https://gcc.gnu.org/g:c9dd853680b12d9c9def5de61abde5d057c526ba
commit r15-308-gc9dd853680b12d9c9def5de61abde5d057c526ba
Author: Andrew Pinski <quic_apin...@quicinc.com>
Date: Fri Mar 15 16:34:22 2024 -0700
DCE __cxa_atexit calls where the function is pure/const [PR19661]
In C++ sometimes you have a deconstructor function which is "empty", like
for an
example with unions or with arrays. The front-end might not know it is
empty either
so this should be done on during optimization.o
To implement it I added it to DCE where we mark if a statement is necessary
or not.
Bootstrapped and tested on x86_64-linux-gnu with no regressions.
Changes since v1:
* v2: Add support for __aeabi_atexit for arm-*eabi. Add extra comments.
Add cxa_atexit-5.C testcase for -fPIC case.
* v3: Fix testcases for the __aeabi_atexit (forgot to do in the v2).
PR tree-optimization/19661
gcc/ChangeLog:
* tree-ssa-dce.cc (is_cxa_atexit): New function.
(is_removable_cxa_atexit_call): New function.
(mark_stmt_if_obviously_necessary): Don't mark removable
cxa_at_exit calls.
(mark_all_reaching_defs_necessary_1): Likewise.
(propagate_necessity): Likewise.
gcc/testsuite/ChangeLog:
* g++.dg/tree-ssa/cxa_atexit-1.C: New test.
* g++.dg/tree-ssa/cxa_atexit-2.C: New test.
* g++.dg/tree-ssa/cxa_atexit-3.C: New test.
* g++.dg/tree-ssa/cxa_atexit-4.C: New test.
* g++.dg/tree-ssa/cxa_atexit-5.C: New test.
* g++.dg/tree-ssa/cxa_atexit-6.C: New test.
Signed-off-by: Andrew Pinski <quic_apin...@quicinc.com>
Diff:
---
gcc/testsuite/g++.dg/tree-ssa/cxa_atexit-1.C | 20 ++++++++++
gcc/testsuite/g++.dg/tree-ssa/cxa_atexit-2.C | 21 ++++++++++
gcc/testsuite/g++.dg/tree-ssa/cxa_atexit-3.C | 19 +++++++++
gcc/testsuite/g++.dg/tree-ssa/cxa_atexit-4.C | 20 ++++++++++
gcc/testsuite/g++.dg/tree-ssa/cxa_atexit-5.C | 39 +++++++++++++++++++
gcc/testsuite/g++.dg/tree-ssa/cxa_atexit-6.C | 24 ++++++++++++
gcc/tree-ssa-dce.cc | 58 ++++++++++++++++++++++++++++
7 files changed, 201 insertions(+)
diff --git a/gcc/testsuite/g++.dg/tree-ssa/cxa_atexit-1.C
b/gcc/testsuite/g++.dg/tree-ssa/cxa_atexit-1.C
new file mode 100644
index 000000000000..82ff3d2b7783
--- /dev/null
+++ b/gcc/testsuite/g++.dg/tree-ssa/cxa_atexit-1.C
@@ -0,0 +1,20 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-cddce1-details -fdump-tree-optimized" } */
+// { dg-require-effective-target cxa_atexit }
+/* PR tree-optimization/19661 */
+
+/* The call to axexit should be removed as A::~A() is a pure/const function
call
+ and there is no visible effect if A::~A() call does not happen. */
+
+struct A {
+ A();
+ ~A() {}
+};
+
+void foo () {
+ static A a;
+}
+
+/* { dg-final { scan-tree-dump-times "Deleting :
(?:__cxxabiv1::__cxa_atexit|__aeabiv1::__aeabi_atexit)" 1 "cddce1" } } */
+/* { dg-final { scan-tree-dump-not "__cxa_atexit|__aeabi_atexit" "optimized" }
} */
+
diff --git a/gcc/testsuite/g++.dg/tree-ssa/cxa_atexit-2.C
b/gcc/testsuite/g++.dg/tree-ssa/cxa_atexit-2.C
new file mode 100644
index 000000000000..726b6d7f1561
--- /dev/null
+++ b/gcc/testsuite/g++.dg/tree-ssa/cxa_atexit-2.C
@@ -0,0 +1,21 @@
+/* { dg-do compile { target c++11 } } */
+/* { dg-options "-O2 -fdump-tree-cddce1-details -fdump-tree-optimized" } */
+// { dg-require-effective-target cxa_atexit }
+/* PR tree-optimization/19661 */
+
+/* The call to axexit should be not removed as A::~A() as it marked with
noipa. */
+
+struct A {
+ A();
+ ~A();
+};
+
+[[gnu::noipa]] A::~A() {}
+
+void foo () {
+ static A a;
+}
+
+/* { dg-final { scan-tree-dump-not "Deleting :
(?:__cxxabiv1::__cxa_atexit|__aeabiv1::__aeabi_atexit)" "cddce1" } } */
+/* { dg-final { scan-tree-dump-times "(?:__cxa_atexit|__aeabi_atexit)" 1
"optimized" } } */
+
