https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97588
Martin Jambor <jamborm at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Ever confirmed|0 |1
Status|UNCONFIRMED |NEW
Last reconfirmed| |2021-01-22
--- Comment #2 from Martin Jambor <jamborm at gcc dot gnu.org> ---
SRA only decides to create replacements for the single-bit flags, we
don't do total scalarization when there are bit-fields. Part of the
problem, is that SRA sees some accesses to the flags directly:
flags.flag1 = 1;
but others it does not really see because they are quite indirect:
_13 = BIT_FIELD_REF <flags, 8, 8>;
_14 = _13 & 8;
if (_14 != 0)
...and it still decides to scalarize (more on that below), which means
that it has to store the flag back to flags before the BIT_FIELD_REF,
which leads to impression of the access being split into four parts.
Having said that, scalarizing bit-fields, and even more so 1-bit
flags, when there are not multiple reads from the bit-field itself, is
probably not useful (in the case of non-bit fields it can lead to
disappearance of the aggregate).
So, would the following help the real code that you derived the
testcase from?
diff --git a/gcc/tree-sra.c b/gcc/tree-sra.c
index d177f1ba11c..d3c3a4584a0 100644
--- a/gcc/tree-sra.c
+++ b/gcc/tree-sra.c
@@ -2519,7 +2519,8 @@ analyze_access_subtree (struct access *root, struct
access *parent,
&& (totally || !root->grp_total_scalarization)
&& (totally
|| root->grp_hint
- || ((root->grp_scalar_read || root->grp_assignment_read)
+ || (root->size > 1
+ && (root->grp_scalar_read || root->grp_assignment_read)
&& (root->grp_scalar_write || root->grp_assignment_write))))
{
/* Always create access replacements that cover the whole access.
@@ -2562,11 +2563,10 @@ analyze_access_subtree (struct access *root, struct
access *parent,
&& scalar && !root->first_child
&& !root->grp_total_scalarization
&& (root->grp_scalar_write || root->grp_assignment_write)
+ && (!root->grp_scalar_read && !root->grp_assignment_read)
&& !bitmap_bit_p (cannot_scalarize_away_bitmap,
DECL_UID (root->base)))
{
- gcc_checking_assert (!root->grp_scalar_read
- && !root->grp_assignment_read);
sth_created = true;
if (MAY_HAVE_DEBUG_BIND_STMTS)
{
