[RFC] Add gcc_assert_implies
[ Following up on "Fix bug in simplify_ternary_operation" (
https://gcc.gnu.org/ml/gcc-patches/2017-11/msg01699.html ). ]
The C/C++ languages do not support the implication logical operator a -> b, so
we typically use '!a || b'. Or, possibly the equivalent but more complicated
'!(a && !b)'. Both have the convenient property that b is not evaluated if !a.
However, for both forms, the more complex and/or long operands a and b become,
the harder it becomes to understand that there's an implication relationship.
Add a macro gcc_assert_implies(a, b) that allows us to express a top-level
implication relationship in an assert.
The semantics of gcc_assert_implies (a, b) can understood as:
...
if (a)
gcc_assert (b);
...
[ So an alternative name could be gcc_assert_if, gcc_if_assert or
gcc_cond_assert. ]
Also, using this kind of assert will make it easier to spot that:
...
gcc_assert_implies (a, b);
if (a)
{
...
}
...
can be simplified into:
...
if (a)
{
gcc_assert (b);
...
}
...
2019-01-06 Tom de Vries <tdevries@suse.de>
* system.h (gcc_assert_implies): Define.
* gimple-iterator.c (gsi_insert_seq_nodes_before): Use
gcc_assert_implies.
* simplify-rtx.c (simplify_const_relational_operation): Same.
---
gcc/gimple-iterator.c | 2 +-
gcc/simplify-rtx.c | 5 ++---
gcc/system.h | 2 ++
3 files changed, 5 insertions(+), 4 deletions(-)
@@ -119,7 +119,7 @@ gsi_insert_seq_nodes_before (gimple_stmt_iterator *i,
basic_block bb;
gimple_seq_node cur = i->ptr;
- gcc_assert (!cur || cur->prev);
+ gcc_assert_implies (cur, cur->prev);
if ((bb = gsi_bb (*i)) != NULL)
update_bb_for_stmts (first, last, bb);
@@ -5234,9 +5234,8 @@ simplify_const_relational_operation (enum rtx_code code,
rtx trueop0;
rtx trueop1;
- gcc_assert (mode != VOIDmode
- || (GET_MODE (op0) == VOIDmode
- && GET_MODE (op1) == VOIDmode));
+ gcc_assert_implies (mode == VOIDmode,
+ GET_MODE (op0) == VOIDmode && GET_MODE (op1) == VOIDmode);
/* If op0 is a compare, extract the comparison arguments from it. */
if (GET_CODE (op0) == COMPARE && op1 == const0_rtx)
@@ -748,6 +748,8 @@ extern void fancy_abort (const char *, int, const char *)
#define gcc_assert(EXPR) ((void)(0 && (EXPR)))
#endif
+#define gcc_assert_implies(EXPR1, EXPR2) gcc_assert (!(EXPR1) || (EXPR2))
+
#if CHECKING_P
#define gcc_checking_assert(EXPR) gcc_assert (EXPR)
#else