re PR tree-optimization/56899 (Wrong constant folding)

	PR tree-optimization/56899
	* fold-const.c (extract_muldiv_1): Apply distributive law
	only if TYPE_OVERFLOW_WRAPS (ctype).

	* gcc.c-torture/execute/pr56899.c: New test.

From-SVN: r197692

4 files changed, 62 insertions, 2 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 7e1cc32..bab67ab 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,9 @@
+2013-04-11  Jakub Jelinek  <jakub@redhat.com>
+
+	PR tree-optimization/56899
+	* fold-const.c (extract_muldiv_1): Apply distributive law
+	only if TYPE_OVERFLOW_WRAPS (ctype).
+
 2013-04-11  Bin Cheng  <bin.cheng@arm.com>
 
 	PR target/56124
diff --git a/gcc/fold-const.c b/gcc/fold-const.c
index dcf7aa0..467b6d6 100644
--- a/gcc/fold-const.c
+++ b/gcc/fold-const.c
@@ -5850,8 +5850,10 @@ extract_muldiv_1 (tree t, tree c, enum tree_code code, tree wide_type,
 
       /* The last case is if we are a multiply.  In that case, we can
 	 apply the distributive law to commute the multiply and addition
-	 if the multiplication of the constants doesn't overflow.  */
-      if (code == MULT_EXPR)
+	 if the multiplication of the constants doesn't overflow
+	 and overflow is defined.  With undefined overflow
+	 op0 * c might overflow, while (op0 + orig_op1) * c doesn't.  */
+      if (code == MULT_EXPR && TYPE_OVERFLOW_WRAPS (ctype))
 	return fold_build2 (tcode, ctype,
 			    fold_build2 (code, ctype,
 					 fold_convert (ctype, op0),
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index ef84fe1..6255702 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2013-04-11  Jakub Jelinek  <jakub@redhat.com>
+
+	PR tree-optimization/56899
+	* gcc.c-torture/execute/pr56899.c: New test.
+
 2013-04-10  David S. Miller  <davem@davemloft.net>
 
 	* gcc.target/sparc/setcc-4.c: New test.
diff --git a/gcc/testsuite/gcc.c-torture/execute/pr56899.c b/gcc/testsuite/gcc.c-torture/execute/pr56899.c
new file mode 100644
index 0000000..9adf9af
--- /dev/null
+++ b/gcc/testsuite/gcc.c-torture/execute/pr56899.c
@@ -0,0 +1,47 @@
+/* PR tree-optimization/56899 */
+
+#if __SIZEOF_INT__ == 4 && __CHAR_BIT__ == 8
+__attribute__((noinline, noclone)) void
+f1 (int v)
+{
+  int x = -214748365 * (v - 1);
+  if (x != -1932735285)
+    __builtin_abort ();
+}
+
+__attribute__((noinline, noclone)) void
+f2 (int v)
+{
+  int x = 214748365 * (v + 1);
+  if (x != -1932735285)
+    __builtin_abort ();
+}
+
+__attribute__((noinline, noclone)) void
+f3 (unsigned int v)
+{
+  unsigned int x = -214748365U * (v - 1);
+  if (x != -1932735285U)
+    __builtin_abort ();
+}
+
+__attribute__((noinline, noclone)) void
+f4 (unsigned int v)
+{
+  unsigned int x = 214748365U * (v + 1);
+  if (x != -1932735285U)
+    __builtin_abort ();
+}
+#endif
+
+int
+main ()
+{
+#if __SIZEOF_INT__ == 4 && __CHAR_BIT__ == 8
+  f1 (10);
+  f2 (-10);
+  f3 (10);
+  f4 (-10U);
+#endif
+  return 0;
+}