From 04464cf7313a7c2873f2b8a9011a19f1685b44c1 Mon Sep 17 00:00:00 2001
From: Keno Fischer <kfischer@college.harvard.edu>
Date: Fri, 4 Dec 2015 21:56:46 +0000
Subject: [llc/opt] Add an option to run all passes twice

Summary: Lately, I have submitted a number of patches to fix bugs that
only occurred when using the same pass manager to compile multiple
modules (generally these bugs are failure to reset some persistent
state). Unfortunately I don't think there is currently a way to test
that from the command line. This adds a very simple flag to both llc
and opt, under which the tools will simply re-run their respective
pass pipelines using the same pass manager on (a clone of the same
module). Additionally, we verify that both outputs are bitwise the
same.

Reviewers: yaron.keren

Subscribers: loladiro, yaron.keren, kcc, llvm-commits

Differential Revision: http://reviews.llvm.org/D14965

llvm-svn: 254774
---
 llvm/tools/opt/opt.cpp | 48 +++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 43 insertions(+), 5 deletions(-)

(limited to 'llvm/tools/opt/opt.cpp')

diff --git a/llvm/tools/opt/opt.cpp b/llvm/tools/opt/opt.cpp
index 5fe2f034c6e..c1510a7fb25 100644
--- a/llvm/tools/opt/opt.cpp
+++ b/llvm/tools/opt/opt.cpp
@@ -28,6 +28,7 @@
 #include "llvm/IR/DebugInfo.h"
 #include "llvm/IR/IRPrintingPasses.h"
 #include "llvm/IR/LLVMContext.h"
+#include "llvm/IR/LegacyPassManager.h"
 #include "llvm/IR/LegacyPassNameParser.h"
 #include "llvm/IR/Module.h"
 #include "llvm/IR/Verifier.h"
@@ -36,7 +37,6 @@
 #include "llvm/LinkAllIR.h"
 #include "llvm/LinkAllPasses.h"
 #include "llvm/MC/SubtargetFeature.h"
-#include "llvm/IR/LegacyPassManager.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/Host.h"
@@ -51,6 +51,7 @@
 #include "llvm/Support/ToolOutputFile.h"
 #include "llvm/Target/TargetMachine.h"
 #include "llvm/Transforms/IPO/PassManagerBuilder.h"
+#include "llvm/Transforms/Utils/Cloning.h"
 #include <algorithm>
 #include <memory>
 using namespace llvm;
@@ -190,6 +191,11 @@ static cl::opt<bool> PreserveAssemblyUseListOrder(
     cl::desc("Preserve use-list order when writing LLVM assembly."),
     cl::init(false), cl::Hidden);
 
+static cl::opt<bool>
+    RunTwice("run-twice",
+             cl::desc("Run all passes twice, re-using the same pass manager."),
+             cl::init(false), cl::Hidden);
+
 static inline void addPass(legacy::PassManagerBase &PM, Pass *P) {
   // Add the pass to the pass manager...
   PM.add(P);
@@ -582,14 +588,25 @@ int main(int argc, char **argv) {
   if (!NoVerify && !VerifyEach)
     Passes.add(createVerifierPass());
 
+  // In run twice mode, we want to make sure the output is bit-by-bit
+  // equivalent if we run the pass manager again, so setup two buffers and
+  // a stream to write to them. Note that llc does something similar and it
+  // may be worth to abstract this out in the future.
+  SmallVector<char, 0> Buffer;
+  SmallVector<char, 0> CompileTwiceBuffer;
+  std::unique_ptr<raw_svector_ostream> BOS;
+  raw_ostream *OS = &Out->os();
+  if (RunTwice) {
+    BOS = make_unique<raw_svector_ostream>(Buffer);
+    OS = BOS.get();
+  }
+
   // Write bitcode or assembly to the output as the last step...
   if (!NoOutput && !AnalyzeOnly) {
     if (OutputAssembly)
-      Passes.add(
-          createPrintModulePass(Out->os(), "", PreserveAssemblyUseListOrder));
+      Passes.add(createPrintModulePass(*OS, "", PreserveAssemblyUseListOrder));
     else
-      Passes.add(
-          createBitcodeWriterPass(Out->os(), PreserveBitcodeUseListOrder));
+      Passes.add(createBitcodeWriterPass(*OS, PreserveBitcodeUseListOrder));
   }
 
   // Before executing passes, print the final values of the LLVM options.
@@ -598,6 +615,27 @@ int main(int argc, char **argv) {
   // Now that we have all of the passes ready, run them.
   Passes.run(*M);
 
+  // If requested, run all passes again with the same pass manager to catch
+  // bugs caused by persistent state in the passes
+  if (RunTwice) {
+    CompileTwiceBuffer = Buffer;
+    Buffer.clear();
+    std::unique_ptr<Module> M2(CloneModule(M.get()));
+    Passes.run(*M2);
+    if (Buffer.size() != CompileTwiceBuffer.size() ||
+        (memcmp(Buffer.data(), CompileTwiceBuffer.data(), Buffer.size()) !=
+         0)) {
+      errs() << "Running the pass manager twice changed the output.\n"
+                "Writing the result of the second run to the specified output."
+                "To generate the one-run comparison binary, just run without\n"
+                "the compile-twice option\n";
+      Out->os() << BOS->str();
+      Out->keep();
+      return 1;
+    }
+    Out->os() << BOS->str();
+  }
+
   // Declare success.
   if (!NoOutput || PrintBreakpoints)
     Out->keep();
-- 
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