[ValueTracking] Expose `implies` via ValueTracking, NFC

[sanjoy]

Summary

This will allow a later patch to JumpThreading use this functionality.

[majnemer]

lib/Analysis/ValueTracking.cpp

3944 ↗

(On Diff #38086)

Does this need to be here? add nuw can never decrease a number in unsigned-comparison space.

[sanjoy]

lib/Analysis/ValueTracking.cpp

3944 ↗

(On Diff #38086)

You're right, but I'm only moving the code, and I'd rather have this change not have any semantic effects.

I'll fix this up in a later commit.

[hfinkel]

LGTM.

llvm/trunk/include/llvm/Analysis/ValueTracking.h

namespace llvm {
   SelectPatternResult matchSelectPattern(Value *V, Value *&LHS, Value *&RHS,
                                          Instruction::CastOps *CastOp = nullptr);
 
   /// Parse out a conservative ConstantRange from !range metadata.
   ///
   /// E.g. if RangeMD is !{i32 0, i32 10, i32 15, i32 20} then return [0, 20).
   ConstantRange getConstantRangeFromMetadata(MDNode &RangeMD);
 
+  /// Return true if RHS is known to be implied by LHS.  A & B must be i1
+  /// (boolean) values or a vector of such values. Note that the truth table for
+  /// implication is the same as <=u on i1 values (but not <=s!).  The truth
+  /// table for both is:
+  ///    | T | F (B)
+  ///  T | T | F
+  ///  F | T | T
+  /// (A)
+  bool isImpliedCondition(Value *LHS, Value *RHS);
 } // end namespace llvm
 
 #endif

llvm/trunk/lib/Analysis/InstructionSimplify.cpp

if ((IsNAC(LHSUObjs) && IsAllocDisjoint(RHSUObjs)) ||
         return ConstantInt::get(GetCompareTy(LHS),
                                 !CmpInst::isTrueWhenEqual(Pred));
   }
 
   // Otherwise, fail.
   return nullptr;
 }
 
-/// Return true if B is known to be implied by A.  A & B must be i1 (boolean)
-/// values or a vector of such values. Note that the truth table for
-/// implication is the same as <=u on i1 values (but not <=s!).  The truth
-/// table for both is: 
-///    | T | F (B)
-///  T | T | F
-///  F | T | T
-/// (A)
-static bool implies(Value *A, Value *B) {
-  assert(A->getType() == B->getType() && "mismatched type");
-  Type *OpTy = A->getType();
-  assert(OpTy->getScalarType()->isIntegerTy(1));
-  
-  // A ==> A by definition
-  if (A == B) return true;
-
-  if (OpTy->isVectorTy())
-    // TODO: extending the code below to handle vectors
-    return false;
-  assert(OpTy->isIntegerTy(1) && "implied by above");
-
-  ICmpInst::Predicate APred, BPred;
-  Value *I;
-  Value *L;
-  ConstantInt *CI;
-  // i +_{nsw} C_{>0} <s L ==> i <s L
-  if (match(A, m_ICmp(APred,
-                      m_NSWAdd(m_Value(I), m_ConstantInt(CI)),
-                      m_Value(L))) &&
-      APred == ICmpInst::ICMP_SLT &&
-      !CI->isNegative() &&
-      match(B, m_ICmp(BPred, m_Specific(I), m_Specific(L))) &&
-      BPred == ICmpInst::ICMP_SLT)
-    return true;
-
-  // i +_{nuw} C_{>0} <u L ==> i <u L
-  if (match(A, m_ICmp(APred,
-                      m_NUWAdd(m_Value(I), m_ConstantInt(CI)),
-                      m_Value(L))) &&
-      APred == ICmpInst::ICMP_ULT &&
-      !CI->isNegative() &&
-      match(B, m_ICmp(BPred, m_Specific(I), m_Specific(L))) &&
-      BPred == ICmpInst::ICMP_ULT)
-    return true;
-
-  return false;
-}
-
 /// SimplifyICmpInst - Given operands for an ICmpInst, see if we can
 /// fold the result.  If not, this returns null.
 static Value *SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
                                const Query &Q, unsigned MaxRecurse) {
   CmpInst::Predicate Pred = (CmpInst::Predicate)Predicate;
   assert(CmpInst::isIntPredicate(Pred) && "Not an integer compare!");
 
   if (Constant *CLHS = dyn_cast<Constant>(LHS)) {
case ICmpInst::ICMP_UGT:
       // X >u 0 -> X
       if (match(RHS, m_Zero()))
         return LHS;
       break;
     case ICmpInst::ICMP_UGE:
       // X >=u 1 -> X
       if (match(RHS, m_One()))
         return LHS;
-      if (implies(RHS, LHS))
+      if (isImpliedCondition(RHS, LHS))
         return getTrue(ITy);
       break;
     case ICmpInst::ICMP_SLT:
       // X <s 0 -> X
       if (match(RHS, m_Zero()))
         return LHS;
       break;
     case ICmpInst::ICMP_SLE:
       // X <=s -1 -> X
       if (match(RHS, m_One()))
         return LHS;
       break;
     case ICmpInst::ICMP_ULE:
-      if (implies(LHS, RHS))
+      if (isImpliedCondition(LHS, RHS))
         return getTrue(ITy);
       break;
     }
   }
 
   // If we are comparing with zero then try hard since this is a common case.
   if (match(RHS, m_Zero())) {
     bool LHSKnownNonNegative, LHSKnownNegative;

llvm/trunk/lib/Analysis/ValueTracking.cpp

for (unsigned i = 1; i < NumRanges; ++i) {
 
     // Note: unionWith will potentially create a range that contains values not
     // contained in any of the original N ranges.
     CR = CR.unionWith(ConstantRange(Low->getValue(), High->getValue()));
   }
 
   return CR;
 }
+
+bool llvm::isImpliedCondition(Value *LHS, Value *RHS) {
+  assert(LHS->getType() == RHS->getType() && "mismatched type");
+  Type *OpTy = LHS->getType();
+  assert(OpTy->getScalarType()->isIntegerTy(1));
+
+  // LHS ==> RHS by definition
+  if (LHS == RHS) return true;
+
+  if (OpTy->isVectorTy())
+    // TODO: extending the code below to handle vectors
+    return false;
+  assert(OpTy->isIntegerTy(1) && "implied by above");
+
+  ICmpInst::Predicate APred, BPred;
+  Value *I;
+  Value *L;
+  ConstantInt *CI;
+  // i +_{nsw} C_{>0} <s L ==> i <s L
+  if (match(LHS, m_ICmp(APred,
+                        m_NSWAdd(m_Value(I), m_ConstantInt(CI)),
+                        m_Value(L))) &&
+      APred == ICmpInst::ICMP_SLT &&
+      !CI->isNegative() &&
+      match(RHS, m_ICmp(BPred, m_Specific(I), m_Specific(L))) &&
+      BPred == ICmpInst::ICMP_SLT)
+    return true;
+
+  // i +_{nuw} C_{>0} <u L ==> i <u L
+  if (match(LHS, m_ICmp(APred,
+                        m_NUWAdd(m_Value(I), m_ConstantInt(CI)),
+                        m_Value(L))) &&
+      APred == ICmpInst::ICMP_ULT &&
+      !CI->isNegative() &&
+      match(RHS, m_ICmp(BPred, m_Specific(I), m_Specific(L))) &&
+      BPred == ICmpInst::ICMP_ULT)
+    return true;
+
+  return false;
+}