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 --git a/gcc/testsuite/gcc.c-torture/compile/pr110271.c b/gcc/testsuite/gcc.c-torture/compile/pr110271.c
new file mode 100644 (file)
index 0000000..0cb91be
--- /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 b2764d4bfc14621e8fb4fc2295bc9601190015bd..d2b71295f965dd8addf4e7fff692a7e8a42fa669 100644 (file)
--- 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: