[llvm-reduce] make llvm-reduce save the best reduction it has when it crashes

[Tyker]

Summary

This helps with both debugging llvm-reduce and sometimes getting usefull result even if llvm-reduce crashes

[lebedev.ri]

1. I'm pretty sure it's not okay to allocate memory in crash handler.
2. We can't know that the internal state is still consistent.

We already store each IR to disk to run the interestingness test on it.
Instead of LastIntersting = ReducedProgram.get();, let's just rewrite the OutputFilename each time.

[Tyker]

In D85996#2219124, @lebedev.ri wrote:

1. I'm pretty sure it's not okay to allocate memory in crash handler.
2. We can't know that the internal state is still consistent.

i agree with both points but all i was trying to do i salvage what can be salvaged.

We already store each IR to disk to run the interestingness test on it.
Instead of LastIntersting = ReducedProgram.get();, let's just rewrite the OutputFilename each time.

yeah this is a better idea.

[lebedev.ri]

This seems fine to me, thanks.
If you have llvm-reduce crashers, do let me know, i'm interested.

llvm/tools/llvm-reduce/llvm-reduce.cpp

84–87

I wonder if we want do to something special if input == output?

[Tyker]

In D85996#2219650, @lebedev.ri wrote:

This seems fine to me, thanks.
If you have llvm-reduce crashers, do let me know, i'm interested.

i had one but i has been fixed by 6187eeb683d8c639282d437e6af585e9b7f9c93e.

llvm/tools/llvm-reduce/llvm-reduce.cpp

84–87

we could save the original into its original name plus some post-fix like .old before overwriting.

llvm/tools/llvm-reduce/deltas/Delta.cpp

 #include "llvm/ADT/STLExtras.h"
 #include "llvm/Support/ToolOutputFile.h"
 #include "llvm/Transforms/Utils/Cloning.h"
 #include <fstream>
 #include <set>
 
 using namespace llvm;
 
+void writeOutput(llvm::Module *M, llvm::StringRef Message);
+
 bool IsReduced(Module &M, TestRunner &Test, SmallString<128> &CurrentFilepath) {
   // Write Module to tmp file
   int FD;
   std::error_code EC =
       sys::fs::createTemporaryFile("llvm-reduce", "ll", FD, CurrentFilepath);
   if (EC) {
     errs() << "Error making unique filename: " << EC.message() << "!\n";
     exit(1);
for (Chunk &ChunkToCheckForUninterestingness :
         errs() << "\n";
         continue;
       }
 
       FoundAtLeastOneNewUninterestingChunkWithCurrentGranularity = true;
       UninterestingChunks.insert(ChunkToCheckForUninterestingness);
       ReducedProgram = std::move(Clone);
       errs() << " **** SUCCESS | lines: " << getLines(CurrentFilepath) << "\n";
+      writeOutput(ReducedProgram.get(), "Saved new best reduction to ");
     }
     // Delete uninteresting chunks
     erase_if(ChunksStillConsideredInteresting,
              [&UninterestingChunks](const Chunk &C) {
                return UninterestingChunks.count(C);
              });
   } while (!ChunksStillConsideredInteresting.empty() &&
            (FoundAtLeastOneNewUninterestingChunkWithCurrentGranularity ||
             increaseGranularity(ChunksStillConsideredInteresting)));
 
   // If we reduced the testcase replace it
   if (ReducedProgram)
     Test.setProgram(std::move(ReducedProgram));
   errs() << "Couldn't increase anymore.\n";
 }

llvm/tools/llvm-reduce/llvm-reduce.cpp

static std::unique_ptr<Module> parseInputFile(StringRef Filename,
   if (verifyModule(*Result, &errs())) {
     errs() << "Error: " << Filename << " - input module is broken!\n";
     return std::unique_ptr<Module>();
   }
 
   return Result;
 }
 
+void writeOutput(Module *M, StringRef Message) {
+  if (ReplaceInput) // In-place
+    OutputFilename = InputFilename.c_str();
+  else if (OutputFilename.empty() || OutputFilename == "-")
+    OutputFilename = "reduced.ll";
+
+  std::error_code EC;
+  raw_fd_ostream Out(OutputFilename, EC);
+  if (EC) {
+    errs() << "Error opening output file: " << EC.message() << "!\n";
+    exit(1);
+  }
+  M->print(Out, /*AnnotationWriter=*/nullptr);
+  errs() << Message << OutputFilename << "\n";
+}
+
 int main(int argc, char **argv) {
   InitLLVM X(argc, argv);
 
   cl::ParseCommandLineOptions(argc, argv, "LLVM automatic testcase reducer.\n");
 
   LLVMContext Context;
   std::unique_ptr<Module> OriginalProgram =
       parseInputFile(InputFilename, Context);
 
   // Initialize test environment
   TestRunner Tester(TestFilename, TestArguments);
   Tester.setProgram(std::move(OriginalProgram));
 
   // Try to reduce code
   runDeltaPasses(Tester);
 
   if (!Tester.getProgram()) {
     errs() << "\nCouldnt reduce input :/\n";
   } else {
     // Print reduced file to STDOUT
     if (OutputFilename == "-")
       Tester.getProgram()->print(outs(), nullptr);
-    else {
-      if (ReplaceInput) // In-place
-        OutputFilename = InputFilename.c_str();
-      else if (OutputFilename.empty())
-        OutputFilename = "reduced.ll";
-
-      std::error_code EC;
-      raw_fd_ostream Out(OutputFilename, EC);
-      if (EC) {
-        errs() << "Error opening output file: " << EC.message() << "!\n";
-        exit(1);
-      }
-      Tester.getProgram()->print(Out, /*AnnotationWriter=*/nullptr);
-      errs() << "\nDone reducing! Reduced testcase: " << OutputFilename << "\n";
-    }
+    else
+      writeOutput(Tester.getProgram(), "\nDone reducing! Reduced testcase: ");
   }
 
   return 0;
 }