[gcc r12-8484] Darwin: Fix empty g++ command lines [PR105599].

[gcc r12-8484] Darwin: Fix empty g++ command lines [PR105599].

[Iain D Sandoe]

https://gcc.gnu.org/g:58c0bc2b62cdbbe9d9677b448fe52a8c54044276

commit r12-8484-g58c0bc2b62cdbbe9d9677b448fe52a8c54044276
Author: Iain Sandoe <iain@sandoe.co.uk>
Date:   Sun May 29 16:14:32 2022 +0100

    Darwin: Fix empty g++ command lines [PR105599].
    
    An empty g++ command line should produce a diagnostic that there are no
    inputs.  The PR is that currently Darwin produces a dignostic about missing
    link items instead - this is because (errnoeously), for this driver, we are
    creating a link job for empty command lines.
    
    The problem occurs in four stages:
    
     The g++ driver appends -shared-libgcc to the command line.
    
     The Darwin driver_init code in the backend does not see this (it sees an
     empty command line).
    
     When the back end driver code driver sees an empty command line, it does not
     add any supplementary flags (e.g. asm-macosx-version-min) - precisely to
     avoid anything being claimed as an input_file and therefore triggering a link
     line.
    
     Since we do not have a value for asm-macosx-version-min when processing the
     driver specs, we unconditionally inject 'multiply_defined suppress' which is
     used with shared libgcc (but only intended on very old Darwin).  This then
     causes the generation of a link job.
    
    The solution, for the present, is to move version-specific link params to the
    LINK_SPEC so that they are only processed when a link job has already been
    decided.
    
    Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>
    
            PR target/105599
    
    gcc/ChangeLog:
    
            * config/darwin.h: Move versions-specific handling of multiply_defined
            from SUBTARGET_DRIVER_SELF_SPECS to LINK_SPEC.
    
    (cherry picked from commit 794737976b9a6418eab817f143bb4eb2d0c834d2)

Diff:
---
 gcc/config/darwin.h | 17 ++++++-----------
 1 file changed, 6 insertions(+), 11 deletions(-)

diff --git a/gcc/config/darwin.h b/gcc/config/darwin.h
index 3682bd2b2c5..51e257dc698 100644
--- a/gcc/config/darwin.h
+++ b/gcc/config/darwin.h
@@ -143,10 +143,7 @@ extern GTY(()) int darwin_ms_struct;
    Right now there's no mechanism to split up the "variable portion" (%*) of
    the matched spec string, so where we have some driver specs that take 2
    or 3 arguments, these cannot be processed here, but are deferred until the
-   LINK_SPEC, where they are copied verbatim.
-   We have a "safe" version of the MacOS version string, that's been sanity-
-   checked and truncated to minor version.  If the 'tiny' (3rd) portion of the
-   value is not significant, it's better to use this in version-compare().  */
+   LINK_SPEC, where they are copied verbatim.  */
 
 #undef SUBTARGET_DRIVER_SELF_SPECS
 #define SUBTARGET_DRIVER_SELF_SPECS					\
@@ -220,13 +217,8 @@ extern GTY(()) int darwin_ms_struct;
   "%{image_base*:-Xlinker -image_base -Xlinker %*} %<image_base*",	\
   "%{init*:-Xlinker -init -Xlinker %*} %<init*",			\
   "%{multi_module:-Xlinker -multi_module} %<multi_module",		\
-  "%{multiply_defined*:-Xlinker -multiply_defined -Xlinker %*; \
-     :%{shared-libgcc: \
-       %:version-compare(< 10.5 asm_macosx_version_min= -Xlinker) \
-       %:version-compare(< 10.5 asm_macosx_version_min= -multiply_defined) \
-       %:version-compare(< 10.5 asm_macosx_version_min= -Xlinker) \
-       %:version-compare(< 10.5 asm_macosx_version_min= suppress)}} \
-     %<multiply_defined*",						\
+  "%{multiply_defined*:-Xlinker -multiply_defined -Xlinker %*} \
+     %<multiply_defined* ",						\
   "%{multiplydefinedunused*:\
      -Xlinker -multiply_defined_unused -Xlinker %*} \
      %<multiplydefinedunused* ",					\
@@ -458,6 +450,9 @@ extern GTY(()) int darwin_ms_struct;
    %{!force_cpusubtype_ALL:-arch %(darwin_subarch)} "\
    LINK_SYSROOT_SPEC \
   "%{mmacosx-version-min=*:-macosx_version_min %*} \
+   %{!multiply_defined*:%{shared-libgcc: \
+     %:version-compare(< 10.5 mmacosx-version-min= -multiply_defined) \
+     %:version-compare(< 10.5 mmacosx-version-min= suppress) }} \
    %{sectalign*} %{sectcreate*} %{sectobjectsymbols*}  %{sectorder*} \
    %{segaddr*} %{segcreate*} %{segprot*} "