Hello,
as my patch for stack-arrays in fortran reveals we a problem that VLA
objects basically prevent all inlining to happen. They're transformed
into alloca calls and those are considered to disable inlining. The
(correct) fear being that inlining a bare alloca call into a loop leads to
unbounded stack growth.
But the situation is different for alloca calls emitted for dealing with
VLA objects. They always are wrapped with stack_save/stack_restore calls.
Inlining such regions always is okay, even into loops. The stack space
usage will be exactly the same at runtime.
We have a flag for this already on the CALL_EXPR. But we don't retain it
over tuples, and hence we also don't look at it in
inline_forbidden_p_stmt. This patch fixes both. (The strange testing of
builtin-ness is because in CALL_EXPR the ALLOCA_FOR_VAR_P and
CALL_FROM_THUNK_P flags are overloaded)
(This fixes the regression of fatigue with the stack-arrays patch)
regstrapping on x86_64-linux in progress, okay for trunk?
Ciao,
Michael.
* gimple.h (enum gf_mask): Add GF_CALL_ALLOCA_FOR_VAR.
(gimple_call_set_alloca_for_var): New inline function.
(gimple_call_alloca_for_var_p): Ditto.
* gimple.c (gimple_build_call_from_tree): Remember ALLOCA_FOR_VAR_P
state.
* cfgexpand.c (expand_call_stmt): Restore ALLOCA_FOR_VAR_P state.
* tree-inline.c (inline_forbidden_p_stmt): Don't reject alloca
calls if they were for VLA objects.
Index: cfgexpand.c
===================================================================
*** cfgexpand.c (revision 172431)
--- cfgexpand.c (working copy)
*************** expand_call_stmt (gimple stmt)
*** 1873,1879 ****
CALL_EXPR_TAILCALL (exp) = gimple_call_tail_p (stmt);
CALL_EXPR_RETURN_SLOT_OPT (exp) = gimple_call_return_slot_opt_p (stmt);
! CALL_FROM_THUNK_P (exp) = gimple_call_from_thunk_p (stmt);
CALL_CANNOT_INLINE_P (exp) = gimple_call_cannot_inline_p (stmt);
CALL_EXPR_VA_ARG_PACK (exp) = gimple_call_va_arg_pack_p (stmt);
SET_EXPR_LOCATION (exp, gimple_location (stmt));
--- 1873,1884 ----
CALL_EXPR_TAILCALL (exp) = gimple_call_tail_p (stmt);
CALL_EXPR_RETURN_SLOT_OPT (exp) = gimple_call_return_slot_opt_p (stmt);
! if (decl
! && DECL_BUILT_IN_CLASS (decl) == BUILT_IN_NORMAL
! && DECL_FUNCTION_CODE (decl) == BUILT_IN_ALLOCA)
! ALLOCA_FOR_VAR_P (exp) = gimple_call_alloca_for_var_p (stmt);
! else
! CALL_FROM_THUNK_P (exp) = gimple_call_from_thunk_p (stmt);
CALL_CANNOT_INLINE_P (exp) = gimple_call_cannot_inline_p (stmt);
CALL_EXPR_VA_ARG_PACK (exp) = gimple_call_va_arg_pack_p (stmt);
SET_EXPR_LOCATION (exp, gimple_location (stmt));
Index: tree-inline.c
===================================================================
*** tree-inline.c (revision 172431)
--- tree-inline.c (working copy)
*************** inline_forbidden_p_stmt (gimple_stmt_ite
*** 2997,3004 ****
this may change program's memory overhead drastically when the
function using alloca is called in loop. In GCC present in
SPEC2000 inlining into schedule_block cause it to require 2GB of
! RAM instead of 256MB. */
if (gimple_alloca_call_p (stmt)
&& !lookup_attribute ("always_inline", DECL_ATTRIBUTES (fn)))
{
inline_forbidden_reason
--- 2997,3007 ----
