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Shorten right-shift again in C++.

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Back in SVN r131862 richi removed this code to fix PR 34235, but didn't
remove the parallel code from the C front-end because the bug had previously
been fixed in r44080.  This patch copies the code from C again.

	* typeck.c (cp_build_binary_op): Restore short_shift code.

From-SVN: r280128
This commit is contained in:
Jason Merrill 2020-01-10 13:53:17 -05:00 committed by Jason Merrill
parent e0804c9b5e
commit 337ea6b216
2 changed files with 40 additions and 0 deletions
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2
gcc/cp/ChangeLog
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@ -1,5 +1,7 @@
2020-01-10 Jason Merrill <jason@redhat.com>
* typeck.c (cp_build_binary_op): Restore short_shift code.
PR c++/93143 - incorrect tree sharing with constexpr.
* constexpr.c (cxx_eval_outermost_constant_expr): Don't assume
CONSTRUCTORs are already unshared.

38
gcc/cp/typeck.c
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@ -4452,6 +4452,10 @@ cp_build_binary_op (const op_location_t &location,
Also implies COMMON. */
int short_compare = 0;
/* Nonzero if this is a right-shift operation, which can be computed on the
original short and then promoted if the operand is a promoted short. */
int short_shift = 0;
/* Nonzero means set RESULT_TYPE to the common type of the args. */
int common = 0;
@ -4844,6 +4848,9 @@ cp_build_binary_op (const op_location_t &location,
}
else
{
if (!integer_zerop (op1))
short_shift = 1;
if (compare_tree_int (const_op1, TYPE_PRECISION (type0)) >= 0
&& (complain & tf_warning)
&& c_inhibit_evaluation_warnings == 0)
@ -5586,6 +5593,37 @@ cp_build_binary_op (const op_location_t &location,
shorten == -1);
}
/* Shifts can be shortened if shifting right. */
if (short_shift)
{
int unsigned_arg;
tree arg0 = get_narrower (op0, &unsigned_arg);
final_type = result_type;
if (arg0 == op0 && final_type == TREE_TYPE (op0))
unsigned_arg = TYPE_UNSIGNED (TREE_TYPE (op0));
if (TYPE_PRECISION (TREE_TYPE (arg0)) < TYPE_PRECISION (result_type)
&& tree_int_cst_sgn (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
/* We cannot drop an unsigned shift after sign-extension. */
&& (!TYPE_UNSIGNED (final_type) || unsigned_arg))
{
/* Do an unsigned shift if the operand was zero-extended. */
result_type
= c_common_signed_or_unsigned_type (unsigned_arg,
TREE_TYPE (arg0));
/* Convert value-to-be-shifted to that type. */
if (TREE_TYPE (op0) != result_type)
op0 = convert (result_type, op0);
converted = 1;
}
}
/* Comparison operations are shortened too but differently.
They identify themselves by setting short_compare = 1. */