The following allows a base term to be derived from an existing
MEM_EXPR, notably the points-to set of a MEM_REF base. For the
testcase in the PR this helps RTL DSE elide stores to a stack
temporary. This covers pointers to NONLOCAL which can be mapped
to arg_base_value, helping to disambiguate against other special
bases (ADDRESS) as well as PARM_DECL accesses.
Bootstrapped and tested on x86_64-unknown-linux-gnu.
This is an attempt to recover some of the losses from dumbing down
find_base_{term,value}. I did give my ideas how to properly do
this during stage1 a start, I will post a short incomplete RFC series
later today.
OK for trunk?
I've included all languages in testing and also tested with -m32 but
details of RTL alias analysis might escape me ...
Thanks,
Richard.
PR rtl-optimization/113597
* alias.cc (find_base_term): Add argument for the whole mem
and derive a base term from its MEM_EXPR.
(true_dependence_1): Pass down the MEMs to find_base_term.
(write_dependence_p): Likewise.
(may_alias_p): Likewise.
---
gcc/alias.cc | 43 ++++++++++++++++++++++++++++++++++++-------
1 file changed, 36 insertions(+), 7 deletions(-)
diff --git a/gcc/alias.cc b/gcc/alias.cc
index 6fad4b29d31..e33c56b0e80 100644
--- a/gcc/alias.cc
+++ b/gcc/alias.cc
@@ -40,6 +40,9 @@ along with GCC; see the file COPYING3. If not see
#include "rtl-iter.h"
#include "cgraph.h"
#include "ipa-utils.h"
+#include "stringpool.h"
+#include "value-range.h"
+#include "tree-ssanames.h"
/* The aliasing API provided here solves related but different problems:
@@ -190,6 +193,10 @@ static struct {
arguments, since we do not know at this level whether accesses
based on different arguments can alias. The ADDRESS has id 0.
+ This is solely useful to disambiguate against other ADDRESS
+ bases as we know incoming pointers cannot point to local
+ stack, frame or argument space.
+
2. stack_pointer_rtx, frame_pointer_rtx, hard_frame_pointer_rtx
(if distinct from frame_pointer_rtx) and arg_pointer_rtx.
Each of these rtxes has a separate ADDRESS associated with it,
@@ -2113,12 +2120,34 @@ find_base_term (rtx x, vec<std::pair<cselib_val *,
to avoid visiting them multiple times. We unwind that changes here. */
static rtx
-find_base_term (rtx x)
+find_base_term (rtx x, const_rtx mem = NULL_RTX)
{
auto_vec<std::pair<cselib_val *, struct elt_loc_list *>, 32> visited_vals;
rtx res = find_base_term (x, visited_vals);
for (unsigned i = 0; i < visited_vals.length (); ++i)
visited_vals[i].first->locs = visited_vals[i].second;
+ if (!res && mem && MEM_EXPR (mem))
+ {
+ tree base = get_base_address (MEM_EXPR (mem));
+ if (TREE_CODE (base) == PARM_DECL
+ && DECL_RTL_SET_P (base))
+ /* We need to look at how we expanded a PARM_DECL. It might be in
+ the argument space (UNIQUE_BASE_VALUE_ARGP) or it might
+ be spilled (UNIQUE_BASE_VALUE_FP/UNIQUE_BASE_VALUE_HFP). */
+ res = find_base_term (DECL_RTL (base));
+ else if (TREE_CODE (base) == MEM_REF
+ && TREE_CODE (TREE_OPERAND (base, 0)) == SSA_NAME
+ && SSA_NAME_PTR_INFO (TREE_OPERAND (base, 0)))
+ {
+ auto pt = &SSA_NAME_PTR_INFO (TREE_OPERAND (base, 0))->pt;
+ if (pt->nonlocal
+ && !pt->anything
+ && !pt->escaped
+ && !pt->ipa_escaped
+ && bitmap_empty_p (pt->vars))
+ res = arg_base_value;
+ }
+ }
return res;
}
@@ -3035,13 +3064,13 @@ true_dependence_1 (const_rtx mem, machine_mode
mem_mode, rtx mem_addr,
if (MEM_ADDR_SPACE (mem) != MEM_ADDR_SPACE (x))
return true;
- base = find_base_term (x_addr);
+ base = find_base_term (x_addr, x);
if (base && (GET_CODE (base) == LABEL_REF
|| (GET_CODE (base) == SYMBOL_REF
&& CONSTANT_POOL_ADDRESS_P (base))))
return false;
- rtx mem_base = find_base_term (true_mem_addr);
+ rtx mem_base = find_base_term (true_mem_addr, mem);
if (! base_alias_check (x_addr, base, true_mem_addr, mem_base,
GET_MODE (x), mem_mode))
return false;
@@ -3142,7 +3171,7 @@ write_dependence_p (const_rtx mem,
if (MEM_ADDR_SPACE (mem) != MEM_ADDR_SPACE (x))
return true;
- base = find_base_term (true_mem_addr);
+ base = find_base_term (true_mem_addr, mem);
if (! writep
&& base
&& (GET_CODE (base) == LABEL_REF
@@ -3150,7 +3179,7 @@ write_dependence_p (const_rtx mem,
&& CONSTANT_POOL_ADDRESS_P (base))))
return false;
- rtx x_base = find_base_term (true_x_addr);
+ rtx x_base = find_base_term (true_x_addr, x);
if (! base_alias_check (true_x_addr, x_base, true_mem_addr, base,
GET_MODE (x), GET_MODE (mem)))
return false;
@@ -3265,8 +3294,8 @@ may_alias_p (const_rtx mem, const_rtx x)
if (MEM_ADDR_SPACE (mem) != MEM_ADDR_SPACE (x))
return true;
- rtx x_base = find_base_term (x_addr);
- rtx mem_base = find_base_term (mem_addr);
+ rtx x_base = find_base_term (x_addr, x);
+ rtx mem_base = find_base_term (mem_addr, mem);
if (! base_alias_check (x_addr, x_base, mem_addr, mem_base,
GET_MODE (x), GET_MODE (mem_addr)))
return false;
--
2.35.3
