don't try to compute it in the compiler. */
if (TREE_CODE (arg1) == INTEGER_CST && tree_int_cst_sgn (arg1) < 0)
return NULL_TREE;
+
+ /* Turn (a OP c1) OP c2 into a OP (c1+c2). */
+ if (TREE_CODE (arg0) == code && host_integerp (arg1, false)
+ && TREE_INT_CST_LOW (arg1) < TYPE_PRECISION (type)
+ && host_integerp (TREE_OPERAND (arg0, 1), false)
+ && TREE_INT_CST_LOW (TREE_OPERAND (arg0, 1)) < TYPE_PRECISION (type))
+ {
+ HOST_WIDE_INT low = (TREE_INT_CST_LOW (TREE_OPERAND (arg0, 1))
+ + TREE_INT_CST_LOW (arg1));
+
+ /* Deal with a OP (c1 + c2) being undefined but (a OP c1) OP c2
+ being well defined. */
+ if (low >= TYPE_PRECISION (type))
+ {
+ if (code == LROTATE_EXPR || code == RROTATE_EXPR)
+ low = low % TYPE_PRECISION (type);
+ else if (TYPE_UNSIGNED (type) || code == LSHIFT_EXPR)
+ return build_int_cst (type, 0);
+ else
+ low = TYPE_PRECISION (type) - 1;
+ }
+
+ return fold_build2 (code, type, TREE_OPERAND (arg0, 0),
+ build_int_cst (type, low));
+ }
+
+ /* Transform (x >> c) << c into x & (-1<<c) */
+ if (code == LSHIFT_EXPR && TREE_CODE (arg0) == RSHIFT_EXPR
+ && host_integerp (arg1, false)
+ && TREE_INT_CST_LOW (arg1) < TYPE_PRECISION (type)
+ && host_integerp (TREE_OPERAND (arg0, 1), false)
+ && TREE_INT_CST_LOW (TREE_OPERAND (arg0, 1)) < TYPE_PRECISION (type))
+ {
+ HOST_WIDE_INT low0 = TREE_INT_CST_LOW (TREE_OPERAND (arg0, 1));
+ HOST_WIDE_INT low1 = TREE_INT_CST_LOW (arg1);
+ unsigned HOST_WIDE_INT low;
+ HOST_WIDE_INT high;
+ tree lshift;
+ tree arg00;
+
+ if (low0 == low1)
+ {
+ arg00 = fold_convert (type, TREE_OPERAND (arg0, 0));
+
+ lshift_double (-1, -1, low0 < low1 ? low0 : low1,
+ TYPE_PRECISION (type), &low, &high, 1);
+ lshift = build_int_cst_wide (type, low, high);
+
+ return fold_build2 (BIT_AND_EXPR, type, arg00, lshift);
+ }
+ }
+
+
/* Rewrite an LROTATE_EXPR by a constant into an
RROTATE_EXPR by a new constant. */
if (code == LROTATE_EXPR && TREE_CODE (arg1) == INTEGER_CST)
--- /dev/null
+/* { dg-do compile } */
+/* { dg-options "-fdump-tree-gimple" } */
+
+int f (int a) {
+ return (a << 31) << 6;
+}
+
+unsigned int g (unsigned int a) {
+ return (a >> 7) >> 25;
+}
+
+int h (int b) {
+ return (b >> 30) >> 30;
+}
+
+long long j (long long c) {
+ return (c >> 35) << 35;
+}
+/* { dg-final { scan-tree-dump-times "= 0" 2 "gimple" } } */
+/* { dg-final { scan-tree-dump "b >> 31" "gimple" } } */
+/* { dg-final { scan-tree-dump "c & -34359738368" "gimple" } } */
+/* { dg-final { cleanup-tree-dump "gimple" } } */