diff --git a/gcc/testsuite/g++.dg/tree-ssa/cxa_atexit-3.C
b/gcc/testsuite/g++.dg/tree-ssa/cxa_atexit-3.C
new file mode 100644
index 000000000000..42cc7ccb11ba
--- /dev/null
+++ b/gcc/testsuite/g++.dg/tree-ssa/cxa_atexit-3.C
@@ -0,0 +1,19 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-cddce1-details -fdump-tree-optimized" } */
+// { dg-require-effective-target cxa_atexit }
+/* PR tree-optimization/19661 */
+
+/* We should not remove the call to atexit as A::~A is unknown. */
+
+struct A {
+ A();
+ ~A();
+};
+
+void foo () {
+ static A a;
+}
+
+/* { dg-final { scan-tree-dump-not "Deleting :
(?:__cxxabiv1::__cxa_atexit|__aeabiv1::__aeabi_atexit)" "cddce1" } } */
+/* { dg-final { scan-tree-dump-times "(?:__cxa_atexit|__aeabi_atexit)" 1
"optimized" } } */
+
diff --git a/gcc/testsuite/g++.dg/tree-ssa/cxa_atexit-4.C
b/gcc/testsuite/g++.dg/tree-ssa/cxa_atexit-4.C
new file mode 100644
index 000000000000..591c1c0552a1
--- /dev/null
+++ b/gcc/testsuite/g++.dg/tree-ssa/cxa_atexit-4.C
@@ -0,0 +1,20 @@
+/* { dg-do compile { target c++11 } } */
+/* { dg-options "-O2 -fdump-tree-cddce1-details -fdump-tree-optimized -w" } */
+// { dg-require-effective-target cxa_atexit }
+/* PR tree-optimization/19661 */
+
+/* The call to axexit should be removed as A::~A() is a pure/const function
call
+ and there is no visible effect if A::~A() call does not happen. */
+
+struct A {
+ A();
+ [[gnu::pure]] ~A();
+};
+
+void foo () {
+ static A a;
+}
+
+/* { dg-final { scan-tree-dump-times "Deleting :
(?:__cxxabiv1::__cxa_atexit|__aeabiv1::__aeabi_atexit)" 1 "cddce1" } } */
+/* { dg-final { scan-tree-dump-not "(?:__cxa_atexit|__aeabi_atexit)"
"optimized" } } */
+
diff --git a/gcc/testsuite/g++.dg/tree-ssa/cxa_atexit-5.C
b/gcc/testsuite/g++.dg/tree-ssa/cxa_atexit-5.C
new file mode 100644
index 000000000000..e59f70c1ed4a
--- /dev/null
+++ b/gcc/testsuite/g++.dg/tree-ssa/cxa_atexit-5.C
@@ -0,0 +1,39 @@
+/* { dg-do compile { target c++20 } } */
+/* { dg-options "-O2 -fdump-tree-dce2-details -fdump-tree-optimized" } */
+// { dg-require-effective-target cxa_atexit }
+/* PR tree-optimization/19661 */
+
+/* The call to axexit should be removed as constant_init::~constant_init is a
pure/const function call
+ and there is no visible effect if constant_init::~constant_init() call does
not happen. */
+/* This takes until DCE2 as constant_init::~constant_init is not figured out
being pure/const until late. */
+
+extern "C" int puts(const char*);
+
+struct A
+{
+ constexpr A() { }
+ ~A() { puts("bye"); }
+};
+
+namespace
+{
+ struct constant_init
+ {
+ union {
+ A obj;
+ };
+ constexpr constant_init() : obj() { }
+
+ ~constant_init() { /* do nothing, union member is not destroyed */ }
+ };
+
+
+ // Single-threaded fallback buffer.
+ constinit constant_init global;
+}
+
+extern "C" A* get() { return &global.obj; }
+
+/* { dg-final { scan-tree-dump-times "Deleting :
(?:__cxxabiv1::__cxa_atexit|__aeabiv1::__aeabi_atexit)" 1 "dce2" } } */
+/* { dg-final { scan-tree-dump-not "(?:__cxa_atexit|__aeabi_atexit)"
"optimized" } } */
+
diff --git a/gcc/testsuite/g++.dg/tree-ssa/cxa_atexit-6.C
b/gcc/testsuite/g++.dg/tree-ssa/cxa_atexit-6.C
new file mode 100644
index 000000000000..f6599a3c9f45
--- /dev/null
+++ b/gcc/testsuite/g++.dg/tree-ssa/cxa_atexit-6.C
@@ -0,0 +1,24 @@
+/* { dg-do compile } */
+/* { dg-require-effective-target fpic } */
+/* { dg-options "-O2 -fdump-tree-cddce1-details -fdump-tree-optimized -fPIC" }
*/
+// { dg-require-effective-target cxa_atexit }
+/* PR tree-optimization/19661 */
+
+/* The call to axexit should not be removed as A::~A() cannot be figured if it
+ is a pure/const function call as the function call g does not bind locally.
