[PATCH] D40891: Revert a change in propagateMassToSuccessors that summed redundant edges n^2 times

[Andrew Scheidecker via Phabricator via llvm-commits]

AndrewScheidecker updated this revision to Diff 126063.
AndrewScheidecker retitled this revision from "Fix accidentally quadratic time in BlockFrequencyInfoImpl::propagateMassToSuccessors" to "Revert a change in propagateMassToSuccessors that summed redundant edges n^2 times".
AndrewScheidecker edited the summary of this revision.
AndrewScheidecker added a comment.

Added a test that produces different results with and without this fix


Repository:
  rL LLVM

https://reviews.llvm.org/D40891

Files:
  include/llvm/Analysis/BlockFrequencyInfoImpl.h
  test/Analysis/BlockFrequencyInfo/redundant_edges.ll


Index: test/Analysis/BlockFrequencyInfo/redundant_edges.ll
===================================================================
--- /dev/null
+++ test/Analysis/BlockFrequencyInfo/redundant_edges.ll
@@ -0,0 +1,35 @@
+; RUN: opt < %s -analyze -block-freq | FileCheck %s
+; RUN: opt < %s -analyze -lazy-block-freq | FileCheck %s
+; RUN: opt < %s -passes='print<block-freq>' -disable-output 2>&1 | FileCheck %s
+
+define i32 @test1(i32) {
+; CHECK-LABEL: Printing analysis {{.*}} for function 'test1':
+; CHECK-NEXT: block-frequency-info: test1
+; CHECK-NEXT: entry: float = 1.0, int = [[ENTRY:[0-9]+]]
+entry:
+  br label %loop
+
+; CHECK-NEXT: loop: float = 32.0
+loop:
+  %i = phi i32 [%0, %entry], [%i.next, %blockEnd]
+  switch i32 %i, label %blockEnd [
+    i32 0, label %return
+    i32 1, label %return
+    i32 2, label %return
+    i32 3, label %return
+    i32 4, label %return
+    i32 5, label %return
+    i32 6, label %return
+    i32 7, label %return
+  ]
+
+; CHECK-NEXT: blockEnd: float = 31.0
+blockEnd:
+  %i.next = add i32 %i, 1
+  br label %loop
+
+; CHECK-NEXT: return: float = 1.0
+return:
+  %ret = phi i32 [ 0, %loop ], [ 0, %loop ], [ 0, %loop ], [ 0, %loop ], [ 0, %loop ], [ 0, %loop ], [ 0, %loop ], [ 0, %loop ]
+  ret i32 %ret
+}
Index: include/llvm/Analysis/BlockFrequencyInfoImpl.h
===================================================================
--- include/llvm/Analysis/BlockFrequencyInfoImpl.h
+++ include/llvm/Analysis/BlockFrequencyInfoImpl.h
@@ -1315,9 +1315,12 @@
       return false;
   } else {
     const BlockT *BB = getBlock(Node);
-    for (const auto Succ : children<const BlockT *>(BB))
-      if (!addToDist(Dist, OuterLoop, Node, getNode(Succ),
-                     getWeightFromBranchProb(BPI->getEdgeProbability(BB, Succ))))
+    for (auto SuccI = GraphTraits<const BlockT *>::child_begin(BB),
+              SuccE = GraphTraits<const BlockT *>::child_end(BB);
+         SuccI != SuccE; ++SuccI)
+      if (!addToDist(
+              Dist, OuterLoop, Node, getNode(*SuccI),
+              getWeightFromBranchProb(BPI->getEdgeProbability(BB, SuccI))))
         // Irreducible backedge.
         return false;
   }


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