[PATCH] Fix PR88301

[Richard Biener <rguenther@suse.de>]

This fixes a missed optimization in EVRP by teaching the code
figuring out conditional asserts about conversions that preserve
the converted value.

Bootstrapped and tested on x86_64-unknown-linux-gnu, applied to trunk 
sofar.

Richard.

2018-12-03  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/88301
	* tree-vrp.c (register_edge_assert_for_2): Handle conversions
	that do not change the value by registering the same assert
	for the operand.

	* gcc.dg/tree-ssa/evrp13.c: New testcase.

Index: gcc/tree-vrp.c
===================================================================
--- gcc/tree-vrp.c	(revision 266733)
+++ gcc/tree-vrp.c	(working copy)
@@ -2966,6 +2966,23 @@ register_edge_assert_for_2 (tree name, e
 	    add_assert_info (asserts, name2, tmp, new_comp_code, new_val);
 	}
 
+      /* If we have a conversion that doesn't change the value of the source
+         simply register the same assert for it.  */
+      if (CONVERT_EXPR_CODE_P (rhs_code))
+	{
+	  wide_int rmin, rmax;
+	  tree rhs1 = gimple_assign_rhs1 (def_stmt);
+	  if (INTEGRAL_TYPE_P (TREE_TYPE (rhs1))
+	      && int_fits_type_p (val, TREE_TYPE (rhs1))
+	      && ((TYPE_PRECISION (TREE_TYPE (name))
+		   > TYPE_PRECISION (TREE_TYPE (rhs1)))
+		  || (get_range_info (rhs1, &rmin, &rmax) == VR_RANGE
+		      && wi::fits_to_tree_p (rmin, TREE_TYPE (name))
+		      && wi::fits_to_tree_p (rmax, TREE_TYPE (name)))))
+	    add_assert_info (asserts, rhs1, rhs1,
+		 	     comp_code, fold_convert (TREE_TYPE (rhs1), val));
+	}
+
       /* Add asserts for NAME cmp CST and NAME being defined as
 	 NAME = NAME2 & CST2.
 
Index: gcc/testsuite/gcc.dg/tree-ssa/evrp13.c
===================================================================
--- gcc/testsuite/gcc.dg/tree-ssa/evrp13.c	(revision 0)
+++ gcc/testsuite/gcc.dg/tree-ssa/evrp13.c	(working copy)
@@ -0,0 +1,7 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-evrp" } */
+
+#define ADD_NW(A,B) (__extension__({ __typeof(A+B) R; if(__builtin_add_overflow(A,B,&R)) __builtin_unreachable(); R ;}))
+_Bool a_b2(unsigned A,  unsigned B) { return ADD_NW(A,B) >= B; }
+
+/* { dg-final { scan-tree-dump "return 1;" "evrp" } } */