Record whether the weights on out-edges from a MBB are normalized.

1. Create a utility function normalizeEdgeWeights() in MachineBranchProbabilityInfo that normalizes a list of edge weights so that the sum of then can fit in uint32_t.
2. Provide an interface in MachineBasicBlock to normalize its successors' weights.
3. Add a flag in MachineBasicBlock that tracks whether its successors' weights are normalized.
4. Provide an overload of getSumForBlock that accepts a non-const pointer to a MBB so that it can force normalizing this MBB's successors' weights.
5. Update several uses of getSumForBlock() by eliminating the once needed weight scale.

Differential Revision: http://reviews.llvm.org/D11442

llvm-svn: 244154

1 files changed, 26 insertions, 4 deletions

diff --git a/llvm/lib/CodeGen/MachineBasicBlock.cpp b/llvm/lib/CodeGen/MachineBasicBlock.cpp
index 5d3f7eb..e2f381e 100644
--- a/llvm/lib/CodeGen/MachineBasicBlock.cpp
+++ b/llvm/lib/CodeGen/MachineBasicBlock.cpp
@@ -16,6 +16,7 @@
 #include "llvm/ADT/SmallString.h"
 #include "llvm/CodeGen/LiveIntervalAnalysis.h"
 #include "llvm/CodeGen/LiveVariables.h"
+#include "llvm/CodeGen/MachineBranchProbabilityInfo.h"
 #include "llvm/CodeGen/MachineDominators.h"
 #include "llvm/CodeGen/MachineFunction.h"
 #include "llvm/CodeGen/MachineInstrBuilder.h"
@@ -39,8 +40,9 @@ using namespace llvm;
 #define DEBUG_TYPE "codegen"
 
 MachineBasicBlock::MachineBasicBlock(MachineFunction &mf, const BasicBlock *bb)
-  : BB(bb), Number(-1), xParent(&mf), Alignment(0), IsLandingPad(false),
-    AddressTaken(false), CachedMCSymbol(nullptr) {
+    : BB(bb), Number(-1), AreSuccWeightsNormalized(false), xParent(&mf),
+      Alignment(0), IsLandingPad(false), AddressTaken(false),
+      CachedMCSymbol(nullptr) {
   Insts.Parent = this;
 }
 
@@ -481,8 +483,10 @@ void MachineBasicBlock::addSuccessor(MachineBasicBlock *succ, uint32_t weight) {
   if (weight != 0 && Weights.empty())
     Weights.resize(Successors.size());
 
-  if (weight != 0 || !Weights.empty())
+  if (weight != 0 || !Weights.empty()) {
     Weights.push_back(weight);
+    AreSuccWeightsNormalized = false;
+  }
 
    Successors.push_back(succ);
    succ->addPredecessor(this);
@@ -1096,7 +1100,25 @@ uint32_t MachineBasicBlock::getSuccWeight(const_succ_iterator Succ) const {
 void MachineBasicBlock::setSuccWeight(succ_iterator I, uint32_t weight) {
   if (Weights.empty())
     return;
-  *getWeightIterator(I) = weight;
+  auto WeightIter = getWeightIterator(I);
+  uint32_t OldWeight = *WeightIter;
+  *WeightIter = weight;
+  if (weight > OldWeight)
+    AreSuccWeightsNormalized = false;
+}
+
+/// Normalize all succesor weights so that the sum of them does not exceed
+/// UINT32_MAX. Return true if the weights are modified and false otherwise.
+/// Note that weights that are modified after calling this function are not
+/// guaranteed to be normalized.
+bool MachineBasicBlock::normalizeSuccWeights() {
+  if (!AreSuccWeightsNormalized) {
+    uint32_t Scale =
+        MachineBranchProbabilityInfo::normalizeEdgeWeights(Weights);
+    AreSuccWeightsNormalized = true;
+    return Scale != 1;
+  }
+  return false;
 }
 
 /// getWeightIterator - Return wight iterator corresonding to the I successor