[ValueTracking] add helper function for testing implied condition; NFCI

We were duplicating code around the existing isImpliedCondition() that
checks for a predecessor block/dominating condition, so make that a
wrapper call.

llvm-svn: 348088

1 files changed, 32 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 3c01d979560..a6ad6bf8cae 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -5378,3 +5378,35 @@ Optional<bool> llvm::isImpliedCondition(const Value *LHS, const Value *RHS,
   }
   return None;
 }
+
+Optional<bool> llvm::isImpliedByDomCondition(const Value *Cond,
+                                             const Instruction *ContextI,
+                                             const DataLayout &DL) {
+  assert(Cond->getType()->isIntOrIntVectorTy(1) && "Condition must be bool");
+  if (!ContextI || !ContextI->getParent())
+    return None;
+
+  // TODO: This is a poor/cheap way to determine dominance. Should we use a
+  // dominator tree (eg, from a SimplifyQuery) instead?
+  const BasicBlock *ContextBB = ContextI->getParent();
+  const BasicBlock *PredBB = ContextBB->getSinglePredecessor();
+  if (!PredBB)
+    return None;
+
+  // We need a conditional branch in the predecessor.
+  Value *PredCond;
+  BasicBlock *TrueBB, *FalseBB;
+  if (!match(PredBB->getTerminator(), m_Br(m_Value(PredCond), TrueBB, FalseBB)))
+    return None;
+
+  // The branch should get simplified. Don't bother simplifying this condition.
+  if (TrueBB == FalseBB)
+    return None;
+
+  assert((TrueBB == ContextBB || FalseBB == ContextBB) &&
+         "Predecessor block does not point to successor?");
+
+  // Is this condition implied by the predecessor condition?
+  bool CondIsTrue = TrueBB == ContextBB;
+  return isImpliedCondition(PredCond, Cond, DL, CondIsTrue);
+}