this may change program's memory overhead drastically when the
function using alloca is called in loop. In GCC present in
SPEC2000 inlining into schedule_block cause it to require 2GB of
! RAM instead of 256MB. Don't do so for alloca calls emitted for
! VLA objects as those can't cause unbounded growth (they're always
! wrapped inside stack_save/stack_restore regions. */
if (gimple_alloca_call_p (stmt)
+ && !gimple_call_alloca_for_var_p (stmt)
&& !lookup_attribute ("always_inline", DECL_ATTRIBUTES (fn)))
{
inline_forbidden_reason
Index: gimple.c
===================================================================
*** gimple.c (revision 172431)
--- gimple.c (working copy)
*************** gimple_build_call_from_tree (tree t)
*** 303,309 ****
gimple_call_set_tail (call, CALL_EXPR_TAILCALL (t));
gimple_call_set_cannot_inline (call, CALL_CANNOT_INLINE_P (t));
gimple_call_set_return_slot_opt (call, CALL_EXPR_RETURN_SLOT_OPT (t));
! gimple_call_set_from_thunk (call, CALL_FROM_THUNK_P (t));
gimple_call_set_va_arg_pack (call, CALL_EXPR_VA_ARG_PACK (t));
gimple_call_set_nothrow (call, TREE_NOTHROW (t));
gimple_set_no_warning (call, TREE_NO_WARNING (t));
--- 303,314 ----
gimple_call_set_tail (call, CALL_EXPR_TAILCALL (t));
gimple_call_set_cannot_inline (call, CALL_CANNOT_INLINE_P (t));
gimple_call_set_return_slot_opt (call, CALL_EXPR_RETURN_SLOT_OPT (t));
! if (fndecl
! && DECL_BUILT_IN_CLASS (fndecl) == BUILT_IN_NORMAL
! && DECL_FUNCTION_CODE (fndecl) == BUILT_IN_ALLOCA)
! gimple_call_set_alloca_for_var (call, ALLOCA_FOR_VAR_P (t));
! else
! gimple_call_set_from_thunk (call, CALL_FROM_THUNK_P (t));
gimple_call_set_va_arg_pack (call, CALL_EXPR_VA_ARG_PACK (t));
gimple_call_set_nothrow (call, TREE_NOTHROW (t));
gimple_set_no_warning (call, TREE_NO_WARNING (t));
Index: gimple.h
===================================================================
*** gimple.h (revision 172431)
--- gimple.h (working copy)
*************** enum gf_mask {
*** 102,107 ****
--- 102,108 ----
GF_CALL_TAILCALL = 1 << 3,
GF_CALL_VA_ARG_PACK = 1 << 4,
GF_CALL_NOTHROW = 1 << 5,
+ GF_CALL_ALLOCA_FOR_VAR = 1 << 6,
GF_OMP_PARALLEL_COMBINED = 1 << 0,
/* True on an GIMPLE_OMP_RETURN statement if the return does not require
*************** gimple_call_nothrow_p (gimple s)
*** 2329,2334 ****
--- 2330,2358 ----
return (gimple_call_flags (s) & ECF_NOTHROW) != 0;
}
+ /* If FOR_VAR is true, GIMPLE_CALL S is a call to builtin_alloca that
+ is known to be emitted for VLA objects. Those are wrapped by
+ stack_save/stack_restore calls and hence can't lead to unbounded
+ stack growth even when they occur in loops. */
+
+ static inline void
+ gimple_call_set_alloca_for_var (gimple s, bool for_var)
+ {
+ GIMPLE_CHECK (s, GIMPLE_CALL);
+ if (for_var)
+ s->gsbase.subcode |= GF_CALL_ALLOCA_FOR_VAR;
+ else
+ s->gsbase.subcode &= ~GF_CALL_ALLOCA_FOR_VAR;
+ }
+
+ /* Return true of S is a call to builtin_alloca emitted for VLA objects. */
+
+ static inline bool
+ gimple_call_alloca_for_var_p (gimple s)
+ {
+ GIMPLE_CHECK (s, GIMPLE_CALL);
+ return (s->gsbase.subcode & GF_CALL_ALLOCA_FOR_VAR) != 0;
+ }
/* Copy all the GF_CALL_* flags from ORIG_CALL to DEST_CALL. */
