[GlobalISel] Reporting rules covered as part of the InstructionSelect's debug-only printing

[rtereshin]

Summary

The main goal of this change is to make it much easier to track which rules are actually covered by Testgen'erated regression tests.

Originally part of the larger https://reviews.llvm.org/D43962 ([GlobalISel][utils] Adding the init version of Instruction Select Testgen) patch, extracted as to make it smaller and more targeted.

Partially reviewed by @dsanders within the patch mentioned.

[rtereshin]

@aemerson Thanks!

llvm/trunk/include/llvm/Support/CodeGenCoverage.h

 class LLVMContext;
 class MemoryBuffer;
 
 class CodeGenCoverage {
 protected:
   BitVector RuleCoverage;
 
 public:
+  using const_covered_iterator = BitVector::const_set_bits_iterator;
+
   CodeGenCoverage();
 
   void setCovered(uint64_t RuleID);
-  bool isCovered(uint64_t RuleID);
+  bool isCovered(uint64_t RuleID) const;
+  iterator_range<const_covered_iterator> covered() const;
 
   bool parse(MemoryBuffer &Buffer, StringRef BackendName);
   bool emit(StringRef FilePrefix, StringRef BackendName) const;
   void reset();
 };
-} // end namespace llvm
+} // namespace llvm
 
 #endif // ifndef LLVM_SUPPORT_CODEGENCOVERAGE_H

llvm/trunk/lib/CodeGen/GlobalISel/InstructionSelect.cpp

if (MF.size() != NumBlocks) {
     R << "inserting blocks is not supported yet";
     reportGISelFailure(MF, TPC, MORE, R);
     return false;
   }
 
   auto &TLI = *MF.getSubtarget().getTargetLowering();
   TLI.finalizeLowering(MF);
 
+  DEBUG({
+    dbgs() << "Rules covered by selecting function: " << MF.getName() << ":";
+    for (auto RuleID : CoverageInfo.covered())
+      dbgs() << " id" << RuleID;
+    dbgs() << "\n\n";
+  });
   CoverageInfo.emit(CoveragePrefix,
                     MF.getSubtarget()
                         .getTargetLowering()
                         ->getTargetMachine()
                         .getTarget()
                         .getBackendName());
 
   // If we successfully selected the function nothing is going to use the vreg
   // types after us (otherwise MIRPrinter would need them). Make sure the types
   // disappear.
   MRI.getVRegToType().clear();
 
   // FIXME: Should we accurately track changes?
   return true;
 }

llvm/trunk/lib/Support/CodeGenCoverage.cpp

 CodeGenCoverage::CodeGenCoverage() {}
 
 void CodeGenCoverage::setCovered(uint64_t RuleID) {
   if (RuleCoverage.size() <= RuleID)
     RuleCoverage.resize(RuleID + 1, 0);
   RuleCoverage[RuleID] = true;
 }
 
-bool CodeGenCoverage::isCovered(uint64_t RuleID) {
+bool CodeGenCoverage::isCovered(uint64_t RuleID) const {
   if (RuleCoverage.size() <= RuleID)
     return false;
   return RuleCoverage[RuleID];
 }
 
+iterator_range<CodeGenCoverage::const_covered_iterator>
+CodeGenCoverage::covered() const {
+  return RuleCoverage.set_bits();
+}
+
 bool CodeGenCoverage::parse(MemoryBuffer &Buffer, StringRef BackendName) {
   const char *CurPtr = Buffer.getBufferStart();
 
   while (CurPtr != Buffer.getBufferEnd()) {
     // Read the backend name from the input.
     const char *LexedBackendName = CurPtr;
     while (*CurPtr++ != 0)
       ;