[llvm] r250240 - Update MachineBranchProbabilityInfo::normalizeEdgeWeights to make sure there is no zero weight in the output, and also add a missing test for JumpThreading.

[Cong Hou via llvm-commits]

Author: conghou
Date: Tue Oct 13 17:27:41 2015
New Revision: 250240

URL: http://llvm.org/viewvc/llvm-project?rev=250240&view=rev
Log:
Update MachineBranchProbabilityInfo::normalizeEdgeWeights to make sure there is no zero weight in the output, and also add a missing test for JumpThreading.

The test is for the patch in http://reviews.llvm.org/D10979 but was missing when committing that patch.


Added:
    llvm/trunk/test/Transforms/JumpThreading/update-edge-weight.ll
Modified:
    llvm/trunk/include/llvm/CodeGen/MachineBranchProbabilityInfo.h

Modified: llvm/trunk/include/llvm/CodeGen/MachineBranchProbabilityInfo.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/CodeGen/MachineBranchProbabilityInfo.h?rev=250240&r1=250239&r2=250240&view=diff
==============================================================================
--- llvm/trunk/include/llvm/CodeGen/MachineBranchProbabilityInfo.h (original)
+++ llvm/trunk/include/llvm/CodeGen/MachineBranchProbabilityInfo.h Tue Oct 13 17:27:41 2015
@@ -86,35 +86,43 @@ public:
                                     const MachineBasicBlock *Dst) const;
 
   // Normalize a list of weights by scaling them down so that the sum of them
-  // doesn't exceed UINT32_MAX. Return the scale.
+  // doesn't exceed UINT32_MAX.
   template <class WeightListIter>
-  static uint32_t normalizeEdgeWeights(WeightListIter Begin,
-                                       WeightListIter End);
+  static void normalizeEdgeWeights(WeightListIter Begin, WeightListIter End);
 };
 
 template <class WeightListIter>
-uint32_t
-MachineBranchProbabilityInfo::normalizeEdgeWeights(WeightListIter Begin,
-                                                   WeightListIter End) {
+void MachineBranchProbabilityInfo::normalizeEdgeWeights(WeightListIter Begin,
+                                                        WeightListIter End) {
   // First we compute the sum with 64-bits of precision.
   uint64_t Sum = std::accumulate(Begin, End, uint64_t(0));
 
-  // If Sum is zero, set all weights to 1.
-  if (Sum == 0)
-    std::fill(Begin, End, uint64_t(1));
-
-  // If the computed sum fits in 32-bits, we're done.
-  if (Sum <= UINT32_MAX)
-    return 1;
-
-  // Otherwise, compute the scale necessary to cause the weights to fit, and
-  // re-sum with that scale applied.
-  assert((Sum / UINT32_MAX) < UINT32_MAX &&
-         "The sum of weights exceeds UINT32_MAX^2!");
-  uint32_t Scale = (Sum / UINT32_MAX) + 1;
-  for (auto I = Begin; I != End; ++I)
-    *I /= Scale;
-  return Scale;
+  if (Sum > UINT32_MAX) {
+    // Compute the scale necessary to cause the weights to fit, and re-sum with
+    // that scale applied.
+    assert(Sum / UINT32_MAX < UINT32_MAX &&
+           "The sum of weights exceeds UINT32_MAX^2!");
+    uint32_t Scale = Sum / UINT32_MAX + 1;
+    for (auto I = Begin; I != End; ++I)
+      *I /= Scale;
+    Sum = std::accumulate(Begin, End, uint64_t(0));
+  }
+
+  // Eliminate zero weights.
+  auto ZeroWeightNum = std::count(Begin, End, 0u);
+  if (ZeroWeightNum > 0) {
+    // If all weights are zeros, replace them by 1.
+    if (Sum == 0)
+      std::fill(Begin, End, 1u);
+    else {
+      // Scale up non-zero weights and turn zero weights into ones.
+      uint64_t ScalingFactor = (UINT32_MAX - ZeroWeightNum) / Sum;
+      if (ScalingFactor > 1)
+        for (auto I = Begin; I != End; ++I)
+          *I *= ScalingFactor;
+      std::replace(Begin, End, 0u, 1u);
+    }
+  }
 }
 
 }

Added: llvm/trunk/test/Transforms/JumpThreading/update-edge-weight.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/JumpThreading/update-edge-weight.ll?rev=250240&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/JumpThreading/update-edge-weight.ll (added)
+++ llvm/trunk/test/Transforms/JumpThreading/update-edge-weight.ll Tue Oct 13 17:27:41 2015
@@ -0,0 +1,43 @@
+; RUN: opt -S -jump-threading %s | FileCheck %s
+
+; Test if edge weights are properly updated after jump threading.
+
+; CHECK: !2 = !{!"branch_weights", i32 22, i32 7}
+
+define void @foo(i32 %n) !prof !0 {
+entry:
+  %cmp = icmp sgt i32 %n, 10
+  br i1 %cmp, label %if.then.1, label %if.else.1, !prof !1
+
+if.then.1:
+  tail call void @a()
+  br label %if.cond
+
+if.else.1:
+  tail call void @b()
+  br label %if.cond
+
+if.cond:
+  %cmp1 = icmp sgt i32 %n, 5
+  br i1 %cmp1, label %if.then.2, label %if.else.2, !prof !2
+
+if.then.2:
+  tail call void @c()
+  br label %if.end
+
+if.else.2:
+  tail call void @d()
+  br label %if.end
+
+if.end:
+  ret void
+}
+
+declare void @a()
+declare void @b()
+declare void @c()
+declare void @d()
+
+!0 = !{!"function_entry_count", i64 1}
+!1 = !{!"branch_weights", i32 10, i32 5}
+!2 = !{!"branch_weights", i32 10, i32 1}