12 files changed, 146 insertions, 7 deletions
diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index b0c8803..cbbeee4 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,20 @@
+2009-05-28  Dave Korn  <dave.korn.cygwin@gmail.com>
+
+	PR target/37216
+
+	* configure.ac (HAVE_GAS_ALIGNED_COMM):  Add autoconf test and
+	macro definition for support of three-operand format aligned
+	.comm directive in assembler on cygwin/pe/mingw target OS.
+	* configure:  Regenerate.
+	* config.h:  Regenerate.
+
+	* config/i386/winnt.c (i386_pe_asm_output_aligned_decl_common):  Use
+	aligned form of .comm directive if -mpe-aligned-commons is in effect.
+	* config/i386/cygming.opt (-mpe-aligned-commons):  Add new option.
+
+	* doc/invoke.texi (-mpe-aligned-commons):  Document new target option.
+	* doc/tm.texi (ASM_OUTPUT_COMMON):  Document zero size commons.
+
 2009-05-28  Ira Rosen  <irar@il.ibm.com>
 
 	PR tree-optimization/40254
diff --git a/gcc/config.in b/gcc/config.in
index 76a7810..9f53173 100644
--- a/gcc/config.in
+++ b/gcc/config.in
@@ -844,6 +844,13 @@
 #endif
 
 
+/* Define if your assembler supports specifying the alignment of objects
+   allocated using the GAS .comm command. */
+#ifndef USED_FOR_TARGET
+#undef HAVE_GAS_ALIGNED_COMM
+#endif
+
+
 /* Define if your assembler supports .balign and .p2align. */
 #ifndef USED_FOR_TARGET
 #undef HAVE_GAS_BALIGN_AND_P2ALIGN
diff --git a/gcc/config/i386/cygming.opt b/gcc/config/i386/cygming.opt
index 7c29eb8..e845a0d 100644
--- a/gcc/config/i386/cygming.opt
+++ b/gcc/config/i386/cygming.opt
@@ -45,3 +45,7 @@ Set Windows defines
 mwindows
 Target
 Create GUI application
+
+mpe-aligned-commons
+Target Var(use_pe_aligned_common) Init(HAVE_GAS_ALIGNED_COMM)
+Use the GNU extension to the PE format for aligned common data
diff --git a/gcc/config/i386/winnt.c b/gcc/config/i386/winnt.c
index 3d88517..812cf79 100644
--- a/gcc/config/i386/winnt.c
+++ b/gcc/config/i386/winnt.c
@@ -499,8 +499,11 @@ i386_pe_asm_output_aligned_decl_common (FILE *stream, tree decl,
 {
   HOST_WIDE_INT rounded;
 
-  /* Compute as in assemble_noswitch_variable, since we don't actually
-     support aligned common.  */
+  /* Compute as in assemble_noswitch_variable, since we don't have
+     support for aligned common on older binutils.  We must also
+     avoid emitting a common symbol of size zero, as this is the
+     overloaded representation that indicates an undefined external
+     symbol in the PE object file format.  */
   rounded = size ? size : 1;
   rounded += (BIGGEST_ALIGNMENT / BITS_PER_UNIT) - 1;
   rounded = (rounded / (BIGGEST_ALIGNMENT / BITS_PER_UNIT)
@@ -510,9 +513,13 @@ i386_pe_asm_output_aligned_decl_common (FILE *stream, tree decl,
 
   fprintf (stream, "\t.comm\t");
   assemble_name (stream, name);
-  fprintf (stream, ", " HOST_WIDE_INT_PRINT_DEC "\t" ASM_COMMENT_START
-	   " " HOST_WIDE_INT_PRINT_DEC "\n",
-	   rounded, size);
+  if (use_pe_aligned_common)
+    fprintf (stream, ", " HOST_WIDE_INT_PRINT_DEC ", %d\n",
+	   size ? size : (HOST_WIDE_INT) 1,
+	   exact_log2 (align) - exact_log2 (CHAR_BIT));
+  else
+    fprintf (stream, ", " HOST_WIDE_INT_PRINT_DEC "\t" ASM_COMMENT_START
+	   " " HOST_WIDE_INT_PRINT_DEC "\n", rounded, size);
 }
 
