Vendor import of llvm release_38 branch r260756:

https://llvm.org/svn/llvm-project/llvm/branches/release_38@260756

1 files changed, 12 insertions, 0 deletions

diff --git a/lib/Transforms/Utils/SimplifyCFG.cpp b/lib/Transforms/Utils/SimplifyCFG.cpp
index 3125a2c..e484b69 100644
--- a/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -90,6 +90,11 @@ static cl::opt<bool> SpeculateOneExpensiveInst(
     cl::desc("Allow exactly one expensive instruction to be speculatively "
              "executed"));
 
+static cl::opt<unsigned> MaxSpeculationDepth(
+    "max-speculation-depth", cl::Hidden, cl::init(10),
+    cl::desc("Limit maximum recursion depth when calculating costs of "
+             "speculatively executed instructions"));
+
 STATISTIC(NumBitMaps, "Number of switch instructions turned into bitmaps");
 STATISTIC(NumLinearMaps, "Number of switch instructions turned into linear mapping");
 STATISTIC(NumLookupTables, "Number of switch instructions turned into lookup tables");
@@ -269,6 +274,13 @@ static bool DominatesMergePoint(Value *V, BasicBlock *BB,
                                 unsigned &CostRemaining,
                                 const TargetTransformInfo &TTI,
                                 unsigned Depth = 0) {
+  // It is possible to hit a zero-cost cycle (phi/gep instructions for example),
+  // so limit the recursion depth.
+  // TODO: While this recursion limit does prevent pathological behavior, it
+  // would be better to track visited instructions to avoid cycles.
+  if (Depth == MaxSpeculationDepth)
+    return false;
+
   Instruction *I = dyn_cast<Instruction>(V);
   if (!I) {
     // Non-instructions all dominate instructions, but not all constantexprs