[Debugify] Export per-pass debug info loss statistics

Add a -debugify-export option to opt. This exports per-pass `debugify`
loss statistics to a file in CSV format.

For some interesting numbers on debug value loss during an -O2 build
of the sqlite3 amalgamation, see the review thread.

Differential Revision: https://reviews.llvm.org/D49003

llvm-svn: 337787

1 files changed, 21 insertions, 2 deletions

diff --git a/llvm/tools/opt/opt.cpp b/llvm/tools/opt/opt.cpp
index 98ad700409c..6e287b6c0ab 100644
--- a/llvm/tools/opt/opt.cpp
+++ b/llvm/tools/opt/opt.cpp
@@ -217,6 +217,11 @@ static cl::opt<bool> DebugifyEach(
     cl::desc(
         "Start each pass with debugify and end it with check-debugify"));
 
+static cl::opt<std::string>
+    DebugifyExport("debugify-export",
+                   cl::desc("Export per-pass debugify statistics to this file"),
+                   cl::value_desc("filename"), cl::init(""));
+
 static cl::opt<bool>
 PrintBreakpoints("print-breakpoints-for-testing",
                  cl::desc("Print select breakpoints location for testing"));
@@ -267,34 +272,45 @@ static cl::opt<std::string>
                     cl::value_desc("filename"));
 
 class OptCustomPassManager : public legacy::PassManager {
+  DebugifyStatsMap DIStatsMap;
+
 public:
   using super = legacy::PassManager;
 
   void add(Pass *P) override {
+    // Wrap each pass with (-check)-debugify passes if requested, making
+    // exceptions for passes which shouldn't see -debugify instrumentation.
     bool WrapWithDebugify = DebugifyEach && !P->getAsImmutablePass() &&
                             !isIRPrintingPass(P) && !isBitcodeWriterPass(P);
     if (!WrapWithDebugify) {
       super::add(P);
       return;
     }
+
+    // Apply -debugify/-check-debugify before/after each pass and collect
+    // debug info loss statistics.
     PassKind Kind = P->getPassKind();
+    StringRef Name = P->getPassName();
+
     // TODO: Implement Debugify for BasicBlockPass, LoopPass.
     switch (Kind) {
       case PT_Function:
         super::add(createDebugifyFunctionPass());
         super::add(P);
-        super::add(createCheckDebugifyFunctionPass(true, P->getPassName()));
+        super::add(createCheckDebugifyFunctionPass(true, Name, &DIStatsMap));
         break;
       case PT_Module:
         super::add(createDebugifyModulePass());
         super::add(P);
-        super::add(createCheckDebugifyModulePass(true, P->getPassName()));
+        super::add(createCheckDebugifyModulePass(true, Name, &DIStatsMap));
         break;
       default:
         super::add(P);
         break;
     }
   }
+
+  const DebugifyStatsMap &getDebugifyStatsMap() const { return DIStatsMap; }
 };
 
 static inline void addPass(legacy::PassManagerBase &PM, Pass *P) {
@@ -839,6 +855,9 @@ int main(int argc, char **argv) {
     Out->os() << BOS->str();
   }
 
+  if (DebugifyEach && !DebugifyExport.empty())
+    exportDebugifyStats(DebugifyExport, Passes.getDebugifyStatsMap());
+
   // Declare success.
   if (!NoOutput || PrintBreakpoints)
     Out->keep();