[Bug c++/90569] __STDCPP_DEFAULT_NEW_ALIGNMENT__ is wrong for i386-pc-solaris2.11

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90569

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2019-05-22
     Ever confirmed|0                           |1

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
I thought we could workaround this in libstdc++ like so:

diff --git a/libstdc++-v3/libsupc++/Makefile.am
b/libstdc++-v3/libsupc++/Makefile.am
index eec7b953514..a50a9848461 100644
--- a/libstdc++-v3/libsupc++/Makefile.am
+++ b/libstdc++-v3/libsupc++/Makefile.am
@@ -129,6 +129,8 @@ cp-demangle.o: cp-demangle.c


 # Use special rules for the C++17 sources so that the proper flags are passed.
+new_op.lo: new_op.cc
+       $(LTCXXCOMPILE) -std=gnu++1z -c $<
 new_opa.lo: new_opa.cc
        $(LTCXXCOMPILE) -std=gnu++1z -c $<
 new_opant.lo: new_opant.cc
diff --git a/libstdc++-v3/libsupc++/Makefile.in
b/libstdc++-v3/libsupc++/Makefile.in
index 5d8ac5ca0ba..0e3cbff0055 100644
--- a/libstdc++-v3/libsupc++/Makefile.in
+++ b/libstdc++-v3/libsupc++/Makefile.in
@@ -956,6 +956,8 @@ cp-demangle.o: cp-demangle.c
        $(C_COMPILE) -DIN_GLIBCPP_V3 -Wno-error -c $<

 # Use special rules for the C++17 sources so that the proper flags are passed.
+new_op.lo: new_op.cc
+       $(LTCXXCOMPILE) -std=gnu++1z -c $<
 new_opa.lo: new_opa.cc
        $(LTCXXCOMPILE) -std=gnu++1z -c $<
 new_opant.lo: new_opant.cc
diff --git a/libstdc++-v3/libsupc++/new_op.cc
b/libstdc++-v3/libsupc++/new_op.cc
index 863530b7564..203c57d9171 100644
--- a/libstdc++-v3/libsupc++/new_op.cc
+++ b/libstdc++-v3/libsupc++/new_op.cc
@@ -27,6 +27,9 @@
 #include <cstdlib>
 #include <bits/exception_defines.h>
 #include "new"
+#if defined __sun__ || defined __i386__
+# include <cstddef>
+#endif

 using std::new_handler;
 using std::bad_alloc;
@@ -41,6 +44,14 @@ extern "C" void *malloc (std::size_t);
 _GLIBCXX_WEAK_DEFINITION void *
 operator new (std::size_t sz) _GLIBCXX_THROW (std::bad_alloc)
 {
+#if defined __sun__ || defined __i386__
+  if (sz >= alignof(std::max_align_t))
+    {
+      std::align_val_t al{alignof(std::max_align_t)};
+      return ::operator new(sz, al);
+    }
+#endif
+
   void *p;

   /* malloc (0) is unpredictable; avoid it.  */



This would force operator new to use aligned_alloc instead of malloc for
allocations that might be for objects large enough to require greater alignment
than malloc guarantees. But since Solaris 11 doesn't appear to define
aligned_alloc, this would use the fallback implementation in
libsupc++/new_opa.cc which is much less efficient than plain malloc.