPR: