[PATCH v2][MSP430] -Add fno-exceptions multilib

[Jozef Lawrynowicz <jozef dot l at mittosystems dot com>]

Original patch here: https://gcc.gnu.org/ml/gcc-patches/2019-11/msg00619.html

Late for stage 1 I know, but it's an iteration on a patch submitted before the
transition to stage 3 and the functional changes to the compiler are constrained
to the msp430 target.

The code size bloat added by building C++ programs using libraries containing
support for exceptions is significant. When using simple constructs such as
static variables, sometimes many kB from the libraries are unnecessarily
pulled in.

Since C++ libraries are built with exceptions enabled by default, there is
nothing the end user can do about this, even when they pass -fno-exceptions on
the command line.
So this patch adds a new -fno-exceptions multilib configuration for MSP430,
to reduce the code size linked executables when using C++ with -fno-exceptions.

Since building double the multilibs does significantly increase build time,
the patch also adds a configure option --disable-no-exceptions. This disables
the fno-exceptions multilibs from being built.

The changes from the original patch linked above are:
- Wrapped new gcc-dg-prune directives checking for disabled exception handling
  in an if statement, so they are only used if exception handling has been
  disabled in the global test configuration.
- Extended the spec strings used to check for when crt{begin,end}_no_eh.o can be
  used. When linking a C program where exceptions are implicitly disabled, 
  crt{begin,end}_no_eh.o can always be used unless -fexceptions is explicitly
  passed.

Successfully regtested for x86_64-pc-linux-gnu. There was no change in any of
the testresults (pass/fail/unsupported).

Regtested -fno-exceptions vs the default configuration for msp430-elf. There was
some fallout from exception handling tests not working, but nothing unexpected.

Ok to apply?

>From b74f34e5ae7f649296f7f6bcce35b75c34a2b0fd Mon Sep 17 00:00:00 2001
From: Jozef Lawrynowicz <jozef.l@mittosystems.com>
Date: Mon, 25 Nov 2019 12:07:24 +0000
Subject: [PATCH] MSP430: Add fno-exceptions multilib

ChangeLog:

2019-11-27  Jozef Lawrynowicz  <jozef.l@mittosystems.com>

	* config-ml.in: Support --disable-no-exceptions configure flag.

gcc/ChangeLog:

2019-11-27  Jozef Lawrynowicz  <jozef.l@mittosystems.com>

	* config/msp430/msp430.h (STARTFILE_SPEC) [!fexceptions]: Use
	crtbegin_no_eh.o if building for the C language.
	[fno-exceptions]: Use crtbegin_no_eh.o if building for any language
	except C.
	(ENDFILE_SPEC) [!fexceptions]: Use crtend_no_eh.o if building for 
	the C language.
	[fno-exceptions]: Use crtend_no_eh.o if building for any language
	except C.
	* config/msp430/t-msp430: Add -fno-exceptions multilib.
	* doc/install.texi: Document --disable-no-exceptions multilib configure
	option.

gcc/testsuite/ChangeLog:

2019-11-27  Jozef Lawrynowicz  <jozef.l@mittosystems.com>

	* lib/gcc-dg.exp: Add dg-prune messages for when exception handling is
	disabled.
	* lib/target-supports.exp (check_effective_target_exceptions_enabled):
	New.

libgcc/ChangeLog:

2019-11-27  Jozef Lawrynowicz  <jozef.l@mittosystems.com>

	* config.host: Add crt{begin,end}_no_eh.o to "extra_parts".
	* config/msp430/t-msp430: Add rules to build crt{begin,end}_no_eh.o.
---
 config-ml.in                          | 13 +++++++++++++
 gcc/config/msp430/msp430.h            | 11 +++++++++--
 gcc/config/msp430/t-msp430            |  9 +++++----
 gcc/doc/install.texi                  |  3 +++
 gcc/testsuite/lib/gcc-dg.exp          | 12 ++++++++++++
 gcc/testsuite/lib/target-supports.exp | 18 ++++++++++++++++++
 libgcc/config.host                    |  3 ++-
 libgcc/config/msp430/t-msp430         |  6 ++++++
 8 files changed, 68 insertions(+), 7 deletions(-)

diff --git a/config-ml.in b/config-ml.in
index 3e37f875c88..5720d38d23f 100644
--- a/config-ml.in
+++ b/config-ml.in
@@ -383,6 +383,19 @@ mips*-*-*)
 	  done
 	fi
 	;;
+msp430-*-*)
+	if [ x$enable_no_exceptions = xno ]
+	then
+	  old_multidirs="${multidirs}"
+	  multidirs=""
+	  for x in ${old_multidirs}; do
+	    case "$x" in
+	      *no-exceptions* ) : ;;
+	      *) multidirs="${multidirs} ${x}" ;;
+	    esac
+	  done
+	fi
+	;;
 powerpc*-*-* | rs6000*-*-*)
 	if [ x$enable_aix64 = xno ]
 	then
diff --git a/gcc/config/msp430/msp430.h b/gcc/config/msp430/msp430.h
index 0ea6b0a093e..7b94918a55d 100644
--- a/gcc/config/msp430/msp430.h
+++ b/gcc/config/msp430/msp430.h
@@ -44,13 +44,20 @@ extern bool msp430x;
     }						\
   while (0)
 
+/* For the "c" language where exceptions are implicitly disabled, use
+   crt*_no_eh.o unless -fexceptions is passed.  For other languages, only use
+   crt*_no_eh.o if -fno-exceptions is explicitly passed.  */
 #undef  STARTFILE_SPEC
 #define STARTFILE_SPEC "%{pg:gcrt0.o%s}" \
-  "%{!pg:%{minrt:crt0-minrt.o%s}%{!minrt:crt0.o%s}} %{!minrt:crtbegin.o%s}"
+  "%{!pg:%{minrt:crt0-minrt.o%s}%{!minrt:crt0.o%s}} " \
+  "%{!minrt:%{,c:%{!fexceptions:crtbegin_no_eh.o%s; :crtbegin.o%s}; " \
+    ":%{fno-exceptions:crtbegin_no_eh.o%s; :crtbegin.o%s}}}"
 
 /* -lgcc is included because crtend.o needs __mspabi_func_epilog_1.  */
 #undef  ENDFILE_SPEC
-#define ENDFILE_SPEC "%{!minrt:crtend.o%s} " \
+#define ENDFILE_SPEC \
+  "%{!minrt:%{,c:%{!fexceptions:crtend_no_eh.o%s; :crtend.o%s}; " \
+    ":%{fno-exceptions:crtend_no_eh.o%s; :crtend.o%s}}} " \
   "%{minrt:%:if-exists(crtn-minrt.o%s)}%{!minrt:%:if-exists(crtn.o%s)} -lgcc"
 
 #define ASM_SPEC "-mP " /* Enable polymorphic instructions.  */ \
diff --git a/gcc/config/msp430/t-msp430 b/gcc/config/msp430/t-msp430
index f8ba7751123..e180ce3efdb 100644
--- a/gcc/config/msp430/t-msp430
+++ b/gcc/config/msp430/t-msp430
@@ -28,8 +28,8 @@ msp430-devices.o: $(srcdir)/config/msp430/msp430-devices.c \
 
 # Enable multilibs:
 
-MULTILIB_OPTIONS    = mcpu=msp430 mlarge  mdata-region=none
-MULTILIB_DIRNAMES   = 430	   large  full-memory-range
+MULTILIB_OPTIONS    = mcpu=msp430 mlarge  mdata-region=none fno-exceptions
+MULTILIB_DIRNAMES   = 430	   large  full-memory-range no-exceptions
 
 # Match -mcpu=430
 MULTILIB_MATCHES    = mcpu?msp430=mcpu?430
@@ -41,9 +41,10 @@ MULTILIB_MATCHES   += mdata-region?none=mdata-region?either
 # hard-coded data here, because DRIVER_SELF_SPECS will place the correct
 # -mcpu option for a given mcu onto the command line.
 
-MULTILIB_REQUIRED = mcpu=msp430
-MULTILIB_REQUIRED += mlarge
+MULTILIB_REQUIRED =		    mcpu=msp430		       mlarge
+MULTILIB_REQUIRED += fno-exceptions mcpu=msp430/fno-exceptions mlarge/fno-exceptions
 MULTILIB_REQUIRED += mlarge/mdata-region=none
+MULTILIB_REQUIRED += mlarge/mdata-region=none/fno-exceptions
 
 
 MULTILIB_EXTRA_OPTS =
diff --git a/gcc/doc/install.texi b/gcc/doc/install.texi
index be203023da5..d926ca2e920 100644
--- a/gcc/doc/install.texi
+++ b/gcc/doc/install.texi
@@ -1086,6 +1086,9 @@ softfloat, m68881, m68000, m68020.
 @item mips*-*-*
 single-float, biendian, softfloat.
 
+@item msp430-*-*
+no-exceptions
+
 @item powerpc*-*-*, rs6000*-*-*
 aix64, pthread, softfloat, powercpu, powerpccpu, powerpcos, biendian,
 sysv, aix.
diff --git a/gcc/testsuite/lib/gcc-dg.exp b/gcc/testsuite/lib/gcc-dg.exp
index 1df645e283c..7396daa4a1d 100644
--- a/gcc/testsuite/lib/gcc-dg.exp
+++ b/gcc/testsuite/lib/gcc-dg.exp
@@ -417,6 +417,18 @@ proc gcc-dg-prune { system text } {
 	return "::unsupported::large return values"
     }
 
+    # If exceptions are disabled, mark tests expecting exceptions to be enabled
+    # as unsupported.
+    if { ![check_effective_target_exceptions_enabled] } {
+	if [regexp "(^|\n)\[^\n\]*: error: exception handling disabled" $text] {
+	    return "::unsupported::exception handling disabled"
+	}
+
+	if [regexp "(^|\n)\[^\n\]*: error: #error .__cpp_exceptions." $text] {
+	    return "::unsupported::exception handling disabled"
+	}
+    }
+
     return $text
 }
 
diff --git a/gcc/testsuite/lib/target-supports.exp b/gcc/testsuite/lib/target-supports.exp
index 5fe1e83492c..a5ced7980dc 100644
--- a/gcc/testsuite/lib/target-supports.exp
+++ b/gcc/testsuite/lib/target-supports.exp
@@ -8960,6 +8960,24 @@ proc check_effective_target_exceptions {} {
     return 1
 }
 
+# Used to check if the testing configuration supports exceptions.
+# Returns 0 if exceptions are unsupported or disabled (e.g. by passing
+# -fno-exceptions). Returns 1 if exceptions are enabled.
+proc check_effective_target_exceptions_enabled {} {
+    return [check_cached_effective_target exceptions_enabled {
+	if { [check_effective_target_exceptions] } {
+	    return [check_no_compiler_messages exceptions_enabled assembly {
+		void foo (void)
+		{
+		    throw 1;
+		}
+	    }]
+	} else {
+	    # If exceptions aren't supported, then they're not enabled.
+	    return 0
+	}
+    }]
+}
 
 proc check_effective_target_tiny {} {
     return [check_cached_effective_target tiny {
diff --git a/libgcc/config.host b/libgcc/config.host
index bc3e497739f..56868719fc8 100644
--- a/libgcc/config.host
+++ b/libgcc/config.host
@@ -1045,7 +1045,8 @@ moxie-*-elf | moxie-*-moxiebox* | moxie-*-uclinux* | moxie-*-rtems*)
 	;;
 msp430*-*-elf)
 	tmake_file="$tm_file t-crtstuff t-fdpbit msp430/t-msp430"
-        extra_parts="$extra_parts libmul_none.a libmul_16.a libmul_32.a libmul_f5.a"
+	extra_parts="$extra_parts crtbegin_no_eh.o crtend_no_eh.o"
+	extra_parts="$extra_parts libmul_none.a libmul_16.a libmul_32.a libmul_f5.a"
 	;;
 nds32*-linux*)
 	# Basic makefile fragment and extra_parts for crt stuff.
diff --git a/libgcc/config/msp430/t-msp430 b/libgcc/config/msp430/t-msp430
index 17d85b6cb23..72ae93a8dae 100644
--- a/libgcc/config/msp430/t-msp430
+++ b/libgcc/config/msp430/t-msp430
@@ -42,6 +42,12 @@ LIB2ADD = \
 
 HOST_LIBGCC2_CFLAGS += -Os -ffunction-sections -fdata-sections -mhwmult=none
 
+crtbegin_no_eh.o: $(srcdir)/crtstuff.c
+	$(crt_compile) -U__LIBGCC_EH_FRAME_SECTION_NAME__ -c $< -DCRT_BEGIN
+
+crtend_no_eh.o: $(srcdir)/crtstuff.c
+	$(crt_compile) -U__LIBGCC_EH_FRAME_SECTION_NAME__ -c $< -DCRT_END
+
 mpy.o: $(srcdir)/config/msp430/mpy.c
 	$(gcc_compile) $< -c
 
-- 
2.17.1