Hi,
Due to the way bit-field access lower is done, we can get an
unitialized memory load and this causes the unitialized warning to
kick in.
The case we have is:
temp_1 = BIT_FIELD_REF<a, 0, 64>
temp_2 = BIT_INSERT<temp_1, V, P (N bits)>
BIT_FIELD_REF<a, 0, 64> = temp_2
What this patch does is similar to what was done for the case of
BIT_INSERT for unitialized ssa names (default) but for memory
accesses.
Note also tested with the bit-field lower pass added; this and the
fold-const.c/tree-ssa-sccvn.c patch (which was just committed) are
requirements to the lower pass.
OK? Bootstrapped and tested on aarch64-linux-gnu with no regressions.
Thanks,
Andrew Pinski
* tree-ssa-uninit.c (warn_uninitialized_vars): Don't warn about memory
accesses where the use is for the first operand of a BIT_INSERT.
Index: tree-ssa-uninit.c
===================================================================
--- tree-ssa-uninit.c (revision 250430)
+++ tree-ssa-uninit.c (working copy)
@@ -273,6 +273,11 @@ warn_uninitialized_vars (bool warn_possi
&& gimple_has_location (stmt))
{
tree rhs = gimple_assign_rhs1 (stmt);
+ tree lhs = gimple_assign_lhs (stmt);
+ bool has_bit_insert = false;
+ use_operand_p luse_p;
+ imm_use_iterator liter;
+
if (TREE_NO_WARNING (rhs))
continue;
@@ -300,6 +305,26 @@ warn_uninitialized_vars (bool warn_possi
ref.offset) <= 0)))
continue;
+ /* Do not warn if the access is then used for a BIT_INSERT_EXPR.
*/
+ if (TREE_CODE (lhs) == SSA_NAME)
+ FOR_EACH_IMM_USE_FAST (luse_p, liter, lhs)
+ {
+ gimple *use_stmt = USE_STMT (luse_p);
+ /* BIT_INSERT_EXPR first operand should not be considered
+ a use for the purpose of uninit warnings. */
+ if (gassign *ass = dyn_cast <gassign *> (use_stmt))
+ {
+ if (gimple_assign_rhs_code (ass) == BIT_INSERT_EXPR
+ && luse_p->use == gimple_assign_rhs1_ptr (ass))
+ {
+ has_bit_insert = true;
+ break;
+ }
+ }
+ }
+ if (has_bit_insert)
+ continue;
+
/* Limit the walking to a constant number of stmts after
we overcommit quadratic behavior for small functions
and O(n) behavior. */
