IR: introduce struct with CmpInst::Predicate and samesign (#116867)

Introduce llvm::CmpPredicate, an abstraction over a floating-point
predicate, and a pack of an integer predicate with samesign information,
in order to ease extending large portions of the codebase that take a
CmpInst::Predicate to respect the samesign flag.

We have chosen to demonstrate the utility of this new abstraction by
migrating parts of ValueTracking, InstructionSimplify, and InstCombine
from CmpInst::Predicate to llvm::CmpPredicate. There should be no
functional changes, as we don't perform any extra optimizations with
samesign in this patch, or use CmpPredicate::getMatching.

The design approach taken by this patch allows for unaudited callers of
APIs that take a llvm::CmpPredicate to silently drop the samesign
information; it does not pose a correctness issue, and allows us to
migrate the codebase piece-wise.

Author: artagnon

llvm/include/llvm/Analysis/InstSimplifyFolder.h

@@ -22,6 +22,7 @@
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/Analysis/InstructionSimplify.h"
 #include "llvm/Analysis/TargetFolder.h"
+#include "llvm/IR/CmpPredicate.h"
 #include "llvm/IR/IRBuilderFolder.h"
 #include "llvm/IR/Instruction.h"
 

llvm/include/llvm/Analysis/InstructionSimplify.h

@@ -44,6 +44,7 @@ class DataLayout;
 class DominatorTree;
 class Function;
 class Instruction;
+class CmpPredicate;
 class LoadInst;
 struct LoopStandardAnalysisResults;
 class Pass;
@@ -152,11 +153,11 @@ Value *simplifyOrInst(Value *LHS, Value *RHS, const SimplifyQuery &Q);
 Value *simplifyXorInst(Value *LHS, Value *RHS, const SimplifyQuery &Q);
 
 /// Given operands for an ICmpInst, fold the result or return null.
-Value *simplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
+Value *simplifyICmpInst(CmpPredicate Pred, Value *LHS, Value *RHS,
                         const SimplifyQuery &Q);
 
 /// Given operands for an FCmpInst, fold the result or return null.
-Value *simplifyFCmpInst(unsigned Predicate, Value *LHS, Value *RHS,
+Value *simplifyFCmpInst(CmpPredicate Predicate, Value *LHS, Value *RHS,
                         FastMathFlags FMF, const SimplifyQuery &Q);
 
 /// Given operands for a SelectInst, fold the result or return null.
@@ -200,7 +201,7 @@ Value *simplifyShuffleVectorInst(Value *Op0, Value *Op1, ArrayRef<int> Mask,
 //=== Helper functions for higher up the class hierarchy.
 
 /// Given operands for a CmpInst, fold the result or return null.
-Value *simplifyCmpInst(unsigned Predicate, Value *LHS, Value *RHS,
+Value *simplifyCmpInst(CmpPredicate Predicate, Value *LHS, Value *RHS,
                        const SimplifyQuery &Q);
 
 /// Given operand for a UnaryOperator, fold the result or return null.

llvm/include/llvm/Analysis/ValueTracking.h

@@ -1255,8 +1255,7 @@ std::optional<bool> isImpliedCondition(const Value *LHS, const Value *RHS,
                                        const DataLayout &DL,
                                        bool LHSIsTrue = true,
                                        unsigned Depth = 0);
-std::optional<bool> isImpliedCondition(const Value *LHS,
-                                       CmpInst::Predicate RHSPred,
+std::optional<bool> isImpliedCondition(const Value *LHS, CmpPredicate RHSPred,
                                        const Value *RHSOp0, const Value *RHSOp1,
                                        const DataLayout &DL,
                                        bool LHSIsTrue = true,
@@ -1267,8 +1266,8 @@ std::optional<bool> isImpliedCondition(const Value *LHS,
 std::optional<bool> isImpliedByDomCondition(const Value *Cond,
                                             const Instruction *ContextI,
                                             const DataLayout &DL);
-std::optional<bool> isImpliedByDomCondition(CmpInst::Predicate Pred,
-                                            const Value *LHS, const Value *RHS,
+std::optional<bool> isImpliedByDomCondition(CmpPredicate Pred, const Value *LHS,
+                                            const Value *RHS,
                                             const Instruction *ContextI,
                                             const DataLayout &DL);
 

llvm/include/llvm/IR/CmpPredicate.h

@@ -0,0 +1,62 @@
+//===- CmpPredicate.h - CmpInst Predicate with samesign information -------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// A CmpInst::Predicate with any samesign information (applicable to ICmpInst).
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_IR_CMPPREDICATE_H
+#define LLVM_IR_CMPPREDICATE_H
+
+#include "llvm/IR/InstrTypes.h"
+
+namespace llvm {
+/// An abstraction over a floating-point predicate, and a pack of an integer
+/// predicate with samesign information. Some functions in ICmpInst construct
+/// and return this type in place of a Predicate.
+class CmpPredicate {
+  CmpInst::Predicate Pred;
+  bool HasSameSign;
+
+public:
+  /// Constructed implictly with a either Predicate and samesign information, or
+  /// just a Predicate, dropping samesign information.
+  CmpPredicate(CmpInst::Predicate Pred, bool HasSameSign = false)
+      : Pred(Pred), HasSameSign(HasSameSign) {
+    assert(!HasSameSign || CmpInst::isIntPredicate(Pred));
+  }
+
+  /// Implictly converts to the underlying Predicate, dropping samesign
+  /// information.
+  operator CmpInst::Predicate() const { return Pred; }
+
+  /// Query samesign information, for optimizations.
+  bool hasSameSign() const { return HasSameSign; }
+
+  /// Compares two CmpPredicates taking samesign into account and returns the
+  /// canonicalized CmpPredicate if they match. An alternative to operator==.
+  ///
+  /// For example,
+  ///   samesign ult + samesign ult -> samesign ult
+  ///   samesign ult + ult -> ult
+  ///   samesign ult + slt -> slt
+  ///   ult + ult -> ult
+  ///   ult + slt -> std::nullopt
+  static std::optional<CmpPredicate> getMatching(CmpPredicate A,
+                                                 CmpPredicate B);
+
+  /// An operator== on the underlying Predicate.
+  bool operator==(CmpInst::Predicate P) const { return Pred == P; }
+
+  /// There is no operator== defined on CmpPredicate. Use getMatching instead to
+  /// get the canonicalized matching CmpPredicate.
+  bool operator==(CmpPredicate) const = delete;
+};
+} // namespace llvm
+
+#endif