 /* The Microsoft linker requires that every function be marked as
diff --git a/gcc/configure b/gcc/configure
index 4bab41d..8a4f2c9 100755
--- a/gcc/configure
+++ b/gcc/configure
@@ -22631,6 +22631,44 @@ fi
   i[34567]86-*-* | x86_64-*-*)
     case $target_os in
       cygwin* | pe | mingw32*)
+	# Recent binutils allows the three-operand form of ".comm" on PE.  This
+	# definition is used unconditionally to initialise the default state of
+	# the target option variable that governs usage of the feature.
+	echo "$as_me:$LINENO: checking assembler for .comm with alignment" >&5
+echo $ECHO_N "checking assembler for .comm with alignment... $ECHO_C" >&6
+if test "${gcc_cv_as_comm_has_align+set}" = set; then
+  echo $ECHO_N "(cached) $ECHO_C" >&6
+else
+  gcc_cv_as_comm_has_align=no
+    if test $in_tree_gas = yes; then
+    if test $gcc_cv_gas_vers -ge `expr \( \( 2 \* 1000 \) + 19 \) \* 1000 + 52`
+  then gcc_cv_as_comm_has_align=yes
+fi
+  elif test x$gcc_cv_as != x; then
+    echo '.comm foo,1,32' > conftest.s
+    if { ac_try='$gcc_cv_as  -o conftest.o conftest.s >&5'
+  { (eval echo "$as_me:$LINENO: \"$ac_try\"") >&5
+  (eval $ac_try) 2>&5
+  ac_status=$?
+  echo "$as_me:$LINENO: \$? = $ac_status" >&5
+  (exit $ac_status); }; }
+    then
+	gcc_cv_as_comm_has_align=yes
+    else
+      echo "configure: failed program was" >&5
+      cat conftest.s >&5
+    fi
+    rm -f conftest.o conftest.s
+  fi
+fi
+echo "$as_me:$LINENO: result: $gcc_cv_as_comm_has_align" >&5
+echo "${ECHO_T}$gcc_cv_as_comm_has_align" >&6
+
+
+cat >>confdefs.h <<_ACEOF
+#define HAVE_GAS_ALIGNED_COMM `if test $gcc_cv_as_comm_has_align = yes; then echo 1; else echo 0; fi`
+_ACEOF
+
 	# Used for DWARF 2 in PE
 	echo "$as_me:$LINENO: checking assembler for .secrel32 relocs" >&5
 echo $ECHO_N "checking assembler for .secrel32 relocs... $ECHO_C" >&6
diff --git a/gcc/configure.ac b/gcc/configure.ac
index 80f9422..b5a1f7e 100644
--- a/gcc/configure.ac
+++ b/gcc/configure.ac
@@ -2954,6 +2954,15 @@ changequote(,)dnl
 changequote([,])dnl
     case $target_os in
       cygwin* | pe | mingw32*)
+	# Recent binutils allows the three-operand form of ".comm" on PE.  This
+	# definition is used unconditionally to initialise the default state of
+	# the target option variable that governs usage of the feature.
+	gcc_GAS_CHECK_FEATURE([.comm with alignment], gcc_cv_as_comm_has_align,
+	 [2,19,52],,[.comm foo,1,32])
+	AC_DEFINE_UNQUOTED(HAVE_GAS_ALIGNED_COMM,
+	  [`if test $gcc_cv_as_comm_has_align = yes; then echo 1; else echo 0; fi`],
+	  [Define if your assembler supports specifying the alignment
+	   of objects allocated using the GAS .comm command.])
 	# Used for DWARF 2 in PE
 	gcc_GAS_CHECK_FEATURE([.secrel32 relocs],
 	  gcc_cv_as_ix86_pe_secrel32,
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index db9df63..6a79566 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -15678,6 +15678,15 @@ This option is available for Cygwin and MinGW targets.  It
 specifies that a GUI application is to be generated by
 instructing the linker to set the PE header subsystem type
 appropriately.
+
+@item -mpe-aligned-commons
+@opindex mpe-aligned-commons
+This option is available for Cygwin and MinGW targets.  It
+specifies that the GNU extension to the PE file format that 
+permits the correct alignment of COMMON variables should be
+used when generating code.  It will be enabled by default if
+GCC detects that the target assembler found during configuration
+supports the feature.
 @end table
 
 See also under @ref{i386 and x86-64 Options} for standard options.
diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi
index 552d5c9..bc15583 100644
--- a/gcc/doc/tm.texi
+++ b/gcc/doc/tm.texi
@@ -7384,7 +7384,14 @@ outputting a single uninitialized variable.
 A C statement (sans semicolon) to output to the stdio stream
 @var{stream} the assembler definition of a common-label named
 @var{name} whose size is @var{size} bytes.  The variable @var{rounded}
-is the size rounded up to whatever alignment the caller wants.
+is the size rounded up to whatever alignment the caller wants.  It is
+possible that @var{size} may be zero, for instance if a struct with no
+other member than a zero-length array is defined.  In this case, the
+backend must output a symbol definition that allocates at least one
+byte, both so that the address of the resulting object does not compare
+equal to any other, and because some object formats cannot even express
+the concept of a zero-sized common symbol, as that is how they represent
+an ordinary undefined external.
 
 Use the expression @code{assemble_name (@var{stream}, @var{name})} to
 output the name itself; before and after that, output the additional
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 3e3c18e..3446982 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,15 @@
+2009-05-28  Dave Korn  <dave.korn.cygwin@gmail.com>
+            Uros Bizjak  <ubizjak@gmail.com>
+            Danny Smith  <dansmister@gmail.com>
+
+	PR target/37216
+
+	* lib/target-supports.exp (check_effective_target_pe_aligned_commons):
+	New function.
+	* gcc.target/i386/pr37216.c:  New test source file.
+	* gcc.dg/compat/struct-layout-1_generate.c (dg_options[]):  No longer
+	use -fno-common for testing Cygwin and MinGW targets.
+
 2009-05-28  Kai Tietz  <kai.tietz@onevision.com>
 
 	*  g++.dg/ext/packed6.C (size_t): Use __extension__ and
diff --git a/gcc/testsuite/gcc.dg/compat/struct-layout-1_generate.c b/gcc/testsuite/gcc.dg/compat/struct-layout-1_generate.c
index f563c27..4f5315d 100644
--- a/gcc/testsuite/gcc.dg/compat/struct-layout-1_generate.c
+++ b/gcc/testsuite/gcc.dg/compat/struct-layout-1_generate.c
@@ -46,7 +46,7 @@ const char *dg_options[] = {
 "/* { dg-options \"%s-I%s\" } */\n",
 "/* { dg-options \"%s-I%s -Wno-abi\" } */\n",
 "/* { dg-options \"%s-I%s -mno-mmx -Wno-abi\" { target i?86-*-* x86_64-*-* } } */\n",
-"/* { dg-options \"%s-I%s -fno-common\" { target hppa*-*-hpux* powerpc*-*-darwin* *-*-mingw32* *-*-cygwin* } } */\n",
+"/* { dg-options \"%s-I%s -fno-common\" { target hppa*-*-hpux* powerpc*-*-darwin* } } */\n",
 "/* { dg-options \"%s-I%s -mno-mmx -fno-common -Wno-abi\" { target i?86-*-darwin* x86_64-*-darwin* } } */\n",
 "/* { dg-options \"%s-I%s -mno-base-addresses\" { target mmix-*-* } } */\n",
 "/* { dg-options \"%s-I%s -mlongcalls -mtext-section-literals\" { target xtensa*-*-* } } */\n"
diff --git a/gcc/testsuite/gcc.target/i386/pr37216.c b/gcc/testsuite/gcc.target/i386/pr37216.c
new file mode 100644
index 0000000..5c847a7
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr37216.c
@@ -0,0 +1,17 @@
+/* { dg-do run } */
+/* { dg-options "-O3 -msse2" } */
+/* { dg-options "-O3 -msse2 -mpe-aligned-commons" { target pe_aligned_commons } } */
+
+#include "sse2-check.h"
+
+int iarr[64];
+int iint = 0;
+
+void
+sse2_test (void)
+{
+  int i;
+
+  for (i = 0; i < 64; i++)
+    iarr[i] = -2;
+}
diff --git a/gcc/testsuite/lib/target-supports.exp b/gcc/testsuite/lib/target-supports.exp
index f726e6f..e2d24c8 100644
--- a/gcc/testsuite/lib/target-supports.exp
+++ b/gcc/testsuite/lib/target-supports.exp
@@ -611,6 +611,18 @@ proc check_effective_target_pthread {} {
     } "-pthread"]
 }
 
+# Return 1 if compilation with -mpe-aligned-commons is error-free
+# for trivial code, 0 otherwise.
+
+proc check_effective_target_pe_aligned_commons {} {
+    if { [istarget *-*-cygwin*] || [istarget *-*-mingw*] } {
+	return [check_no_compiler_messages pe_aligned_commons object {
+	    int foo;
+	} "-mpe-aligned-commons"]
+    }
+    return 0
+}
+
 # Return 1 if the target supports -fstack-protector
 proc check_effective_target_fstack_protector {} {
     return [check_runtime fstack_protector {