[ConstantRange] Add fromKnownBits() method

Following the suggestion in D59450, I'm moving the code for constructing
a ConstantRange from KnownBits out of ValueTracking, which also allows us
to test this code independently.

I'm adding this method to ConstantRange rather than KnownBits (which
would have been a bit nicer API wise) to avoid creating a dependency
from Support to IR, where ConstantRange lives.

Differential Revision: https://reviews.llvm.org/D59475

llvm-svn: 356339

1 files changed, 8 insertions, 11 deletions

diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 9a87667827a..f0c02eec4e2 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -4077,13 +4077,6 @@ static OverflowResult mapOverflowResult(ConstantRange::OverflowResult OR) {
   llvm_unreachable("Unknown OverflowResult");
 }
 
-static ConstantRange constantRangeFromKnownBits(const KnownBits &Known) {
-  if (Known.isUnknown())
-    return ConstantRange(Known.getBitWidth(), /* full */ true);
-
-  return ConstantRange(Known.One, ~Known.Zero + 1);
-}
-
 OverflowResult llvm::computeOverflowForUnsignedAdd(
     const Value *LHS, const Value *RHS, const DataLayout &DL,
     AssumptionCache *AC, const Instruction *CxtI, const DominatorTree *DT,
@@ -4092,8 +4085,10 @@ OverflowResult llvm::computeOverflowForUnsignedAdd(
                                         nullptr, UseInstrInfo);
   KnownBits RHSKnown = computeKnownBits(RHS, DL, /*Depth=*/0, AC, CxtI, DT,
                                         nullptr, UseInstrInfo);
-  ConstantRange LHSRange = constantRangeFromKnownBits(LHSKnown);
-  ConstantRange RHSRange = constantRangeFromKnownBits(RHSKnown);
+  ConstantRange LHSRange =
+      ConstantRange::fromKnownBits(LHSKnown, /*signed*/ false);
+  ConstantRange RHSRange =
+      ConstantRange::fromKnownBits(RHSKnown, /*signed*/ false);
   return mapOverflowResult(LHSRange.unsignedAddMayOverflow(RHSRange));
 }
 
@@ -4208,8 +4203,10 @@ OverflowResult llvm::computeOverflowForUnsignedSub(const Value *LHS,
                                                    const DominatorTree *DT) {
   KnownBits LHSKnown = computeKnownBits(LHS, DL, /*Depth=*/0, AC, CxtI, DT);
   KnownBits RHSKnown = computeKnownBits(RHS, DL, /*Depth=*/0, AC, CxtI, DT);
-  ConstantRange LHSRange = constantRangeFromKnownBits(LHSKnown);
-  ConstantRange RHSRange = constantRangeFromKnownBits(RHSKnown);
+  ConstantRange LHSRange =
+      ConstantRange::fromKnownBits(LHSKnown, /*signed*/ false);
+  ConstantRange RHSRange =
+      ConstantRange::fromKnownBits(RHSKnown, /*signed*/ false);
   return mapOverflowResult(LHSRange.unsignedSubMayOverflow(RHSRange));
 }