llvm/include/llvm/IR/Instructions.h

@@ -24,6 +24,7 @@
 #include "llvm/ADT/iterator.h"
 #include "llvm/ADT/iterator_range.h"
 #include "llvm/IR/CFG.h"
+#include "llvm/IR/CmpPredicate.h"
 #include "llvm/IR/Constant.h"
 #include "llvm/IR/DerivedTypes.h"
 #include "llvm/IR/GEPNoWrapFlags.h"
@@ -1203,6 +1204,33 @@ class ICmpInst: public CmpInst {
 #endif
   }
 
+  /// @returns the predicate along with samesign information.
+  CmpPredicate getCmpPredicate() const {
+    return {getPredicate(), hasSameSign()};
+  }
+
+  /// @returns the inverse predicate along with samesign information: static
+  /// variant.
+  static CmpPredicate getInverseCmpPredicate(CmpPredicate Pred) {
+    return {getInversePredicate(Pred), Pred.hasSameSign()};
+  }
+
+  /// @returns the inverse predicate along with samesign information.
+  CmpPredicate getInverseCmpPredicate() const {
+    return getInverseCmpPredicate(getCmpPredicate());
+  }
+
+  /// @returns the swapped predicate along with samesign information: static
+  /// variant.
+  static CmpPredicate getSwappedCmpPredicate(CmpPredicate Pred) {
+    return {getSwappedPredicate(Pred), Pred.hasSameSign()};
+  }
+
+  /// @returns the swapped predicate.
+  Predicate getSwappedCmpPredicate() const {
+    return getSwappedPredicate(getCmpPredicate());
+  }
+
   /// For example, EQ->EQ, SLE->SLE, UGT->SGT, etc.
   /// @returns the predicate that would be the result if the operand were
   /// regarded as signed.
@@ -1212,7 +1240,7 @@ class ICmpInst: public CmpInst {
   }
 
   /// Return the signed version of the predicate: static variant.
-  static Predicate getSignedPredicate(Predicate pred);
+  static Predicate getSignedPredicate(Predicate Pred);
 
   /// For example, EQ->EQ, SLE->ULE, UGT->UGT, etc.
   /// @returns the predicate that would be the result if the operand were
@@ -1223,14 +1251,15 @@ class ICmpInst: public CmpInst {
   }
 
   /// Return the unsigned version of the predicate: static variant.
-  static Predicate getUnsignedPredicate(Predicate pred);
+  static Predicate getUnsignedPredicate(Predicate Pred);
 
-  /// For example, SLT->ULT, ULT->SLT, SLE->ULE, ULE->SLE, EQ->Failed assert
+  /// For example, SLT->ULT, ULT->SLT, SLE->ULE, ULE->SLE, EQ->EQ
   /// @returns the unsigned version of the signed predicate pred or
   ///          the signed version of the signed predicate pred.
-  static Predicate getFlippedSignednessPredicate(Predicate pred);
+  /// Static variant.
+  static Predicate getFlippedSignednessPredicate(Predicate Pred);
 
-  /// For example, SLT->ULT, ULT->SLT, SLE->ULE, ULE->SLE, EQ->Failed assert
+  /// For example, SLT->ULT, ULT->SLT, SLE->ULE, ULE->SLE, EQ->EQ
   /// @returns the unsigned version of the signed predicate pred or
   ///          the signed version of the signed predicate pred.
   Predicate getFlippedSignednessPredicate() const {

llvm/include/llvm/Transforms/InstCombine/InstCombiner.h

@@ -157,7 +157,7 @@ class LLVM_LIBRARY_VISIBILITY InstCombiner {
   /// conditional branch or select to create a compare with a canonical
   /// (inverted) predicate which is then more likely to be matched with other
   /// values.
-  static bool isCanonicalPredicate(CmpInst::Predicate Pred) {
+  static bool isCanonicalPredicate(CmpPredicate Pred) {
     switch (Pred) {
     case CmpInst::ICMP_NE:
     case CmpInst::ICMP_ULE:
@@ -185,10 +185,9 @@ class LLVM_LIBRARY_VISIBILITY InstCombiner {
   }
 
   std::optional<std::pair<
-      CmpInst::Predicate,
-      Constant *>> static getFlippedStrictnessPredicateAndConstant(CmpInst::
-                                                                       Predicate
-                                                                           Pred,
+      CmpPredicate,
+      Constant *>> static getFlippedStrictnessPredicateAndConstant(CmpPredicate
+                                                                       Pred,
                                                                    Constant *C);
 
   static bool shouldAvoidAbsorbingNotIntoSelect(const SelectInst &SI) {