From: YunQiang Su <[email protected]>
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(-)
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
