[NFC][ValueTracking]: Remove redundant computeKnownBits call for LoadInst in isKnownNonZero

[0xdc03]

Summary

For load instructions, computeKnownBits only checks the range metadata.
This check is already present in isKnownNonZero, so there is no need to
fall through to computeKnownBits.

This change gives a speed improvement of 0.18%:
https://llvm-compile-time-tracker.com/compare.php?from=3c6ed559e5274307995586c1499a2c8e4e0276a0&to=78b462d8c4ae079638b728c6446da5999c4ee9f8&stat=instructions:u

[nikic]

llvm/lib/Analysis/ValueTracking.cpp

2451–2452

It would be good to move this check into the load switch case.

[0xdc03]

• Address reviewer comments

llvm/lib/Analysis/ValueTracking.cpp

2451–2452

Done, though I do wonder why this was originally put here. I guess it is a relic from the merge of isKnownNonNull and isKnownNonZero that was never updated.

[0xdc03]

llvm/lib/Analysis/ValueTracking.cpp

2451–2452

For that matter, I guess this could also be moved into the call instruction case?

[goldstein.w.n]

llvm/lib/Analysis/ValueTracking.cpp

2688

"handled above"? "Handled there"?

[nikic]

LGTM

llvm/lib/Analysis/ValueTracking.cpp

2451–2452

Yes, it would make sense to move all the handling here (apart from Argument).

[0xdc03]

llvm/lib/Analysis/ValueTracking.cpp

2451–2452

@goldstein.w.n I was referring to this.

[0xdc03]

• Rebase on main

llvm/lib/Analysis/ValueTracking.cpp

static bool isNonZeroShift(const Operator *I, const APInt &DemandedElts,
   // non-zero then at least one non-zero bit must remain.
   if (InvShiftOp(KnownVal.Zero, NumBits - MaxShift)
           .eq(InvShiftOp(APInt::getAllOnes(NumBits), NumBits - MaxShift)) &&
       isKnownNonZero(I->getOperand(0), DemandedElts, Depth, Q))
     return true;
 
   return false;
 }
 
 static bool isKnownNonZeroFromOperator(const Operator *I,
                                        const APInt &DemandedElts,
                                        unsigned Depth, const SimplifyQuery &Q) {
   unsigned BitWidth = getBitWidth(I->getType()->getScalarType(), Q.DL);
   switch (I->getOpcode()) {
   case Instruction::GetElementPtr:
     if (I->getType()->isPointerTy())
       return isGEPKnownNonNull(cast<GEPOperator>(I), Depth, Q);
     break;
if (const auto *EEI = dyn_cast<ExtractElementInst>(I)) {
         return isKnownNonZero(Vec, DemandedVecElts, Depth, Q);
       }
     }
     break;
   case Instruction::Freeze:
     return isKnownNonZero(I->getOperand(0), Depth, Q) &&
            isGuaranteedNotToBePoison(I->getOperand(0), Q.AC, Q.CxtI, Q.DT,
                                      Depth);
+  case Instruction::Load:
+    // A Load tagged with nonnull metadata is never null.
+    if (Q.IIQ.getMetadata(cast<LoadInst>(I), LLVMContext::MD_nonnull))
+      return true;
+
+    // No need to fall through to computeKnownBits as range metadata is already
+    // handled in isKnownNonZero.
+    return false;
   case Instruction::Call:
     if (auto *II = dyn_cast<IntrinsicInst>(I)) {
       switch (II->getIntrinsicID()) {
       case Intrinsic::sshl_sat:
       case Intrinsic::ushl_sat:
       case Intrinsic::abs:
       case Intrinsic::bitreverse:
       case Intrinsic::bswap:
if (PointerType *PtrTy = dyn_cast<PointerType>(V->getType())) {
     // nonnull argument is assumed never 0.
     if (const Argument *A = dyn_cast<Argument>(V)) {
       if (((A->hasPassPointeeByValueCopyAttr() &&
             !NullPointerIsDefined(A->getParent(), PtrTy->getAddressSpace())) ||
            A->hasNonNullAttr()))
         return true;
     }
 
-    // A Load tagged with nonnull metadata is never null.
-    if (const LoadInst *LI = dyn_cast<LoadInst>(V))
-      if (Q.IIQ.getMetadata(LI, LLVMContext::MD_nonnull))
-        return true;
-
     if (const auto *Call = dyn_cast<CallBase>(V)) {
       if (Call->isReturnNonNull())
         return true;
       if (const auto *RP = getArgumentAliasingToReturnedPointer(Call, true))
         return isKnownNonZero(RP, Depth, Q);
     }
   }