[gcc/devel/c++-modules] PR c++/93238 - short right-shift with enum.

[Nathan Sidwell]

https://gcc.gnu.org/g:f1acad4e43908e90ca2b5155a878639cbea4c4e1

commit f1acad4e43908e90ca2b5155a878639cbea4c4e1
Author: Jason Merrill <jason@redhat.com>
Date:   Sun Jan 12 15:09:22 2020 -0500

    	PR c++/93238 - short right-shift with enum.
    
    My earlier patch to reintroduce short_shift failed to adjust for the C++
    front end use of const_op1 rather than op1.
    
    	* typeck.c (cp_build_binary_op): Use folded op1 for short_shift.

Diff:
---
 gcc/cp/ChangeLog                    | 5 +++++
 gcc/cp/typeck.c                     | 8 +++++---
 gcc/testsuite/g++.dg/expr/rshift1.C | 8 ++++++++
 3 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index 1dad238..9b226b8 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,8 @@
+2020-01-13  Jason Merrill  <jason@redhat.com>
+
+	PR c++/93238 - short right-shift with enum.
+	* typeck.c (cp_build_binary_op): Use folded op1 for short_shift.
+
 2020-01-10  Jason Merrill  <jason@redhat.com>
 
 	* typeck.c (cp_build_binary_op): Restore short_shift code.
diff --git a/gcc/cp/typeck.c b/gcc/cp/typeck.c
index 7b653ceb..8955442 100644
--- a/gcc/cp/typeck.c
+++ b/gcc/cp/typeck.c
@@ -4848,7 +4848,7 @@ cp_build_binary_op (const op_location_t &location,
 		}
 	      else
 		{
-		  if (!integer_zerop (op1))
+		  if (!integer_zerop (const_op1))
 		    short_shift = 1;
 
 		  if (compare_tree_int (const_op1, TYPE_PRECISION (type0)) >= 0
@@ -5599,6 +5599,7 @@ cp_build_binary_op (const op_location_t &location,
 	{
 	  int unsigned_arg;
 	  tree arg0 = get_narrower (op0, &unsigned_arg);
+	  tree const_op1 = cp_fold_rvalue (op1);
 
 	  final_type = result_type;
 
@@ -5606,10 +5607,11 @@ cp_build_binary_op (const op_location_t &location,
 	    unsigned_arg = TYPE_UNSIGNED (TREE_TYPE (op0));
 
 	  if (TYPE_PRECISION (TREE_TYPE (arg0)) < TYPE_PRECISION (result_type)
-	      && tree_int_cst_sgn (op1) > 0
+	      && tree_int_cst_sgn (const_op1) > 0
 	      /* We can shorten only if the shift count is less than the
 		 number of bits in the smaller type size.  */
-	      && compare_tree_int (op1, TYPE_PRECISION (TREE_TYPE (arg0))) < 0
+	      && compare_tree_int (const_op1,
+				   TYPE_PRECISION (TREE_TYPE (arg0))) < 0
 	      /* We cannot drop an unsigned shift after sign-extension.  */
 	      && (!TYPE_UNSIGNED (final_type) || unsigned_arg))
 	    {
diff --git a/gcc/testsuite/g++.dg/expr/rshift1.C b/gcc/testsuite/g++.dg/expr/rshift1.C
new file mode 100644
index 0000000..2f81c02
--- /dev/null
+++ b/gcc/testsuite/g++.dg/expr/rshift1.C
@@ -0,0 +1,8 @@
+// PR c++/93238
+
+short s;
+enum { zero };
+int fn(int i)
+{
+  return s >> zero;
+}