[pushed] Disable gdb.ada/dgopt.exp with gnat-llvm

[Tom Tromey <tromey@adacore.com>]

gdb.ada/dgopt.exp fails with gnat-llvm.

Looking into it, it turns out that this test case relies on a bug in
GNAT.  In particular, despite the use of -gnatDG, GNAT will still put
a reference to "x.adb" into both the DWARF .debug_info and into the
line table.  The test relies on this, because the original problem
being fixed here is that, when the test was written, there was a bug
causing these references to be dropped when writing .debug_names.

gnat-llvm does not have this same bug -- it only emits references to
x.adb.dg.

This patch disables this test for gnat-llvm.  There's not really a
good way to tell that gnatmake is llvm-based, so while I've added a
new caching proc for this, it is just a proxy for an existing proc.

Since this only affects gnat-llvm, and was discussed internally, I am
going to check it in.
---
 gdb/testsuite/gdb.ada/dgopt.exp | 8 ++++++++
 gdb/testsuite/lib/ada.exp       | 8 ++++++++
 2 files changed, 16 insertions(+)

diff --git a/gdb/testsuite/gdb.ada/dgopt.exp b/gdb/testsuite/gdb.ada/dgopt.exp
index 9e8e8a676a8..831aa053f36 100644
--- a/gdb/testsuite/gdb.ada/dgopt.exp
+++ b/gdb/testsuite/gdb.ada/dgopt.exp
@@ -19,6 +19,14 @@ load_lib "ada.exp"
 
 require allow_ada_tests
 
+# Despite appearances, this is not really an "Ada" test -- instead the
+# scenario here is that GNAT ends up putting one reference to x.adb
+# into the DWARF (whereas it mostly refers to x.adb.dg); and this
+# reference was being incorrectly omitted from .debug_names.
+# gnat-llvm does not have this bug, so the test does not make sense
+# there.
+require !using_gnat_llvm
+
 standard_ada_testfile x
 
 if {[gdb_compile_ada "${srcfile}" "${binfile}" executable \
diff --git a/gdb/testsuite/lib/ada.exp b/gdb/testsuite/lib/ada.exp
index 8c9821bb897..e20b35c8ebe 100644
--- a/gdb/testsuite/lib/ada.exp
+++ b/gdb/testsuite/lib/ada.exp
@@ -292,6 +292,14 @@ gdb_caching_proc ada_minimal_encodings {} {
 		additional_flags=-fgnat-encodings=minimal]
 }
 
+# Return 1 if GNAT is based on LLVM.
+gdb_caching_proc using_gnat_llvm {} {
+    # Whether or not gnatmake will use LLVM can't be determined from
+    # the command line -- e.g., --version doesn't provide any
+    # indication.  So for now use a proxy.
+    return [expr {![ada_minimal_encodings]}]
+}
+
 # Return 1 if GNAT supports -Og.
 gdb_caching_proc ada_og {} {
     return [ada_simple_compile gnat_og additional_flags=-Og]

base-commit: 108db853326a1335fadb6d0ad9955dd7714b1ce1
-- 
2.54.0