[lld] Add test suite mode for running LLD main twice

[smeenai]

Summary

LLD_IN_TEST determines how many times each port's main function is
run in each LLD process, and setting LLD_IN_TEST=2 (or higher) is useful
for checking if we're cleaning up and resetting global state correctly.
Add a test suite parameter to enable this easily. There's work in
progress to remove global state (e.g. D108850), but this seems useful in
the interim.

[smeenai]

Use XFAIL instead of unsupported, so that we get notified if the behavior changes

[rnk]

lgtm

lld/test/MachO/error-limit.test

+## We're intentionally testing fatal errors, which isn't supported for testing
+## when main is run twice.
+XFAIL: main-run-twice
+
 ## Check that we only see 20 (the default error-limit) "cannot open" errors
 RUN: not %lld A B C D E F G H I J K L M N O P Q R S T U V W X Y Z 2>&1 | \
 RUN:     FileCheck -check-prefix=DEFAULT %s
 
 DEFAULT:      cannot open A:
 DEFAULT:      cannot open T:
 DEFAULT-NOT:  cannot open U:
 DEFAULT-NEXT: too many errors emitted, stopping now (use --error-limit=0 to see all errors)

lld/test/MachO/invalid/bad-archive.s

+## We're intentionally testing fatal errors (for malformed input files), and
+## fatal errors aren't supported for testing when main is run twice.
+# XFAIL: main-run-twice
+
 # REQUIRES: x86
 # RUN: echo "!<arch>" > %t.a
 # RUN: echo "foo" >> %t.a
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %s -o %t.o
 
 # RUN: not %lld %t.o %t.a -o /dev/null 2>&1 | FileCheck -DFILE=%t.a %s
 # RUN: not %lld %t.o -force_load %t.a -o /dev/null 2>&1 | FileCheck -DFILE=%t.a %s
 # RUN: not %lld %t.o -ObjC %t.a -o /dev/null 2>&1 | FileCheck -DFILE=%t.a %s
 # CHECK: error: [[FILE]]: failed to parse archive: truncated or malformed archive (remaining size of archive too small for next archive member header at offset 8)
 
 .global _main
 _main:
   ret

lld/test/MachO/invalid/cstring-dedup.s

+## We're intentionally testing fatal errors (for malformed input files), and
+## fatal errors aren't supported for testing when main is run twice.
+# XFAIL: main-run-twice
+
 # REQUIRES: x86
 # RUN: rm -rf %t; split-file %s %t
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %t/not-terminated.s -o %t/not-terminated.o
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %t/relocs.s -o %t/relocs.o
 
 # RUN: not %lld -dylib --deduplicate-literals %t/not-terminated.o 2>&1 | FileCheck %s --check-prefix=TERM
 # RUN: not %lld -dylib --deduplicate-literals %t/relocs.o 2>&1 | FileCheck %s --check-prefix=RELOCS
 

lld/test/MachO/invalid/lto-bitcode-nodatalayout.ll

+;; We're intentionally testing fatal errors (for malformed input files), and
+;; fatal errors aren't supported for testing when main is run twice.
+; XFAIL: main-run-twice
+
 ; REQUIRES: x86
 ; RUN: llvm-as %s -o %t.o
 ; RUN: not %lld %t.o -o /dev/null 2>&1 | FileCheck %s
 
 ; CHECK: error: input module has no datalayout
 
 ; This bitcode file has no datalayout.
 ; Check that we error out producing a reasonable diagnostic.
 target triple = "x86_64-apple-macosx10.15.0"
 
 define void @_start() {
   ret void
 }

lld/test/MachO/invalid/reserved-section-name.s

+## We're intentionally testing fatal errors (for malformed input files), and
+## fatal errors aren't supported for testing when main is run twice.
+# XFAIL: main-run-twice
+
 # REQUIRES: x86
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %s -o %t.o
 # RUN: not %lld -o %t %t.o 2>&1 | FileCheck %s -DFILE=%t.o
 # CHECK: error: section from [[FILE]] conflicts with synthetic section __DATA_CONST,__got
 
 .globl _main
 
 .section __DATA_CONST,__got

lld/test/MachO/time-trace.s

+## When running main twice, we'll also output the time trace JSON twice, which
+## breaks JSON parsing.
+# XFAIL: main-run-twice
+
 # REQUIRES: x86
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %s -o %t.o
 
 ## Test implicit trace file name
 # RUN: %lld --time-trace --time-trace-granularity=0 -o %t1.macho %t.o
 # RUN: cat %t1.macho.time-trace \
 # RUN:   | %python -c 'import json, sys; json.dump(json.loads(sys.stdin.read()), sys.stdout, sort_keys=True, indent=2)' \
 # RUN:   | FileCheck %s

lld/test/lit.cfg.py

('--targets-built', {'AArch64': 'aarch64',
                           'RISCV': 'riscv',
                           'Sparc': 'sparc',
                           'WebAssembly': 'wasm',
                           'X86': 'x86'})
      ])
 
 # Set a fake constant version so that we get consistent output.
 config.environment['LLD_VERSION'] = 'LLD 1.0'
+
+# LLD_IN_TEST determines how many times `main` is run inside each process, which
+# lets us test that it's cleaning up after itself and resetting global state
+# correctly (which is important for usage as a library).
+run_lld_main_twice = lit_config.params.get('RUN_LLD_MAIN_TWICE', False)
+if not run_lld_main_twice:
     config.environment['LLD_IN_TEST'] = '1'
+else:
+    config.environment['LLD_IN_TEST'] = '2'
+    # Many ELF tests fail in this mode.
+    config.excludes.append('ELF')
+    # Some old Mach-O backend tests fail, and it's due for removal anyway.
+    config.excludes.append('mach-o')
+    # Some new Mach-O backend tests fail; give them a way to mark themselves
+    # unsupported in this mode.
+    config.available_features.add('main-run-twice')
 
 # Indirectly check if the mt.exe Microsoft utility exists by searching for
 # cvtres, which always accompanies it.  Alternatively, check if we can use
 # libxml2 to merge manifests.
 if (lit.util.which('cvtres', config.environment['PATH']) or
         config.have_libxml2):
     config.available_features.add('manifest_tool')