| Message ID | 20240711121208.45328-1-syq@gcc.gnu.org |
|---|---|
| State | New |
| Headers | show |
| Series | [1/2] Add allow_uninitialized to tree_base.u.bits for VAR_DECL | expand |
On Thu, Jul 11, 2024 at 2:14 PM YunQiang Su <syq@gcc.gnu.org> wrote: > > From: YunQiang Su <yunqiang@isrc.iscas.ac.cn> > > Uninitialized internal temp variable may be useful in some case, > such as for COND_LEN_MUL etc on RISC-V with V extension: If an > const or pre-exists VAR is used, we have to use "undisturbed" > policy; if an uninitialized VAR is used, we can use "agnostic". > With "agnostic", the microarchitectures can omit copying part of > the VAR. No please, there's TREE_NO_WARNING already. > gcc > * tree-core.h(tree_base): Add u.bits.allow_uninitialized. > * tree.h: Add new macro TREE_ALLOW_UNINITIALIZED. > * tree-ssa-uninit.cc(warn_uninit): Don't warn if VAR is > marked as allow_uninitialized. > --- > gcc/tree-core.h | 5 ++++- > gcc/tree-ssa-uninit.cc | 4 ++++ > gcc/tree.h | 4 ++++ > 3 files changed, 12 insertions(+), 1 deletion(-) > > diff --git a/gcc/tree-core.h b/gcc/tree-core.h > index 27c569c7702..984201199f6 100644 > --- a/gcc/tree-core.h > +++ b/gcc/tree-core.h > @@ -1101,7 +1101,10 @@ struct GTY(()) tree_base { > unsigned nameless_flag : 1; > unsigned atomic_flag : 1; > unsigned unavailable_flag : 1; > - unsigned spare0 : 2; > + /* Don't warn if uninitialized. RISC-V V has tail agnostic/undisturbed > + policy, which may be get benifits if we use an uninitialized var. */ > + unsigned allow_uninitialized : 1; > + unsigned spare0 : 1; > > unsigned spare1 : 8; > > diff --git a/gcc/tree-ssa-uninit.cc b/gcc/tree-ssa-uninit.cc > index 726684e472a..12861e1dbc9 100644 > --- a/gcc/tree-ssa-uninit.cc > +++ b/gcc/tree-ssa-uninit.cc > @@ -142,6 +142,10 @@ warn_uninit (opt_code opt, tree t, tree var, gimple *context, > if (!has_undefined_value_p (t)) > return; > > + /* VAR may mark itself as allow_uninitialized. */ > + if (TREE_ALLOW_UNINITIALIZED (var)) > + return; > + > /* Ignore COMPLEX_EXPR as initializing only a part of a complex > turns in a COMPLEX_EXPR with the not initialized part being > set to its previous (undefined) value. */ > diff --git a/gcc/tree.h b/gcc/tree.h > index 28e8e71b036..381780fde2e 100644 > --- a/gcc/tree.h > +++ b/gcc/tree.h > @@ -3311,6 +3311,10 @@ extern void decl_fini_priority_insert (tree, priority_type); > #define VAR_DECL_IS_VIRTUAL_OPERAND(NODE) \ > (VAR_DECL_CHECK (NODE)->base.u.bits.saturating_flag) > > +/* In a VAR_DECL, nonzero if NODE is allowed to be uninitialized. */ > +#define TREE_ALLOW_UNINITIALIZED(NODE) \ > + (VAR_DECL_CHECK (NODE)->base.u.bits.allow_uninitialized) > + > /* In a VAR_DECL, nonzero if this is a non-local frame structure. */ > #define DECL_NONLOCAL_FRAME(NODE) \ > (VAR_DECL_CHECK (NODE)->base.default_def_flag) > -- > 2.45.1 >
diff --git a/gcc/tree-core.h b/gcc/tree-core.h index 27c569c7702..984201199f6 100644 --- a/gcc/tree-core.h +++ b/gcc/tree-core.h @@ -1101,7 +1101,10 @@ struct GTY(()) tree_base { unsigned nameless_flag : 1; unsigned atomic_flag : 1; unsigned unavailable_flag : 1; - unsigned spare0 : 2; + /* Don't warn if uninitialized. RISC-V V has tail agnostic/undisturbed + policy, which may be get benifits if we use an uninitialized var. */ + unsigned allow_uninitialized : 1; + unsigned spare0 : 1; unsigned spare1 : 8; diff --git a/gcc/tree-ssa-uninit.cc b/gcc/tree-ssa-uninit.cc index 726684e472a..12861e1dbc9 100644 --- a/gcc/tree-ssa-uninit.cc +++ b/gcc/tree-ssa-uninit.cc @@ -142,6 +142,10 @@ warn_uninit (opt_code opt, tree t, tree var, gimple *context, if (!has_undefined_value_p (t)) return; + /* VAR may mark itself as allow_uninitialized. */ + if (TREE_ALLOW_UNINITIALIZED (var)) + return; + /* Ignore COMPLEX_EXPR as initializing only a part of a complex turns in a COMPLEX_EXPR with the not initialized part being set to its previous (undefined) value. */ diff --git a/gcc/tree.h b/gcc/tree.h index 28e8e71b036..381780fde2e 100644 --- a/gcc/tree.h +++ b/gcc/tree.h @@ -3311,6 +3311,10 @@ extern void decl_fini_priority_insert (tree, priority_type); #define VAR_DECL_IS_VIRTUAL_OPERAND(NODE) \ (VAR_DECL_CHECK (NODE)->base.u.bits.saturating_flag) +/* In a VAR_DECL, nonzero if NODE is allowed to be uninitialized. */ +#define TREE_ALLOW_UNINITIALIZED(NODE) \ + (VAR_DECL_CHECK (NODE)->base.u.bits.allow_uninitialized) + /* In a VAR_DECL, nonzero if this is a non-local frame structure. */ #define DECL_NONLOCAL_FRAME(NODE) \ (VAR_DECL_CHECK (NODE)->base.default_def_flag)
From: YunQiang Su <yunqiang@isrc.iscas.ac.cn> Uninitialized internal temp variable may be useful in some case, such as for COND_LEN_MUL etc on RISC-V with V extension: If an const or pre-exists VAR is used, we have to use "undisturbed" policy; if an uninitialized VAR is used, we can use "agnostic". With "agnostic", the microarchitectures can omit copying part of the VAR. gcc * tree-core.h(tree_base): Add u.bits.allow_uninitialized. * tree.h: Add new macro TREE_ALLOW_UNINITIALIZED. * tree-ssa-uninit.cc(warn_uninit): Don't warn if VAR is marked as allow_uninitialized. --- gcc/tree-core.h | 5 ++++- gcc/tree-ssa-uninit.cc | 4 ++++ gcc/tree.h | 4 ++++ 3 files changed, 12 insertions(+), 1 deletion(-)