Replace all weight-based interfaces in MBB with probability-based interfaces, and update all uses of old interfaces.

The patch in http://reviews.llvm.org/D13745 is broken into four parts:

1. New interfaces without functional changes (http://reviews.llvm.org/D13908).
2. Use new interfaces in SelectionDAG, while in other passes treat probabilities
as weights (http://reviews.llvm.org/D14361).
3. Use new interfaces in all other passes.
4. Remove old interfaces.

This patch is 3+4 above. In this patch, MBB won't provide weight-based
interfaces any more, which are totally replaced by probability-based ones.
The interface addSuccessor() is redesigned so that the default probability is
unknown. We allow unknown probabilities but don't allow using it together
with known probabilities in successor list. That is to say, we either have a
list of successors with all known probabilities, or all unknown
probabilities. In the latter case, we assume each successor has 1/N
probability where N is the number of successors. An assertion checks if the
user is attempting to add a successor with the disallowed mixed use as stated
above. This can help us catch many misuses.

All uses of weight-based interfaces are now updated to use probability-based
ones.


Differential revision: http://reviews.llvm.org/D14973

llvm-svn: 254348

1 files changed, 18 insertions, 2 deletions

diff --git a/llvm/lib/Support/BranchProbability.cpp b/llvm/lib/Support/BranchProbability.cpp
index 3b0f6e6..771d02c 100644
--- a/llvm/lib/Support/BranchProbability.cpp
+++ b/llvm/lib/Support/BranchProbability.cpp
@@ -22,11 +22,14 @@ using namespace llvm;
 const uint32_t BranchProbability::D;
 
 raw_ostream &BranchProbability::print(raw_ostream &OS) const {
+  if (isUnknown())
+    return OS << "?%";
+
   // Get a percentage rounded to two decimal digits. This avoids
   // implementation-defined rounding inside printf.
   double Percent = rint(((double)N / D) * 100.0 * 100.0) / 100.0;
-  OS << format("0x%08" PRIx32 " / 0x%08" PRIx32 " = %.2f%%", N, D, Percent);
-  return OS;
+  return OS << format("0x%08" PRIx32 " / 0x%08" PRIx32 " = %.2f%%", N, D,
+                      Percent);
 }
 
 void BranchProbability::dump() const { print(dbgs()) << '\n'; }
@@ -43,6 +46,19 @@ BranchProbability::BranchProbability(uint32_t Numerator, uint32_t Denominator) {
   }
 }
 
+BranchProbability
+BranchProbability::getBranchProbability(uint64_t Numerator,
+                                        uint64_t Denominator) {
+  assert(Numerator <= Denominator && "Probability cannot be bigger than 1!");
+  // Scale down Denominator to fit in a 32-bit integer.
+  int Scale = 0;
+  while (Denominator > UINT32_MAX) {
+    Denominator >>= 1;
+    Scale++;
+  }
+  return BranchProbability(Numerator >> Scale, Denominator);
+}
+
 // If ConstD is not zero, then replace D by ConstD so that division and modulo
 // operations by D can be optimized, in case this function is not inlined by the
 // compiler.