[llvm] r266987 - Refactor implied condition logic from ValueTracking directly into CmpInst. NFC.

Chad Rosier via llvm-commits llvm-commits at lists.llvm.org
Thu Apr 21 08:57:38 PDT 2016


Hi Philip,
I agree it's difficult to come up with a meaningful name.  How about isImpliedTrueByMatchingCmp/isImpliedFalseByMatchingCmp?

 Chad

-----Original Message-----
From: Philip Reames [mailto:listmail at philipreames.com] 
Sent: Thursday, April 21, 2016 10:48 AM
To: Chad Rosier <mcrosier at codeaurora.org>; llvm-commits at lists.llvm.org
Subject: Re: [llvm] r266987 - Refactor implied condition logic from ValueTracking directly into CmpInst. NFC.

The naming of isTrueWhenOperandsMatch and isFalseWhenOperandsMatch 
aren't exactly clear.  Reading through code, I'd have no idea what they 
do.  Possibly: isImpliedByMatchingCompare(Pred)?  I don't really like 
that either, but its better than what we have.

Philip


On 04/21/2016 07:04 AM, Chad Rosier via llvm-commits wrote:
> Author: mcrosier
> Date: Thu Apr 21 09:04:54 2016
> New Revision: 266987
>
> URL: http://llvm.org/viewvc/llvm-project?rev=266987&view=rev
> Log:
> Refactor implied condition logic from ValueTracking directly into CmpInst. NFC.
>
> Differential Revision: http://reviews.llvm.org/D19330
>
> Modified:
>      llvm/trunk/include/llvm/IR/InstrTypes.h
>      llvm/trunk/lib/Analysis/ValueTracking.cpp
>      llvm/trunk/lib/IR/Instructions.cpp
>
> Modified: llvm/trunk/include/llvm/IR/InstrTypes.h
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/IR/InstrTypes.h?rev=266987&r1=266986&r2=266987&view=diff
> ==============================================================================
> --- llvm/trunk/include/llvm/IR/InstrTypes.h (original)
> +++ llvm/trunk/include/llvm/IR/InstrTypes.h Thu Apr 21 09:04:54 2016
> @@ -1067,6 +1067,18 @@ public:
>       return isFalseWhenEqual(getPredicate());
>     }
>   
> +  /// @brief Determine if Pred1 implies Pred2 is true when two compares have
> +  /// matching operands.
> +  bool isTrueWhenOperandsMatch(Predicate Pred2) {
> +    return isTrueWhenOperandsMatch(getPredicate(), Pred2);
> +  }
> +
> +  /// @brief Determine if Pred1 implies Pred2 is false when two compares have
> +  /// matching operands.
> +  bool isFalseWhenOperandsMatch(Predicate Pred2) {
> +    return isFalseWhenOperandsMatch(getPredicate(), Pred2);
> +  }
> +
>     /// @returns true if the predicate is unsigned, false otherwise.
>     /// @brief Determine if the predicate is an unsigned operation.
>     static bool isUnsigned(Predicate predicate);
> @@ -1087,6 +1099,14 @@ public:
>     /// Determine if the predicate is false when comparing a value with itself.
>     static bool isFalseWhenEqual(Predicate predicate);
>   
> +  /// Determine if Pred1 implies Pred2 is true when two compares have matching
> +  /// operands.
> +  static bool isTrueWhenOperandsMatch(Predicate Pred1, Predicate Pred2);
> +
> +  /// Determine if Pred1 implies Pred2 is false when two compares have matching
> +  /// operands.
> +  static bool isFalseWhenOperandsMatch(Predicate Pred1, Predicate Pred2);
> +
>     /// @brief Methods for support type inquiry through isa, cast, and dyn_cast:
>     static inline bool classof(const Instruction *I) {
>       return I->getOpcode() == Instruction::ICmp ||
>
> Modified: llvm/trunk/lib/Analysis/ValueTracking.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ValueTracking.cpp?rev=266987&r1=266986&r2=266987&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Analysis/ValueTracking.cpp (original)
> +++ llvm/trunk/lib/Analysis/ValueTracking.cpp Thu Apr 21 09:04:54 2016
> @@ -3935,61 +3935,11 @@ static Optional<bool> isImpliedCondMatch
>       std::swap(BLHS, BRHS);
>       BPred = ICmpInst::getSwappedPredicate(BPred);
>     }
> -
> -  // If the predicates match, then we know the first condition implies the
> -  // second is true.
> -  if (APred == BPred)
> +  if (CmpInst::isTrueWhenOperandsMatch(APred, BPred))
>       return true;
> -
> -  // If an inverted APred matches BPred, we can infer the second condition is
