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. 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. Signed-off-by: Andrew Pinski <quic_apin...@quicinc.com> --- 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/tree-ssa-dce.cc | 44 ++++++++++++++++++++ 6 files changed, 163 insertions(+) create mode 100644 gcc/testsuite/g++.dg/tree-ssa/cxa_atexit-1.C create mode 100644 gcc/testsuite/g++.dg/tree-ssa/cxa_atexit-2.C create mode 100644 gcc/testsuite/g++.dg/tree-ssa/cxa_atexit-3.C create mode 100644 gcc/testsuite/g++.dg/tree-ssa/cxa_atexit-4.C create mode 100644 gcc/testsuite/g++.dg/tree-ssa/cxa_atexit-5.C 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 00000000000..1f5f431c7e4 --- /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" 1 "cddce1" } } */ +/* { dg-final { scan-tree-dump-not "__cxa_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 00000000000..4d0656b455c --- /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" "cddce1" } } */ +/* { dg-final { scan-tree-dump-times "__cxa_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 00000000000..03a19209661 --- /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" "cddce1" } } */ +/* { dg-final { scan-tree-dump-times "__cxa_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 00000000000..b85a7efd16b --- /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" 1 "cddce1" } } */ +/* { dg-final { scan-tree-dump-not "__cxa_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 00000000000..f96395df913 --- /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" 1 "dce2" } } */ +/* { dg-final { scan-tree-dump-not "__cxa_atexit" "optimized" } } */ + diff --git a/gcc/tree-ssa-dce.cc b/gcc/tree-ssa-dce.cc index 636c471d4c8..762218a04fe 100644 --- a/gcc/tree-ssa-dce.cc +++ b/gcc/tree-ssa-dce.cc @@ -124,6 +124,41 @@ keep_all_vdefs_p () return optimize_debug; } +/* True if CALLEE is the function __cxa_atexit. */ + +static inline bool +is_cxa_atexit (const_tree callee) +{ + if (callee != NULL_TREE + && strcmp (IDENTIFIER_POINTER (DECL_NAME (callee)), "__cxa_atexit") == 0) + return true; + return false; +} + +/* True if STMT is a call to __cxa_atexit and the first argument to that + call is a pure/const non looping function decl. */ + +static inline bool +is_removable_cxa_atexit_call (gimple *stmt) +{ + tree callee = gimple_call_fndecl (stmt); + if (!is_cxa_atexit (callee)) + return false; + if (gimple_call_num_args (stmt) != 3) + return false; + tree arg = gimple_call_arg (stmt, 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 (flags & ECF_NORETURN) + return false; + 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 +286,10 @@ 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 +665,8 @@ 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 +971,9 @@ 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); -- 2.43.0