1 files changed, 22 insertions, 1 deletions
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index c62b4d6cdd9..80b1957a7e2 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -79,6 +79,13 @@ static cl::opt<unsigned> UnfoldElementAtomicMemcpyMaxElements(
     cl::desc("Maximum number of elements in atomic memcpy the optimizer is "
              "allowed to unfold"));
 
+static cl::opt<unsigned> GuardWideningWindow(
+    "instcombine-guard-widening-window",
+    cl::init(3),
+    cl::desc("How wide an instruction window to bypass looking for "
+             "another guard"));
+
+
 /// Return the specified type promoted as it would be to pass though a va_arg
 /// area.
 static Type *getPromotedType(Type *Ty) {
@@ -3624,8 +3631,16 @@ Instruction *InstCombiner::visitCallInst(CallInst &CI) {
   }
 
   case Intrinsic::experimental_guard: {
-    // Is this guard followed by another guard?
+    // Is this guard followed by another guard?  We scan forward over a small
+    // fixed window of instructions to handle common cases with conditions
+    // computed between guards.
     Instruction *NextInst = II->getNextNode();
+    for (int i = 0; i < GuardWideningWindow; i++) {
+      // Note: Using context-free form to avoid compile time blow up
+      if (!isSafeToSpeculativelyExecute(NextInst))
+        break;
+      NextInst = NextInst->getNextNode();
+    }
     Value *NextCond = nullptr;
     if (match(NextInst,
               m_Intrinsic<Intrinsic::experimental_guard>(m_Value(NextCond)))) {
@@ -3636,6 +3651,12 @@ Instruction *InstCombiner::visitCallInst(CallInst &CI) {
         return eraseInstFromFunction(*NextInst);
 
       // Otherwise canonicalize guard(a); guard(b) -> guard(a & b).
+      Instruction* MoveI = II->getNextNode();
+      while (MoveI != NextInst) {
+        auto *Temp = MoveI;
+        MoveI = MoveI->getNextNode();
+        Temp->moveBefore(II);
+      }
       II->setArgOperand(0, Builder.CreateAnd(CurrCond, NextCond));
       return eraseInstFromFunction(*NextInst);
     }