[inliner] Significantly improve the compile time in cases like PR19499

[oota-llvm.git] / lib / Analysis / IPA / InlineCost.cpp

diff --git a/lib/Analysis/IPA/InlineCost.cpp b/lib/Analysis/IPA/InlineCost.cpp
index c43b5ca250698b45d32a33046f98496c57ec7d45..358f61fd5231480323fc82662e519b98efcad554 100644 (file)
--- a/lib/Analysis/IPA/InlineCost.cpp
+++ b/lib/Analysis/IPA/InlineCost.cpp
@@ -808,9 +808,29 @@ bool CallAnalyzer::visitBranchInst(BranchInst &BI) {
 bool CallAnalyzer::visitSwitchInst(SwitchInst &SI) {
   // We model unconditional switches as free, see the comments on handling
   // branches.
-  return isa<ConstantInt>(SI.getCondition()) ||
-         dyn_cast_or_null<ConstantInt>(
-             SimplifiedValues.lookup(SI.getCondition()));
+  if (isa<ConstantInt>(SI.getCondition()))
+    return true;
+  if (Value *V = SimplifiedValues.lookup(SI.getCondition()))
+    if (isa<ConstantInt>(V))
+      return true;
+
+  // Otherwise, we need to accumulate a cost proportional to the number of
+  // distinct successor blocks. This fan-out in the CFG cannot be represented
+  // for free even if we can represent the core switch as a jumptable that
+  // takes a single instruction.
+  //
+  // NB: We convert large switches which are just used to initialize large phi
+  // nodes to lookup tables instead in simplify-cfg, so this shouldn't prevent
+  // inlining those. It will prevent inlining in cases where the optimization
+  // does not (yet) fire.
+  SmallPtrSet<BasicBlock *, 8> SuccessorBlocks;
+  SuccessorBlocks.insert(SI.getDefaultDest());
+  for (auto I = SI.case_begin(), E = SI.case_end(); I != E; ++I)
+    SuccessorBlocks.insert(I.getCaseSuccessor());
+  // Add cost corresponding to the number of distinct destinations. The first
+  // we model as free because of fallthrough.
+  Cost += (SuccessorBlocks.size() - 1) * InlineConstants::InstrCost;
+  return false;
 }
 
 bool CallAnalyzer::visitIndirectBrInst(IndirectBrInst &IBI) {