bugpoint: disabling symbolication of bugpoint-executed programs

Initial implementation - needs similar work/testing for other tools
bugpoint invokes (llc, lli I think, maybe more).

Alternatively (as suggested by chandlerc@) an environment variable could
be used. This would allow the option to pass transparently through user
scripts, pass to compilers if they happened to be LLVM-ish, etc.

I worry a bit about using cl::opt in the crash handling code - LLVM
might crash early, perhaps before the cl::opt is properly initialized?
Or at least before arguments have been parsed?

 - should be OK since it defaults to "pretty", so if the crash is very
 early in opt parsing, etc, then crash reports will still be symbolized.

I shyed away from doing this with an environment variable when I
realized that would require copying the existing environment and
appending the env variable of interest. But it seems there's no existing
LLVM API for accessing the environment (even the Support tests for
process launching have their own ifdefs for getting the environment). It
could be added, but seemed like a higher bar/untested codepath to
actually add environment variables.

Most importantly, this reduces the runtime of test/BugPoint/metadata.ll
in a split-dwarf Debug build from 1m34s to 6.5s by avoiding a lot of
symbolication. (this wasn't a problem for non-split-dwarf builds only
because the executable was too large to map into memory (due to bugpoint
setting a 400MB memory (including address space - not sure why? Going to
remove that) limit on the child process) so symbolication would fail
fast & wouldn't spend all that time parsing DWARF, etc)

Reviewers: chandlerc, dannyb

Differential Revision: https://reviews.llvm.org/D33804

llvm-svn: 305056

llvm/lib/Support/Signals.cpp

@@ -26,15 +26,21 @@
 #include "llvm/Support/Program.h"
 #include "llvm/Support/StringSaver.h"
 #include "llvm/Support/raw_ostream.h"
+#include "llvm/Support/Options.h"
 #include <vector>
 
-namespace llvm {
-
 //===----------------------------------------------------------------------===//
 //=== WARNING: Implementation here must contain only TRULY operating system
 //===          independent code.
 //===----------------------------------------------------------------------===//
 
+using namespace llvm;
+
+static cl::opt<bool>
+    DisableSymbolication("disable-symbolication",
+                         cl::desc("Disable symbolizing crash backtraces."),
+                         cl::init(false), cl::Hidden);
+
 static ManagedStatic<std::vector<std::pair<void (*)(void *), void *>>>
     CallBacksToRun;
 void sys::RunSignalHandlers() {
@@ -44,9 +50,6 @@ void sys::RunSignalHandlers() {
     I.first(I.second);
   CallBacksToRun->clear();
 }
-}
-
-using namespace llvm;
 
 static bool findModulesAndOffsets(void **StackTrace, int Depth,
                                   const char **Modules, intptr_t *Offsets,
@@ -70,6 +73,9 @@ static bool printSymbolizedStackTrace(StringRef Argv0,
 static bool printSymbolizedStackTrace(StringRef Argv0,
                                       void **StackTrace, int Depth,
                                       llvm::raw_ostream &OS) {
+  if (DisableSymbolication)
+    return false;
+
   // Don't recursively invoke the llvm-symbolizer binary.
   if (Argv0.find("llvm-symbolizer") != std::string::npos)
     return false;

llvm/test/BugPoint/unsymbolized.ll

@@ -0,0 +1,21 @@
+; REQUIRES: loadable_module
+; RUN: echo "import sys" > %t.py
+; RUN: echo "print('args = ' + str(sys.argv))" >> %t.py
+; RUN: echo "exit(1)" >> %t.py
+; RUN: not bugpoint -load %llvmshlibdir/BugpointPasses%shlibext %s -output-prefix %t -bugpoint-crashcalls -opt-command="%python" -opt-args %t.py | FileCheck %s
+; RUN: not --crash opt -load %llvmshlibdir/BugpointPasses%shlibext %s -bugpoint-crashcalls -disable-symbolication 2>&1 | FileCheck --check-prefix=CRASH %s
+
+; Test that bugpoint disables symbolication on the opt tool to reduce runtime overhead when opt crashes
+; CHECK: args = {{.*}}'-disable-symbolication'
+
+; Test that opt, when it crashes & is passed -disable-symbolication, doesn't symbolicate.
+; In theory this test should maybe be in test/tools/opt or
+; test/Transforms, but since there doesn't seem to be another convenient way to
+; crash opt, apart from the BugpointPasses dynamic plugin, this is the spot for
+; now.
+; CRASH-NOT: Signals.inc
+
+define void @f() {
+  call void @f()
+  ret void
+}

llvm/tools/bugpoint/OptimizerDriver.cpp

@@ -202,10 +202,11 @@ bool BugDriver::runPasses(Module *Program,
   } else
     Args.push_back(tool.c_str());
 
-  Args.push_back("-o");
-  Args.push_back(OutputFilename.c_str());
   for (unsigned i = 0, e = OptArgs.size(); i != e; ++i)
     Args.push_back(OptArgs[i].c_str());
+  Args.push_back("-disable-symbolication");
+  Args.push_back("-o");
+  Args.push_back(OutputFilename.c_str());
   std::vector<std::string> pass_args;
   for (unsigned i = 0, e = PluginLoader::getNumPlugins(); i != e; ++i) {
     pass_args.push_back(std::string("-load"));