[ConstraintElimination] Add upper bound info based on maximum type bounds for zext instructions

[zjaffal]

Summary

Utilize the new BoundInfo to optimize zext operations during decomposition by assigning an upperBound to zext based on the max value of the pre-zext width.

[zjaffal]

Add condition to prevent generating upperbounds for variables with bitwidth > 64

[zjaffal]

ping

llvm/lib/Transforms/Scalar/ConstraintElimination.cpp

if (auto *CI = dyn_cast<ConstantInt>(V)) {
     return int64_t(CI->getZExtValue());
   }
 
   if (auto *GEP = dyn_cast<GEPOperator>(V))
     return decomposeGEP(*GEP, Preconditions, IsSigned, DL);
 
   Value *Op0;
   bool IsKnownNonNegative = false;
+  int64_t UpperBoundVal = MaxConstraintValue;
   if (match(V, m_ZExt(m_Value(Op0)))) {
     IsKnownNonNegative = true;
     V = Op0;
+    if (!llvm::any_of(V->users(),
+                      [&](User *User) { return isa<SExtInst>(User); })) {
+      TypeSize PreZextWidth =
+          DL.getTypeSizeInBits(V->getType()->getScalarType());
+      if (PreZextWidth <= 64)
+        UpperBoundVal = APInt::getMaxValue(PreZextWidth).getZExtValue();
+    }
   }
 
   Value *Op1;
   ConstantInt *CI;
   if (match(V, m_NUWAdd(m_Value(Op0), m_Value(Op1)))) {
     return MergeResults(Op0, Op1, IsSigned);
   }
   if (match(V, m_NSWAdd(m_Value(Op0), m_Value(Op1)))) {
if (match(V, m_NUWMul(m_Value(Op1), m_ConstantInt(CI))) && canUseSExt(CI) &&
     return Result;
   }
 
   if (match(V, m_NUWSub(m_Value(Op0), m_ConstantInt(CI))) && canUseSExt(CI))
     return {-1 * CI->getSExtValue(), {{1, Op0}}};
   if (match(V, m_NUWSub(m_Value(Op0), m_Value(Op1))))
     return {0, {{1, Op0}, {-1, Op1}}};
 
-  return {V, IsKnownNonNegative};
+  return {V, IsKnownNonNegative, UpperBoundVal};
 }
 
 ConstraintTy
 ConstraintInfo::getConstraint(CmpInst::Predicate Pred, Value *Op0, Value *Op1,
                               SmallVectorImpl<Value *> &NewVariables) const {
   assert(NewVariables.empty() && "NewVariables must be empty when passed in");
   bool IsEq = false;
   // Try to convert Pred to one of ULE/SLT/SLE/SLT.

llvm/test/Transforms/ConstraintElimination/type-bounds.ll

 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
 ; RUN: opt -passes=constraint-elimination -S %s | FileCheck %s
 
 declare void @use(i1)
 
 define void @zext_cmp_i1_to_i32(i1 %a, i32 %b) {
 ; CHECK-LABEL: @zext_cmp_i1_to_i32(
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[INIT_COND:%.*]] = icmp ugt i1 [[A:%.*]], false
 ; CHECK-NEXT:    br i1 [[INIT_COND]], label [[PRE_COND:%.*]], label [[EXIT:%.*]]
 ; CHECK:       pre.cond:
 ; CHECK-NEXT:    [[A_EXT:%.*]] = zext i1 [[A]] to i32
 ; CHECK-NEXT:    [[CMP_1:%.*]] = icmp ugt i32 [[B:%.*]], 1
 ; CHECK-NEXT:    br i1 [[CMP_1]], label [[COND:%.*]], label [[EXIT]]
 ; CHECK:       cond:
 ; CHECK-NEXT:    [[CMP_2:%.*]] = icmp ult i32 [[A_EXT]], [[B]]
-; CHECK-NEXT:    call void @use(i1 [[CMP_2]])
+; CHECK-NEXT:    call void @use(i1 true)
 ; CHECK-NEXT:    ret void
 ; CHECK:       exit:
 ; CHECK-NEXT:    ret void
 ;
 entry:
   %init.cond = icmp ugt i1 %a, false
   br i1 %init.cond, label %pre.cond, label %exit
 

 ; CHECK-NEXT:    [[INIT_COND:%.*]] = icmp ugt i8 [[A:%.*]], 0
 ; CHECK-NEXT:    br i1 [[INIT_COND]], label [[PRE_COND:%.*]], label [[EXIT:%.*]]
 ; CHECK:       pre.cond:
 ; CHECK-NEXT:    [[A_EXT:%.*]] = zext i8 [[A]] to i32
 ; CHECK-NEXT:    [[CMP_1:%.*]] = icmp ugt i32 [[B:%.*]], 255
 ; CHECK-NEXT:    br i1 [[CMP_1]], label [[COND:%.*]], label [[EXIT]]
 ; CHECK:       cond:
 ; CHECK-NEXT:    [[CMP_2:%.*]] = icmp ult i32 [[A_EXT]], [[B]]
-; CHECK-NEXT:    call void @use(i1 [[CMP_2]])
+; CHECK-NEXT:    call void @use(i1 true)
 ; CHECK-NEXT:    ret void
 ; CHECK:       exit:
 ; CHECK-NEXT:    ret void
 ;
 entry:
   %init.cond = icmp ugt i8 %a, 0
   br i1 %init.cond, label %pre.cond, label %exit
 

 ; CHECK-NEXT:    [[A2_EXT:%.*]] = zext i8 [[A]] to i32
 ; CHECK-NEXT:    [[CMP_1:%.*]] = icmp ugt i32 [[B:%.*]], 255
 ; CHECK-NEXT:    [[CMP_2:%.*]] = icmp ugt i32 [[B2:%.*]], 255
 ; CHECK-NEXT:    [[PRE_CMP:%.*]] = and i1 [[CMP_1]], [[CMP_2]]
 ; CHECK-NEXT:    br i1 [[PRE_CMP]], label [[COND:%.*]], label [[EXIT]]
 ; CHECK:       cond:
 ; CHECK-NEXT:    [[CMP_3:%.*]] = icmp ult i32 [[A_EXT]], [[B]]
 ; CHECK-NEXT:    [[CMP_4:%.*]] = icmp ult i32 [[A2_EXT]], [[B2]]
-; CHECK-NEXT:    call void @use(i1 [[CMP_3]])
-; CHECK-NEXT:    call void @use(i1 [[CMP_4]])
+; CHECK-NEXT:    call void @use(i1 true)
+; CHECK-NEXT:    call void @use(i1 true)
 ; CHECK-NEXT:    ret void
 ; CHECK:       exit:
 ; CHECK-NEXT:    ret void
 ;
 entry:
   %init.cond = icmp ugt i8 %a, 0
   br i1 %init.cond, label %pre.cond, label %exit