PGO: preserve branch-weight metadata when simplifying Switch

Hanlde the case when we split the default edge if the default target has "icmp"
and unconditinal branch.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@164076 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 51 insertions, 1 deletions

diff --git a/lib/Transforms/Utils/SimplifyCFG.cpp b/lib/Transforms/Utils/SimplifyCFG.cpp
index 67cb8f5..1316b85 100644
--- a/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -2425,6 +2425,21 @@ static bool TryToSimplifyUncondBranchWithICmpInIt(ICmpInst *ICI,
   // the switch to the merge point on the compared value.
   BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), "switch.edge",
                                          BB->getParent(), BB);
+  SmallVector<uint64_t, 8> Weights;
+  bool HasWeights = HasBranchWeights(SI);
+  if (HasWeights) {
+    GetBranchWeights(SI, Weights);
+    if (Weights.size() == 1 + SI->getNumCases()) {
+      // Split weight for default case to case for "Cst".
+      Weights[0] = (Weights[0]+1) >> 1;
+      Weights.push_back(Weights[0]);
+
+      SmallVector<uint32_t, 8> MDWeights(Weights.begin(), Weights.end());
+      SI->setMetadata(LLVMContext::MD_prof,
+                      MDBuilder(SI->getContext()).
+                      createBranchWeights(MDWeights));
+    }
+  }
   SI->addCase(Cst, NewBB);
 
   // NewBB branches to the phi block, add the uncond branch and the phi entry.
diff --git a/test/Transforms/SimplifyCFG/preserve-branchweights.ll b/test/Transforms/SimplifyCFG/preserve-branchweights.ll
index 2347cb6..4b78747 100644
--- a/test/Transforms/SimplifyCFG/preserve-branchweights.ll
+++ b/test/Transforms/SimplifyCFG/preserve-branchweights.ll
@@ -216,6 +216,40 @@ bees:
     ret void
 }
 
+; Test edge splitting when the default target has icmp and unconditinal
+; branch
+define i1 @test9(i32 %x, i32 %y) nounwind {
+; CHECK: @test9
+entry:
+    switch i32 %x, label %bees [
+        i32 0, label %a
+        i32 1, label %end
+        i32 2, label %end
+    ], !prof !7
+; CHECK: switch i32 %x, label %bees [
+; CHECK: i32 0, label %a
+; CHECK: i32 1, label %end
+; CHECK: i32 2, label %end
+; CHECK: i32 92, label %end
+; CHECK: ], !prof !7
+
+a:
+    call void @helper(i32 0) nounwind
+    %reta = icmp slt i32 %x, %y
+    ret i1 %reta
+
+bees:
+    %tmp = icmp eq i32 %x, 92
+    br label %end
+
+end:
+; CHECK: end:
+; CHECK: %ret = phi i1 [ true, %entry ], [ false, %bees ], [ true, %entry ], [ true, %entry ]
+    %ret = phi i1 [ true, %entry ], [%tmp, %bees], [true, %entry]
+    call void @helper(i32 2) nounwind
+    ret i1 %ret
+}
+
 !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}
@@ -232,4 +266,5 @@ bees:
 ; CHECK: !4 = metadata !{metadata !"branch_weights", i32 11, i32 5}
 ; CHECK: !5 = metadata !{metadata !"branch_weights", i32 17, i32 15} 
 ; CHECK: !6 = metadata !{metadata !"branch_weights", i32 9, i32 7}
-; CHECK-NOT: !7
+; CHECK: !7 = metadata !{metadata !"branch_weights", i32 17, i32 9, i32 8, i32 7, i32 17}
+; CHECK-NOT: !8