Add some switches helpful for debugging:

-print-before=<Pass Name>

Dump IR before running pass <Pass Name>.

-print-before-all

Dump IR before running each pass.

-print-after-all

Dump IR after running each pass.

These are helpful when tracking down a miscompilation.  It is easy to
get IR dumps and do diffs on them, etc.

To make this work well, add a new getPrinterPass API to Pass so that
each kind of pass (ModulePass, FunctionPass, etc.) can create a Pass
suitable for dumping out the kind of object the Pass works on.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@100143 91177308-0d34-0410-b5e6-96231b3b80d8

lib/VMCore/PrintModulePass.cpp

@@ -23,21 +23,22 @@ using namespace llvm;
 namespace {
 
   class PrintModulePass : public ModulePass {
+    std::string Banner;
     raw_ostream *Out;       // raw_ostream to print on
     bool DeleteStream;      // Delete the ostream in our dtor?
   public:
     static char ID;
     PrintModulePass() : ModulePass(&ID), Out(&dbgs()), 
       DeleteStream(false) {}
-    PrintModulePass(raw_ostream *o, bool DS)
-      : ModulePass(&ID), Out(o), DeleteStream(DS) {}
+    PrintModulePass(const std::string &B, raw_ostream *o, bool DS)
+        : ModulePass(&ID), Banner(B), Out(o), DeleteStream(DS) {}
     
     ~PrintModulePass() {
       if (DeleteStream) delete Out;
     }
     
     bool runOnModule(Module &M) {
-      (*Out) << M;
+      (*Out) << Banner << M;
       return false;
     }
     
@@ -85,8 +86,9 @@ Y("print-function","Print function to stderr");
 /// createPrintModulePass - Create and return a pass that writes the
 /// module to the specified raw_ostream.
 ModulePass *llvm::createPrintModulePass(llvm::raw_ostream *OS, 
-                                        bool DeleteStream) {
-  return new PrintModulePass(OS, DeleteStream);
+                                        bool DeleteStream,
+                                        const std::string &Banner) {
+  return new PrintModulePass(Banner, OS, DeleteStream);
 }
 
 /// createPrintFunctionPass - Create and return a pass that prints