[committed] widening_mul: Fix up signed multiplication overflow check handling [PR98727]

[Jakub Jelinek]

Hi!

I forgot one line, which means that if the second operand of the multiplication
isn't constant, it would be just the same as the first one.

Fixed thusly, bootstrapped/regtested on x86_64-linux and i686-linux,
committed as obvious to trunk.

2021-01-18  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/98727
	* tree-ssa-math-opts.c (match_arith_overflow): Fix up computation of
	second .MUL_OVERFLOW operand for signed multiplication with overflow
	checking if the second operand of multiplication is not constant.

	* gcc.c-torture/execute/pr98727.c: New test.

--- gcc/tree-ssa-math-opts.c.jj	2021-01-12 11:04:39.000000000 +0100
+++ gcc/tree-ssa-math-opts.c	2021-01-18 13:36:38.707210300 +0100
@@ -4170,6 +4170,7 @@ match_arith_overflow (gimple_stmt_iterat
 	rhs2 = fold_convert (type, rhs2);
       else
 	{
+	  g = SSA_NAME_DEF_STMT (rhs2);
 	  if (gimple_assign_cast_p (g)
 	      && useless_type_conversion_p (type,
 					    TREE_TYPE (gimple_assign_rhs1 (g)))
--- gcc/testsuite/gcc.c-torture/execute/pr98727.c.jj	2021-01-18 13:47:00.227192663 +0100
+++ gcc/testsuite/gcc.c-torture/execute/pr98727.c	2021-01-18 13:46:29.511539475 +0100
@@ -0,0 +1,20 @@
+/* PR tree-optimization/98727 */
+
+__attribute__((noipa)) long int
+foo (long int x, long int y)
+{
+  long int z = (unsigned long) x * y;
+  if (x != z / y)
+    return -1;
+  return z;
+}
+
+int
+main ()
+{
+  if (foo (4, 24) != 96
+      || foo (124, 126) != 124L * 126
+      || foo (__LONG_MAX__ / 16, 17) != -1)
+    __builtin_abort ();
+  return 0;
+}


	Jakub