> -  // false.
> -  if (CmpInst::getInversePredicate(APred) == BPred)
> +  if (CmpInst::isFalseWhenOperandsMatch(APred, BPred))
>       return false;
>   
> -  // If a swapped APred matches BPred, we can infer the second condition is
> -  // false in many cases.
> -  if (CmpInst::getSwappedPredicate(APred) == BPred) {
> -    switch (APred) {
> -    default:
> -      break;
> -    case CmpInst::ICMP_UGT: // A >u B implies A <u B is false.
> -    case CmpInst::ICMP_ULT: // A <u B implies A >u B is false.
> -    case CmpInst::ICMP_SGT: // A >s B implies A <s B is false.
> -    case CmpInst::ICMP_SLT: // A <s B implies A >s B is false.
> -      return false;
> -    }
> -  }
> -
> -  // The predicates must match sign or at least one of them must be an equality
> -  // comparison (which is signless).
> -  if (ICmpInst::isSigned(APred) != ICmpInst::isSigned(BPred) &&
> -      !ICmpInst::isEquality(APred) && !ICmpInst::isEquality(BPred))
> -    return None;
> -
> -  switch (APred) {
> -  default:
> -    break;
> -  case CmpInst::ICMP_EQ:
> -    // A == B implies A > B and A < B are false.
> -    if (CmpInst::isFalseWhenEqual(BPred))
> -      return false;
> -
> -    break;
> -  case CmpInst::ICMP_UGT:
> -  case CmpInst::ICMP_ULT:
> -  case CmpInst::ICMP_SGT:
> -  case CmpInst::ICMP_SLT:
> -    // A > B implies A == B is false.
> -    // A < B implies A == B is false.
> -    if (BPred == CmpInst::ICMP_EQ)
> -      return false;
> -
> -    // A > B implies A != B is true.
> -    // A < B implies A != B is true.
> -    if (BPred == CmpInst::ICMP_NE)
> -      return true;
> -    break;
> -  }
>     return None;
>   }
>   
>
> Modified: llvm/trunk/lib/IR/Instructions.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/IR/Instructions.cpp?rev=266987&r1=266986&r2=266987&view=diff
> ==============================================================================
> --- llvm/trunk/lib/IR/Instructions.cpp (original)
> +++ llvm/trunk/lib/IR/Instructions.cpp Thu Apr 21 09:04:54 2016
> @@ -3597,6 +3597,58 @@ bool CmpInst::isFalseWhenEqual(Predicate
>     }
>   }
>   
> +bool CmpInst::isTrueWhenOperandsMatch(Predicate Pred1, Predicate Pred2) {
> +  // If the predicates match, then we know the first condition implies the
> +  // second is true.
> +  if (Pred1 == Pred2)
> +    return true;
> +
> +  switch (Pred1) {
> +  default:
> +    break;
> +  case ICMP_UGT: // A >u B implies A != B is true.
> +  case ICMP_ULT: // A <u B implies A != B is true.
> +  case ICMP_SGT: // A >s B implies A != B is true.
> +  case ICMP_SLT: // A <s B implies A != B is true.
> +    return Pred2 == ICMP_NE;
> +  }
> +  return false;
> +}
> +
> +bool CmpInst::isFalseWhenOperandsMatch(Predicate Pred1, Predicate Pred2) {
> +  // If an inverted Pred1 matches Pred2, we can infer the second condition is
> +  // false.
> +  if (getInversePredicate(Pred1) == Pred2)
> +    return true;
> +
> +  // If a swapped Pred1 matches Pred2, we can infer the second condition is
> +  // false in many cases.
> +  if (getSwappedPredicate(Pred1) == Pred2) {
> +    switch (Pred1) {
> +    default:
> +      break;
> +    case ICMP_UGT: // A >u B implies A <u B is false.
> +    case ICMP_ULT: // A <u B implies A >u B is false.
> +    case ICMP_SGT: // A >s B implies A <s B is false.
> +    case ICMP_SLT: // A <s B implies A >s B is false.
> +      return true;
> +    }
> +  }
> +  // A == B implies A > B and A < B are false.
> +  if (Pred1 == ICMP_EQ && isFalseWhenEqual(Pred2))
> +    return true;
> +
> +  switch (Pred1) {
> +  default:
> +    break;
> +  case ICMP_UGT: // A >u B implies A == B is false.
> +  case ICMP_ULT: // A <u B implies A == B is false.
> +  case ICMP_SGT: // A >s B implies A == B is false.
> +  case ICMP_SLT: // A <s B implies A == B is false.
> +    return Pred2 == ICMP_EQ;
> +  }
> +  return false;
> +}
>   
>   //===----------------------------------------------------------------------===//
>   //                        SwitchInst Implementation
>
>
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