On Tue, Nov 19, 2024 at 11:23:31AM +0100, Jakub Jelinek wrote:
> On Tue, Nov 19, 2024 at 10:25:16AM +0100, Richard Biener wrote:
> > I think it's pretty clear and easy to describe to users what "m " and
> > what "mC" do. But with "pure" this is an odd intermediate state. For both
> > "m " and "mP" you suggest above the new/delete might modify their
> > global state but as you can't rely on the new/delete pair to prevail
> > you cannot rely on the modification to happen. But how do you explain
> > that
>
> If we are willing to make the default not strictly conforming (i.e.
> basically revert PR101480 by default and make the GCC 11.1/11.2 behavior
> the default and allow -fno-sane-operators-new-delete to change to GCC
> 11.3/14.* behavior), I can live with it.
> But we need to make the documentation clear that the default is not strictly
> conforming.
Here is a modified version of the patch to do that.
Or do we want to set the default based on -std= option (-std=gnu* implies
-fassume-sane-operators-new-delete, -std=c++* implies
-fno-assume-sane-operators-new-delete)? Though, not sure what to do for
LTO then.
2024-11-19 Jakub Jelinek <ja...@redhat.com>
PR c++/110137
PR middle-end/101480
gcc/
* doc/invoke.texi (-fassume-sane-operators-new-delete,
-fno-assume-sane-operators-new-delete): Document.
* gimple.cc (gimple_call_fnspec): Handle
-f{,no-}assume-sane-operators-new-delete.
gcc/c-family/
* c.opt (fassume-sane-operators-new-delete): New option.
gcc/testsuite/
* g++.dg/tree-ssa/pr110137-1.C: New test.
* g++.dg/tree-ssa/pr110137-2.C: New test.
* g++.dg/tree-ssa/pr110137-3.C: New test.
* g++.dg/torture/pr10148.C: Add -fno-assume-sane-operators-new-delete
as dg-additional-options.
--- gcc/doc/invoke.texi.jj 2024-11-19 10:23:59.145145887 +0100
+++ gcc/doc/invoke.texi 2024-11-19 12:07:13.942789378 +0100
@@ -213,7 +213,9 @@ in the following sections.
@item C++ Language Options
@xref{C++ Dialect Options,,Options Controlling C++ Dialect}.
@gccoptlist{-fabi-version=@var{n} -fno-access-control
--faligned-new=@var{n} -fargs-in-order=@var{n} -fchar8_t -fcheck-new
+-faligned-new=@var{n} -fargs-in-order=@var{n}
+-fno-assume-sane-operators-new-delete
+-fchar8_t -fcheck-new
-fconcepts -fconstexpr-depth=@var{n} -fconstexpr-cache-depth=@var{n}
-fconstexpr-loop-limit=@var{n} -fconstexpr-ops-limit=@var{n}
-fno-elide-constructors
@@ -3163,6 +3165,35 @@ but few users will need to override the
This flag is enabled by default for @option{-std=c++17}.
+@opindex fno-assume-sane-operators-new-delete
+@opindex fassume-sane-operators-new-delete
+@item -fno-assume-sane-operators-new
+The C++ standard allows replacing the global @code{new}, @code{new[]},
+@code{delete} and @code{delete[]} operators, though a lot of C++ programs
+don't replace them and just use the implementation provided version.
+Furthermore, the C++ standard allows omitting those calls if they are
+made from new or delete expressions (and by extension the same is
+assumed if @code{__builtin_operator_new} or @code{__builtin_operator_delete}
+functions are used).
+This option allows control over some optimizations around calls
+to those operators.
+With @code{-fassume-sane-operators-new-delete} option GCC may assume that
+calls to the replaceable global operators from new or delete expressions or
+from @code{__builtin_operator_new} or @code{__builtin_operator_delete} calls
+don't read or modify any global variables or variables whose address could
+escape to the operators (global state; except for @code{errno} for the
+@code{new} and @code{new[]} operators).
+This allows most optimizations across those calls and is something that
+the implementation provided operators satisfy unless @code{malloc}
+implementation details are observable in the code or unless @code{malloc}
+hooks are used, but might not be satisfied if a program replaces those
+operators. This behavior is enabled by default.
+With @code{-fno-assume-sane-operators-new-delete} option GCC must
+assume all these calls (whether from new or delete expressions or called
+directly) may read and write global state unless proven otherwise (e.g.@:
+when GCC compiles their implementation). Use this option if those
+operators are or may be replaced and code needs to expect such behavior.
+
@opindex fchar8_t
@opindex fno-char8_t
@item -fchar8_t
--- gcc/gimple.cc.jj 2024-11-16 10:22:38.386770817 +0100
+++ gcc/gimple.cc 2024-11-19 11:45:33.386136116 +0100
@@ -1600,12 +1600,22 @@ gimple_call_fnspec (const gcall *stmt)
&& DECL_IS_OPERATOR_DELETE_P (fndecl)
&& DECL_IS_REPLACEABLE_OPERATOR (fndecl)
&& gimple_call_from_new_or_delete (stmt))
- return ". o ";
+ {
+ if (flag_assume_sane_operators_new_delete)
+ return ".co ";
+ else
+ return ". o ";
+ }
/* Similarly operator new can be treated as malloc. */
if (fndecl
&& DECL_IS_REPLACEABLE_OPERATOR_NEW_P (fndecl)
&& gimple_call_from_new_or_delete (stmt))
- return "m ";
+ {
+ if (flag_assume_sane_operators_new_delete)
+ return "mC";
+ else
+ return "m ";
+ }
return "";
}
--- gcc/c-family/c.opt.jj 2024-11-18 09:05:00.182283546 +0100
+++ gcc/c-family/c.opt 2024-11-19 11:31:29.381038177 +0100
@@ -1690,6 +1690,10 @@ fasm
C ObjC C++ ObjC++ Var(flag_no_asm, 0)
Recognize the \"asm\" keyword.
+fassume-sane-operators-new-delete
+C++ ObjC++ LTO Var(flag_assume_sane_operators_new_delete) Init(1)
+Assume C++ replaceable global operators new, new[], delete, delete[] don't
read or write visible global state.
+
; Define extra predefined macros for use in libgcc.
fbuilding-libgcc
C ObjC C++ ObjC++ Undocumented Var(flag_building_libgcc)
--- gcc/testsuite/g++.dg/tree-ssa/pr110137-1.C.jj 2024-11-19
11:30:24.866947846 +0100
+++ gcc/testsuite/g++.dg/tree-ssa/pr110137-1.C 2024-11-19 11:52:27.996287689
+0100
@@ -0,0 +1,74 @@
+// PR c++/110137
+// { dg-do compile }
+// { dg-options "-O2 -fdump-tree-optimized" }
+// { dg-final { scan-tree-dump "j = 2;" "optimized" } } */
+// { dg-final { scan-tree-dump "m = 2;" "optimized" } } */
+// { dg-final { scan-tree-dump-not "q = 2;" "optimized" } } */
+// { dg-final { scan-tree-dump-not "t = 2;" "optimized" } } */
+// { dg-final { scan-tree-dump-not "k = 1;" "optimized" } } */
+// { dg-final { scan-tree-dump-times "r = 1;" 2 "optimized" } } */
+
+int i, j, k, l, m, n, o, q, r, s, t, u;
+
+void *
+foo ()
+{
+ i = 1;
+ j = 2;
+ void *p = ::operator new (32);
+ j = 3;
+ k = i;
+ return p;
+}
+
+void
+bar (void *p)
+{
+ l = 1;
+ m = 2;
+ ::operator delete (p);
+ m = 3;
+ n = l;
+}
+
+int *
+baz ()
+{
+ o = 1;
+ q = 2;
+ int *p = new int;
+ q = 3;
+ r = o;
+ return p;
+}
+
+void
+qux (int *p)
+{
+ s = 1;
+ t = 2;
+ delete p;
+ t = 3;
+ u = s;
+}
+
+void *
+corge ()
+{
+ o = 1;
+ q = 2;
+ void *p = __builtin_operator_new (32);
+ q = 3;
+ r = o;
+ return p;
+}
+
+void
+waldo (void *p)
+{
+ s = 1;
+ t = 2;
+ __builtin_operator_delete (p);
+ t = 3;
+ u = s;
+}
--- gcc/testsuite/g++.dg/tree-ssa/pr110137-2.C.jj 2024-11-19
11:30:24.866947846 +0100
+++ gcc/testsuite/g++.dg/tree-ssa/pr110137-2.C 2024-11-19 11:52:18.473422017
+0100
@@ -0,0 +1,74 @@
+// PR c++/110137
+// { dg-do compile }
+// { dg-options "-O2 -fdump-tree-optimized -fassume-sane-operators-new-delete"
