PGO: preserve branch-weight metadata when simplifying two branches with a common

destination in SimplifyCondBranchToCondBranch.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@164054 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/Utils/SimplifyCFG.cpp b/lib/Transforms/Utils/SimplifyCFG.cpp
index 091d63d67db583a201241e8fd479d4f98d1e8f89..5a8d2e46899a3cafdfc70d8cfb47c26af01e139a 100644 (file)
--- a/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -2150,6 +2150,33 @@ static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI) {
   PBI->setSuccessor(0, CommonDest);
   PBI->setSuccessor(1, OtherDest);
 
+  // Update branch weight for PBI.
+  uint64_t PredTrueWeight, PredFalseWeight, SuccTrueWeight, SuccFalseWeight;
+  bool PredHasWeights = ExtractBranchMetadata(PBI, PredTrueWeight,
+                                              PredFalseWeight);
+  bool SuccHasWeights = ExtractBranchMetadata(BI, SuccTrueWeight,
+                                              SuccFalseWeight);
+  if (PredHasWeights && SuccHasWeights) {
+    uint64_t PredCommon = PBIOp ? PredFalseWeight : PredTrueWeight;
+    uint64_t PredOther = PBIOp ?PredTrueWeight : PredFalseWeight;
+    uint64_t SuccCommon = BIOp ? SuccFalseWeight : SuccTrueWeight;
+    uint64_t SuccOther = BIOp ? SuccTrueWeight : SuccFalseWeight;
+    // The weight to CommonDest should be PredCommon * SuccTotal +
+    //                                    PredOther * SuccCommon.
+    // The weight to OtherDest should be PredOther * SuccOther.
+    SmallVector<uint64_t, 2> NewWeights;
+    NewWeights.push_back(PredCommon * (SuccCommon + SuccOther) +
+                         PredOther * SuccCommon);
+    NewWeights.push_back(PredOther * SuccOther);
+    // Halve the weights if any of them cannot fit in an uint32_t
+    FitWeights(NewWeights);
+
+    SmallVector<uint32_t, 2> MDWeights(NewWeights.begin(),NewWeights.end());
+    PBI->setMetadata(LLVMContext::MD_prof,
+                     MDBuilder(BI->getContext()).
+                     createBranchWeights(MDWeights));
+  }
+
   // OtherDest may have phi nodes.  If so, add an entry from PBI's
   // block that are identical to the entries for BI's block.
   AddPredecessorToBlock(OtherDest, PBI->getParent(), BB);

diff --git a/test/Transforms/SimplifyCFG/preserve-branchweights.ll b/test/Transforms/SimplifyCFG/preserve-branchweights.ll
index 1564e4e11d7e498ebd2051ee9a86ea4a2671ca80..98a47e8e0c8a78bd24843740c9795855eac8f723 100644 (file)
--- a/test/Transforms/SimplifyCFG/preserve-branchweights.ll
+++ b/test/Transforms/SimplifyCFG/preserve-branchweights.ll
@@ -174,16 +174,37 @@ Z:
   ret void
 }
 
+define void @test7(i1 %a, i1 %b) {
+; CHECK: @test7
+entry:
+  %c = or i1 %b, false
+  br i1 %a, label %Y, label %X, !prof !0
+; CHECK: br i1 %brmerge, label %Y, label %Z, !prof !5
+
+X:
+  br i1 %c, label %Y, label %Z, !prof !6
+
+Y:
+  call void @helper(i32 0)
+  ret void
+
+Z:
+  call void @helper(i32 1)
+  ret void
+}
+
 !0 = metadata !{metadata !"branch_weights", i32 3, i32 5}
 !1 = metadata !{metadata !"branch_weights", i32 1, i32 1}
 !2 = metadata !{metadata !"branch_weights", i32 1, i32 2}
 !3 = metadata !{metadata !"branch_weights", i32 4, i32 3, i32 2, i32 1}
 !4 = metadata !{metadata !"branch_weights", i32 4, i32 3, i32 2, i32 1}
 !5 = metadata !{metadata !"branch_weights", i32 7, i32 6, i32 5}
+!6 = metadata !{metadata !"branch_weights", i32 1, i32 3}
 
 ; CHECK: !0 = metadata !{metadata !"branch_weights", i32 5, i32 11}
 ; CHECK: !1 = metadata !{metadata !"branch_weights", i32 1, i32 5}
 ; CHECK: !2 = metadata !{metadata !"branch_weights", i32 7, i32 1, i32 2}
 ; CHECK: !3 = metadata !{metadata !"branch_weights", i32 49, i32 12, i32 24, i32 35}
 ; CHECK: !4 = metadata !{metadata !"branch_weights", i32 11, i32 5}
-; CHECK-NOT: !5
+; CHECK: !5 = metadata !{metadata !"branch_weights", i32 17, i32 15} 
+; CHECK-NOT: !6