[ARM][MVE] Tail-predication: use unsigned SCEV ranges for tripcount

Loop tripcount expressions have a positive range, so use unsigned SCEV ranges
for them.

Differential Revision: https://reviews.llvm.org/D87608

diff --git a/llvm/lib/Target/ARM/MVETailPredication.cpp b/llvm/lib/Target/ARM/MVETailPredication.cpp
index b2c15be..987df73 100644 (file)
--- a/llvm/lib/Target/ARM/MVETailPredication.cpp
+++ b/llvm/lib/Target/ARM/MVETailPredication.cpp
@@ -457,13 +457,10 @@ bool MVETailPredication::IsSafeActiveMask(IntrinsicInst *ActiveLaneMask,
   //     upperbound(TC) <= UINT_MAX - VectorWidth
   //
   unsigned SizeInBits = TripCount->getType()->getScalarSizeInBits();
-  auto Diff = APInt(SizeInBits, ~0) - APInt(SizeInBits, VectorWidth);
-  uint64_t MaxMinusVW = Diff.getZExtValue();
-  // FIXME: since ranges can be negative we work with signed ranges here, but
-  // we shouldn't extract the zext'ed values for them.
-  uint64_t UpperboundTC = SE->getSignedRange(TC).getUpper().getZExtValue();
+  auto MaxMinusVW = APInt(SizeInBits, ~0) - APInt(SizeInBits, VectorWidth);
+  APInt UpperboundTC = SE->getUnsignedRangeMax(TC);
 
-  if (UpperboundTC > MaxMinusVW && !ForceTailPredication) {
+  if (UpperboundTC.ugt(MaxMinusVW) && !ForceTailPredication) {
     LLVM_DEBUG(dbgs() << "ARM TP: Overflow possible in tripcount rounding:\n";
                dbgs() << "upperbound(TC) <= UINT_MAX - VectorWidth\n";
                dbgs() << UpperboundTC << " <= " << MaxMinusVW << " == false\n";);
@@ -501,8 +498,8 @@ bool MVETailPredication::IsSafeActiveMask(IntrinsicInst *ActiveLaneMask,
   auto *Ceil = SE->getUDivExpr(ECPlusVWMinus1,
       SE->getSCEV(ConstantInt::get(TripCount->getType(), VectorWidth)));
 
-  ConstantRange RangeCeil = SE->getSignedRange(Ceil) ;
-  ConstantRange RangeTC = SE->getSignedRange(TC) ;
+  ConstantRange RangeCeil = SE->getUnsignedRange(Ceil) ;
+  ConstantRange RangeTC = SE->getUnsignedRange(TC) ;
   if (!RangeTC.isSingleElement()) {
     auto ZeroRange =
         ConstantRange(APInt(TripCount->getType()->getScalarSizeInBits(), 0));