*/
+
+__attribute__((noinline))
+void g() {}
+
+struct A {
+ A();
+ ~A() { g(); }
+};
+
+void foo () {
+ static A a;
+}
+
+/* { dg-final { scan-tree-dump-not "Deleting :
(?:__cxxabiv1::__cxa_atexit|__aeabiv1::__aeabi_atexit)" "cddce1" } } */
+/* { dg-final { scan-tree-dump-times "(?:__cxa_atexit|__aeabi_atexit)" 1
"optimized" } } */
+
diff --git a/gcc/tree-ssa-dce.cc b/gcc/tree-ssa-dce.cc
index 636c471d4c89..69249c73013f 100644
--- a/gcc/tree-ssa-dce.cc
+++ b/gcc/tree-ssa-dce.cc
@@ -124,6 +124,55 @@ keep_all_vdefs_p ()
return optimize_debug;
}
+/* 1 if CALLEE is the function __cxa_atexit.
+ 2 if CALLEE is the function __aeabi_atexit.
+ 0 otherwise. */
+
+static inline int
+is_cxa_atexit (const_tree callee)
+{
+ if (callee != NULL_TREE
+ && strcmp (IDENTIFIER_POINTER (DECL_NAME (callee)), "__cxa_atexit") == 0)
+ return 1;
+ if (callee != NULL_TREE
+ && strcmp (IDENTIFIER_POINTER (DECL_NAME (callee)), "__aeabi_atexit") ==
0)
+ return 2;
+ return 0;
+}
+
+/* True if STMT is a call to __cxa_atexit (or __aeabi_atexit)
+ and the function argument to that call is a const or pure
+ non-looping function decl. */
+
+static inline bool
+is_removable_cxa_atexit_call (gimple *stmt)
+{
+ tree callee = gimple_call_fndecl (stmt);
+ int functype = is_cxa_atexit (callee);
+ if (!functype)
+ return false;
+ if (gimple_call_num_args (stmt) != 3)
+ return false;
+
+ /* The function argument is the 1st argument for __cxa_atexit
+ or the 2nd argument for __eabi_atexit. */
+ tree arg = gimple_call_arg (stmt, functype == 2 ? 1 : 0);
+ if (TREE_CODE (arg) != ADDR_EXPR)
+ return false;
+ arg = TREE_OPERAND (arg, 0);
+ if (TREE_CODE (arg) != FUNCTION_DECL)
+ return false;
+ int flags = flags_from_decl_or_type (arg);
+
+ /* If the function is noreturn then it cannot be removed. */
+ if (flags & ECF_NORETURN)
+ return false;
+
+ /* The function needs to be const or pure and non looping. */
+ return (flags & (ECF_CONST|ECF_PURE))
+ && !(flags & ECF_LOOPING_CONST_OR_PURE);
+}
+
/* If STMT is not already marked necessary, mark it, and add it to the
worklist if ADD_TO_WORKLIST is true. */
@@ -251,6 +300,10 @@ mark_stmt_if_obviously_necessary (gimple *stmt, bool
aggressive)
&& DECL_IS_REPLACEABLE_OPERATOR_NEW_P (callee))
return;
+ /* For __cxa_atexit calls, don't mark as necessary right away. */
+ if (is_removable_cxa_atexit_call (stmt))
+ return;
+
/* IFN_GOACC_LOOP calls are necessary in that they are used to
represent parameter (i.e. step, bound) of a lowered OpenACC
partitioned loop. But this kind of partitioned loop might not
@@ -626,6 +679,8 @@ mark_all_reaching_defs_necessary_1 (ao_ref *ref
ATTRIBUTE_UNUSED,
|| DECL_IS_OPERATOR_DELETE_P (callee))
&& gimple_call_from_new_or_delete (call))
return false;
+ if (is_removable_cxa_atexit_call (call))
+ return false;
}
if (! gimple_clobber_p (def_stmt))
@@ -930,6 +985,9 @@ propagate_necessity (bool aggressive)
&& gimple_call_from_new_or_delete (call))
continue;
+ if (is_removable_cxa_atexit_call (call))
+ continue;
+
/* Calls implicitly load from memory, their arguments
in addition may explicitly perform memory loads. */
mark_all_reaching_defs_necessary (call);
