Fix gdb.base/align-*.exp and Clang + LTO and AIX GCC

Clang with LTO (clang -flto) garbage collects unused global variables,
Thus, gdb.base/align-c.exp and gdb.base/align-c++.exp fail with
hundreds of FAILs like so:

 $ make check \
    TESTS="gdb.*/align-*.exp" \
    RUNTESTFLAGS="CC_FOR_TARGET='clang -flto' CXX_FOR_TARGET='clang++ -flto'"
 ...
 FAIL: gdb.base/align-c.exp: get integer valueof "a_char"
 FAIL: gdb.base/align-c.exp: print _Alignof(char)
 FAIL: gdb.base/align-c.exp: get integer valueof "a_char_x_char"
 FAIL: gdb.base/align-c.exp: print _Alignof(struct align_pair_char_x_char)
 FAIL: gdb.base/align-c.exp: get integer valueof "a_char_x_unsigned_char"
 ...

AIX GCC has the same issue, and there the easier way of adding
__attribute__((used)) to globals does not help.

So add explicit uses of all globals to the generated code.

For the C++ test, that reveals that the static variable members of the
generated structs are not defined anywhere, leading to undefined
references.  Fixed by emitting initialization for all static members.

Lastly, I noticed that CXX_FOR_TARGET was being ignored -- that's
because the align-c++.exp testcase is compiling with the C compiler
driver.  Fixed by passing "c++" as option to prepare_for_testing.

Change-Id: I874b717afde7b6fb1e45e526912b518a20a12716

1 files changed, 47 insertions, 2 deletions

diff --git a/gdb/testsuite/gdb.base/align.exp.tcl b/gdb/testsuite/gdb.base/align.exp.tcl
index 6a75a14..550afe1 100644
--- a/gdb/testsuite/gdb.base/align.exp.tcl
+++ b/gdb/testsuite/gdb.base/align.exp.tcl
@@ -94,12 +94,15 @@ proc prepare_test_source_file { lang } {
 		puts $outfile "DEF_WITH_1_STATIC ($utype, $uinner);"
 		set joined "static_${utype}_x_${uinner}"
 		puts $outfile "struct align_pair_$joined item_${joined};"
+		puts $outfile "$utype align_pair_${joined}::one = 0;"
 		puts $outfile "unsigned a_${joined}"
 		puts $outfile "  = ${align_func} (struct align_pair_${joined});"
 
 		puts $outfile "DEF_WITH_2_STATIC ($utype, $uinner);"
 		set joined "static_${utype}_x_static_${uinner}"
 		puts $outfile "struct align_pair_$joined item_${joined};"
+		puts $outfile "$utype align_pair_${joined}::one = 0;"
+		puts $outfile "$uinner align_pair_${joined}::two = 0;"
 		puts $outfile "unsigned a_${joined}"
 		puts $outfile "  = ${align_func} (struct align_pair_${joined});"
 	    }
@@ -107,12 +110,53 @@ proc prepare_test_source_file { lang } {
     }
 
     # Epilogue.
-    puts $outfile {
+    puts $outfile "
 	int main() {
-	    return 0;
+    "
+
+    # Clang with LTO garbage collects unused global variables, even at
+    # -O0.  Likewise AIX GCC.  Add uses to all global variables to
+    # prevent it.
+
+    if { $lang == "c" } {
+	puts $outfile "a_void++;"
+    }
+
+    # First, add uses for single items.
+    foreach type $typelist {
+	set utype [join [split $type] _]
+	puts $outfile "item_$utype++;"
+	if { $lang == "c" } {
+	    puts $outfile "a_$utype++;"
+	}
+    }
+
+    # Now add uses for all pairs.
+    foreach type $typelist {
+	set utype [join [split $type] _]
+	foreach inner $typelist {
+	    set uinner [join [split $inner] _]
+	    set joined "${utype}_x_${uinner}"
+	    puts $outfile "item_${joined}.one++;"
+	    puts $outfile "a_${joined}++;"
+
+	    if { $lang == "c++" } {
+		set joined "static_${utype}_x_${uinner}"
+		puts $outfile "item_${joined}.one++;"
+		puts $outfile "a_${joined}++;"
+
+		set joined "static_${utype}_x_static_${uinner}"
+		puts $outfile "item_${joined}.one++;"
+		puts $outfile "a_${joined}++;"
+	    }
 	}
     }
 
+    puts $outfile "
+	    return 0;
+	}
+    "
+
     close $outfile
 
     return $filename
@@ -127,6 +171,7 @@ proc run_alignment_test { lang } {
 
     set flags {debug}
     if { "$lang" == "c++" } {
+	lappend flags "c++"
 	lappend flags "additional_flags=-std=c++11"
     }
     standard_testfile $filename