}
+// { dg-final { scan-tree-dump "j = 2;" "optimized" } } */
+// { dg-final { scan-tree-dump "m = 2;" "optimized" } } */
+// { dg-final { scan-tree-dump-not "q = 2;" "optimized" } } */
+// { dg-final { scan-tree-dump-not "t = 2;" "optimized" } } */
+// { dg-final { scan-tree-dump-not "k = 1;" "optimized" } } */
+// { dg-final { scan-tree-dump-times "r = 1;" 2 "optimized" } } */
+
+int i, j, k, l, m, n, o, q, r, s, t, u;
+
+void *
+foo ()
+{
+ i = 1;
+ j = 2;
+ void *p = ::operator new (32);
+ j = 3;
+ k = i;
+ return p;
+}
+
+void
+bar (void *p)
+{
+ l = 1;
+ m = 2;
+ ::operator delete (p);
+ m = 3;
+ n = l;
+}
+
+int *
+baz ()
+{
+ o = 1;
+ q = 2;
+ int *p = new int;
+ q = 3;
+ r = o;
+ return p;
+}
+
+void
+qux (int *p)
+{
+ s = 1;
+ t = 2;
+ delete p;
+ t = 3;
+ u = s;
+}
+
+void *
+corge ()
+{
+ o = 1;
+ q = 2;
+ void *p = __builtin_operator_new (32);
+ q = 3;
+ r = o;
+ return p;
+}
+
+void
+waldo (void *p)
+{
+ s = 1;
+ t = 2;
+ __builtin_operator_delete (p);
+ t = 3;
+ u = s;
+}
--- gcc/testsuite/g++.dg/tree-ssa/pr110137-3.C.jj 2024-11-19
11:30:24.866947846 +0100
+++ gcc/testsuite/g++.dg/tree-ssa/pr110137-3.C 2024-11-19 11:30:24.866947846
+0100
@@ -0,0 +1,76 @@
+// PR c++/110137
+// { dg-do compile }
+// { dg-options "-O2 -fdump-tree-optimized
-fno-assume-sane-operators-new-delete" }
+// { dg-final { scan-tree-dump "j = 2;" "optimized" } } */
+// { dg-final { scan-tree-dump "m = 2;" "optimized" } } */
+// { dg-final { scan-tree-dump-times "q = 2;" 2 "optimized" } } */
+// { dg-final { scan-tree-dump-times "t = 2;" 2 "optimized" } } */
+// { dg-final { scan-tree-dump-not "k = 1;" "optimized" } } */
+// { dg-final { scan-tree-dump-not "n = 1;" "optimized" } } */
+// { dg-final { scan-tree-dump-not "r = 1;" "optimized" } } */
+// { dg-final { scan-tree-dump-not "u = 1;" "optimized" } } */
+
+int i, j, k, l, m, n, o, q, r, s, t, u;
+
+void *
+foo ()
+{
+ i = 1;
+ j = 2;
+ void *p = ::operator new (32);
+ j = 3;
+ k = i;
+ return p;
+}
+
+void
+bar (void *p)
+{
+ l = 1;
+ m = 2;
+ ::operator delete (p);
+ m = 3;
+ n = l;
+}
+
+int *
+baz ()
+{
+ o = 1;
+ q = 2;
+ int *p = new int;
+ q = 3;
+ r = o;
+ return p;
+}
+
+void
+qux (int *p)
+{
+ s = 1;
+ t = 2;
+ delete p;
+ t = 3;
+ u = s;
+}
+
+void *
+corge ()
+{
+ o = 1;
+ q = 2;
+ void *p = __builtin_operator_new (32);
+ q = 3;
+ r = o;
+ return p;
+}
+
+void
+waldo (void *p)
+{
+ s = 1;
+ t = 2;
+ __builtin_operator_delete (p);
+ t = 3;
+ u = s;
+}
--- gcc/testsuite/g++.dg/torture/pr10148.C.jj 2024-09-13 16:09:39.744357235
+0200
+++ gcc/testsuite/g++.dg/torture/pr10148.C 2024-11-19 11:59:39.308203533
+0100
@@ -1,5 +1,6 @@
/* { dg-do run } */
/* { dg-skip-if "requires hosted libstdc++ for stdlib malloc" { ! hostedlib }
} */
+/* { dg-additional-options "-fno-assume-sane-operators-new-delete" } */
#include <stdlib.h>
#include <assert.h>
Jakub
