re PR tree-optimization/37242 (missed FRE opportunity because of signedness of addition)

2019-08-20  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/37242
	* tree-ssa-sccvn.c (visit_nary_op): Also CSE (T)(a + b)
	to (T)a + (T)b if we know that a + b does not overflow.

	* gcc.dg/tree-ssa/ssa-fre-80.c: New testcase.

From-SVN: r274746

gcc/ChangeLog

+2019-08-20  Richard Biener  <rguenther@suse.de>
+
+	PR tree-optimization/37242
+	* tree-ssa-sccvn.c (visit_nary_op): Also CSE (T)(a + b)
+	to (T)a + (T)b if we know that a + b does not overflow.
+
 2019-08-20  Eric Botcazou  <ebotcazou@adacore.com>
 
 	PR rtl-optimization/91347

gcc/testsuite/ChangeLog

+2019-08-20  Richard Biener  <rguenther@suse.de>
+
+	PR tree-optimization/37242
+	* gcc.dg/tree-ssa/ssa-fre-80.c: New testcase.
+
 2019-08-20  Ed Schonberg  <schonberg@adacore.com>
 
 	* gnat.dg/storage_size1.adb: New testcase.

gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-80.c

+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-fre1" } */
+
+unsigned long a, b;
+void foo (int m, int f)
+{
+  unsigned long tem = (unsigned long)m;
+  a = tem + 1;
+  if (f)
+    {
+      int tem2 = m + 1;
+      b = (unsigned long)tem2;  /* Eliminated to a.  */
+    }
+}
+
+/* { dg-final { scan-tree-dump-times "\\(long unsigned int\\)" 1 "fre1" } } */

gcc/tree-ssa-sccvn.c

@@ -4312,8 +4312,12 @@ visit_nary_op (tree lhs, gassign *stmt)
 	 operation.  */
       if (INTEGRAL_TYPE_P (type)
 	  && TREE_CODE (rhs1) == SSA_NAME
-	  /* We only handle sign-changes or zero-extension -> & mask.  */
-	  && ((TYPE_UNSIGNED (TREE_TYPE (rhs1))
+	  /* We only handle sign-changes, zero-extension -> & mask or
+	     sign-extension if we know the inner operation doesn't
+	     overflow.  */
+	  && (((TYPE_UNSIGNED (TREE_TYPE (rhs1))
+		|| (INTEGRAL_TYPE_P (TREE_TYPE (rhs1))
+		    && TYPE_OVERFLOW_UNDEFINED (TREE_TYPE (rhs1))))
 	       && TYPE_PRECISION (type) > TYPE_PRECISION (TREE_TYPE (rhs1)))
 	      || TYPE_PRECISION (type) == TYPE_PRECISION (TREE_TYPE (rhs1))))
 	{
@@ -4347,7 +4351,9 @@ visit_nary_op (tree lhs, gassign *stmt)
 		    {
 		      unsigned lhs_prec = TYPE_PRECISION (type);
 		      unsigned rhs_prec = TYPE_PRECISION (TREE_TYPE (rhs1));
-		      if (lhs_prec == rhs_prec)
+		      if (lhs_prec == rhs_prec
+			  || (INTEGRAL_TYPE_P (TREE_TYPE (rhs1))
+			      && TYPE_OVERFLOW_UNDEFINED (TREE_TYPE (rhs1))))
 			{
 			  gimple_match_op match_op (gimple_match_cond::UNCOND,
 						    NOP_EXPR, type, ops[0]);