[ValueTracking] Honour recursion limit.

The recently improved support for `icmp` in ValueTracking
(r307304) exposes the fact that `isImplied` condition doesn't
really bail out if we hit the recursion limit (and calls
`computeKnownBits` which increases the depth and asserts).

Differential Revision:  https://reviews.llvm.org/D36512

llvm-svn: 310481

1 files changed, 4 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 5372d9dc7c2..995b3e0c6de 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -4556,6 +4556,10 @@ static Optional<bool> isImpliedCondAndOr(const BinaryOperator *LHS,
 Optional<bool> llvm::isImpliedCondition(const Value *LHS, const Value *RHS,
                                         const DataLayout &DL, bool LHSIsTrue,
                                         unsigned Depth) {
+  // Bail out when we hit the limit.
+  if (Depth == MaxDepth)
+    return None;
+
   // A mismatch occurs when we compare a scalar cmp to a vector cmp, for
   // example.
   if (LHS->getType() != RHS->getType())