Introduce DebugCounter into ConstProp pass

Summary:
This patch introduces DebugCounter into ConstProp pass at per-transformation level.

It will provide an option to skip first n or stop after n transformations for the whole ConstProp pass.

This will make debug easier for the pass, also providing chance to do transformation level bisecting.

Reviewers: davide, fhahn

Reviewed By: fhahn

Subscribers: llozano, george.burgess.iv, llvm-commits

Differential Revision: https://reviews.llvm.org/D50094

llvm-svn: 346720

llvm/lib/Transforms/Scalar/ConstantProp.cpp

@@ -18,21 +18,25 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/Statistic.h"
 #include "llvm/Analysis/ConstantFolding.h"
 #include "llvm/Analysis/TargetLibraryInfo.h"
-#include "llvm/Transforms/Utils/Local.h"
 #include "llvm/IR/Constant.h"
 #include "llvm/IR/InstIterator.h"
 #include "llvm/IR/Instruction.h"
 #include "llvm/Pass.h"
+#include "llvm/Support/DebugCounter.h"
 #include "llvm/Transforms/Scalar.h"
-#include <set>
+#include "llvm/Transforms/Utils/Local.h"
 using namespace llvm;
 
 #define DEBUG_TYPE "constprop"
 
 STATISTIC(NumInstKilled, "Number of instructions killed");
+DEBUG_COUNTER(CPCounter, "constprop-transform",
+              "Controls which instructions are killed");
 
 namespace {
   struct ConstantPropagation : public FunctionPass {
@@ -66,9 +70,15 @@ bool ConstantPropagation::runOnFunction(Function &F) {
     return false;
 
   // Initialize the worklist to all of the instructions ready to process...
-  std::set<Instruction*> WorkList;
-  for (Instruction &I: instructions(&F))
+  SmallPtrSet<Instruction *, 16> WorkList;
+  // The SmallVector of WorkList ensures that we do iteration at stable order.
+  // We use two containers rather than one SetVector, since remove is
+  // linear-time, and we don't care enough to remove from Vec.
+  SmallVector<Instruction *, 16> WorkListVec;
+  for (Instruction &I : instructions(&F)) {
     WorkList.insert(&I);
+    WorkListVec.push_back(&I);
+  }
 
   bool Changed = false;
   const DataLayout &DL = F.getParent()->getDataLayout();
@@ -76,29 +86,36 @@ bool ConstantPropagation::runOnFunction(Function &F) {
       &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
 
   while (!WorkList.empty()) {
-    Instruction *I = *WorkList.begin();
-    WorkList.erase(WorkList.begin());    // Get an element from the worklist...
+    SmallVector<Instruction*, 16> NewWorkListVec;
+    for (auto *I : WorkListVec) {
+      WorkList.erase(I); // Remove element from the worklist...
 
-    if (!I->use_empty())                 // Don't muck with dead instructions...
-      if (Constant *C = ConstantFoldInstruction(I, DL, TLI)) {
-        // Add all of the users of this instruction to the worklist, they might
-        // be constant propagatable now...
-        for (User *U : I->users())
-          WorkList.insert(cast<Instruction>(U));
+      if (!I->use_empty()) // Don't muck with dead instructions...
+        if (Constant *C = ConstantFoldInstruction(I, DL, TLI)) {
+          if (!DebugCounter::shouldExecute(CPCounter))
+            continue;
 
-        // Replace all of the uses of a variable with uses of the constant.
-        I->replaceAllUsesWith(C);
+          // Add all of the users of this instruction to the worklist, they might
+          // be constant propagatable now...
+          for (User *U : I->users()) {
+            // If user not in the set, then add it to the vector.
+            if (WorkList.insert(cast<Instruction>(U)).second)
+              NewWorkListVec.push_back(cast<Instruction>(U));
+          }
 
-        // Remove the dead instruction.
-        WorkList.erase(I);
-        if (isInstructionTriviallyDead(I, TLI)) {
-          I->eraseFromParent();
-          ++NumInstKilled;
+          // Replace all of the uses of a variable with uses of the constant.
+          I->replaceAllUsesWith(C);
+
+          if (isInstructionTriviallyDead(I, TLI)) {
+            I->eraseFromParent();
+            ++NumInstKilled;
+          }
+
+          // We made a change to the function...
+          Changed = true;
         }
-
-        // We made a change to the function...
-        Changed = true;
-      }
+    }
+    WorkListVec = std::move(NewWorkListVec);
   }
   return Changed;
 }