PGO: preserve branch-weight metadata when removing a case which jumps

to the default target.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@163724 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/Utils/Local.cpp b/lib/Transforms/Utils/Local.cpp
index 060143356534aedb3341956d4cf51d600d29ba7f..dc6b506a3bac75fcdeeb95480c4e90f0ebf56ccf 100644 (file)
--- a/lib/Transforms/Utils/Local.cpp
+++ b/lib/Transforms/Utils/Local.cpp
@@ -23,6 +23,7 @@
 #include "llvm/Instructions.h"
 #include "llvm/IntrinsicInst.h"
 #include "llvm/Intrinsics.h"
+#include "llvm/MDBuilder.h"
 #include "llvm/Metadata.h"
 #include "llvm/Operator.h"
 #include "llvm/ADT/DenseMap.h"
@@ -122,6 +123,27 @@ bool llvm::ConstantFoldTerminator(BasicBlock *BB, bool DeleteDeadConditions,
       // Check to see if this branch is going to the same place as the default
       // dest.  If so, eliminate it as an explicit compare.
       if (i.getCaseSuccessor() == DefaultDest) {
+        MDNode* MD = SI->getMetadata(LLVMContext::MD_prof);
+        // MD should have 2 + NumCases operands.
+        if (MD && MD->getNumOperands() == 2 + SI->getNumCases()) {
+          // Collect branch weights into a vector.
+          SmallVector<uint32_t, 8> Weights;
+          for (unsigned MD_i = 1, MD_e = MD->getNumOperands(); MD_i < MD_e;
+               ++MD_i) {
+            ConstantInt* CI = dyn_cast<ConstantInt>(MD->getOperand(MD_i));
+            assert(CI);
+            Weights.push_back(CI->getValue().getZExtValue());
+          }
+          // Merge weight of this case to the default weight.
+          unsigned idx = i.getCaseIndex();
+          Weights[0] += Weights[idx+1];
+          // Remove weight for this case.
+          std::swap(Weights[idx+1], Weights.back());
+          Weights.pop_back();
+          SI->setMetadata(LLVMContext::MD_prof,
+                          MDBuilder(BB->getContext()).
+                          createBranchWeights(Weights));
+        }
         // Remove this entry.
         DefaultDest->removePredecessor(SI->getParent());
         SI->removeCase(i);

diff --git a/test/Transforms/SimplifyCFG/preserve-branchweights.ll b/test/Transforms/SimplifyCFG/preserve-branchweights.ll
index c7917857ee605b6b3ab791b01ee4eae465653d2c..71b27809ff86698e9e26694b2a0465762eb6eeb0 100644 (file)
--- a/test/Transforms/SimplifyCFG/preserve-branchweights.ll
+++ b/test/Transforms/SimplifyCFG/preserve-branchweights.ll
@@ -79,10 +79,42 @@ Z:
   ret void
 }
 
+;; test5 - The case where it jumps to the default target will be removed.
+define void @test5(i32 %M, i32 %N) nounwind uwtable {
+entry:
+  switch i32 %N, label %sw2 [
+    i32 1, label %sw2
+    i32 2, label %sw.bb
+    i32 3, label %sw.bb1
+  ], !prof !3
+; CHECK: test5
+; CHECK: switch i32 %N, label %sw2 [
+; CHECK: i32 3, label %sw.bb1
+; CHECK: i32 2, label %sw.bb
+; CHECK: ], !prof !2
+
+sw.bb:
+  call void @helper(i32 0)
+  br label %sw.epilog
+
+sw.bb1:
+  call void @helper(i32 1)
+  br label %sw.epilog
+
+sw2:
+  call void @helper(i32 2)
+  br label %sw.epilog
+
+sw.epilog:
+  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}
 
 ; CHECK: !0 = metadata !{metadata !"branch_weights", i32 5, i32 11}
 ; CHECK: !1 = metadata !{metadata !"branch_weights", i32 1, i32 5}
-; CHECK-NOT: !2
+; CHECK: !2 = metadata !{metadata !"branch_weights", i32 7, i32 1, i32 2}
+; CHECK-NOT: !3