[InstCombine] Optimize icmp slt signum(x), 1 --> icmp slt x, 1

[oota-llvm.git] / include / llvm / IR / PatternMatch.h

diff --git a/include/llvm/IR/PatternMatch.h b/include/llvm/IR/PatternMatch.h
index 41154e6441a93b9c3c1b42e9959eb2f84bb4a538..f4d7d8c4441628c35d137039eda8cae860a72337 100644 (file)
--- a/include/llvm/IR/PatternMatch.h
+++ b/include/llvm/IR/PatternMatch.h
@@ -1272,6 +1272,46 @@ inline typename m_Intrinsic_Ty<Opnd0, Opnd1>::Ty m_FMax(const Opnd0 &Op0,
   return m_Intrinsic<Intrinsic::maxnum>(Op0, Op1);
 }
 
+template <typename Opnd_t> struct Signum_match {
+  Opnd_t Val;
+  Signum_match(const Opnd_t &V) : Val(V) {}
+
+  template <typename OpTy> bool match(OpTy *V) {
+    unsigned TypeSize = V->getType()->getScalarSizeInBits();
+    if (TypeSize == 0)
+      return false;
+
+    unsigned ShiftWidth = TypeSize - 1;
+    Value *OpL = nullptr, *OpR = nullptr;
+
+    // This is the representation of signum we match:
+    //
+    //  signum(x) == (x >> 63) | (-x >>u 63)
+    //
+    // An i1 value is its own signum, so it's correct to match
+    //
+    //  signum(x) == (x >> 0)  | (-x >>u 0)
+    //
+    // for i1 values.
+
+    auto LHS = m_AShr(m_Value(OpL), m_SpecificInt(ShiftWidth));
+    auto RHS = m_LShr(m_Neg(m_Value(OpR)), m_SpecificInt(ShiftWidth));
+    auto Signum = m_Or(LHS, RHS);
+
+    return Signum.match(V) && OpL == OpR && Val.match(OpL);
+  }
+};
+
+/// \brief Matches a signum pattern.
+///
+/// signum(x) =
+///      x >  0  ->  1
+///      x == 0  ->  0
+///      x <  0  -> -1
+template <typename Val_t> inline Signum_match<Val_t> m_Signum(const Val_t &V) {
+  return Signum_match<Val_t>(V);
+}
+
 } // end namespace PatternMatch
 } // end namespace llvm