Allows scalable vectors in ComputeNumSignBits and isKnownNonNull

[reames]

Summary

This is a follow up to D136470 which extends the same scheme used there to ComputeNumSignBits and isKnownNonNull. As a reminder, for scalable vectors we track a single bit which is implicitly broadcast to all lanes. We do not know how many lanes there are statically, and thus have to be conservative along paths which require exact sizes.

(Note: This patch is pending rebase over a couple new tests to demonstrate the change better - expect that Monday.)

[reames]

Tests needed.

And it looks like I missed a required bailout in IntToPtr and PtrToInt handling. (They both expect fixed sizes.) This also needs test coverage.

[reames]

Rebase over tests, and be conservative about inttoptr or ptrtoint involving scalable types. These require a bit of care - and tests - to handle, so simply exclude them from the initial patch.

[craig.topper]

LGTM

[paulwalker-arm]

llvm/lib/Analysis/ValueTracking.cpp

2567

Minor quibble but this is implied by the following !isa<ScalableVectorType>(I->getType()) check.

[reames]

llvm/lib/Analysis/ValueTracking.cpp

2567

I agree. This isn't checked by castIsValid which is what I'd expected, but the verifier does directly compare the element counts which should fail if only one is scalable. Will remove in a follow up commit.

[reames]

llvm/lib/Analysis/ValueTracking.cpp

2567

Done. 9472a81

llvm/lib/Analysis/ValueTracking.cpp

return ::MaskedValueIsZero(
       V, Mask, Depth, Query(DL, AC, safeCxtI(V, CxtI), DT, UseInstrInfo));
 }
 
 static unsigned ComputeNumSignBits(const Value *V, const APInt &DemandedElts,
                                    unsigned Depth, const Query &Q);
 
 static unsigned ComputeNumSignBits(const Value *V, unsigned Depth,
                                    const Query &Q) {
-  // FIXME: We currently have no way to represent the DemandedElts of a scalable
-  // vector
-  if (isa<ScalableVectorType>(V->getType()))
-    return 1;
-
   auto *FVTy = dyn_cast<FixedVectorType>(V->getType());
   APInt DemandedElts =
       FVTy ? APInt::getAllOnes(FVTy->getNumElements()) : APInt(1, 1);
   return ComputeNumSignBits(V, DemandedElts, Depth, Q);
 }
 
 unsigned llvm::ComputeNumSignBits(const Value *V, const DataLayout &DL,
                                   unsigned Depth, AssumptionCache *AC,

 /// Return true if the given value is known to be non-zero when defined. For
 /// vectors, return true if every demanded element is known to be non-zero when
 /// defined. For pointers, if the context instruction and dominator tree are
 /// specified, perform context-sensitive analysis and return true if the
 /// pointer couldn't possibly be null at the specified instruction.
 /// Supports values with integer or pointer type and vectors of integers.
 bool isKnownNonZero(const Value *V, const APInt &DemandedElts, unsigned Depth,
                     const Query &Q) {
-  // FIXME: We currently have no way to represent the DemandedElts of a scalable
-  // vector
-  if (isa<ScalableVectorType>(V->getType()))
-    return false;
 
 #ifndef NDEBUG
   Type *Ty = V->getType();
   assert(Depth <= MaxAnalysisRecursionDepth && "Limit Search Depth");
 
   if (auto *FVTy = dyn_cast<FixedVectorType>(Ty)) {
     assert(
         FVTy->getNumElements() == DemandedElts.getBitWidth() &&
#endif
   case Instruction::BitCast:
     if (I->getType()->isPointerTy())
       return isKnownNonZero(I->getOperand(0), Depth, Q);
     break;
   case Instruction::IntToPtr:
     // Note that we have to take special care to avoid looking through
     // truncating casts, e.g., int2ptr/ptr2int with appropriate sizes, as well
     // as casts that can alter the value, e.g., AddrSpaceCasts.
     if (Q.DL.getTypeSizeInBits(I->getOperand(0)->getType()).getFixedSize() <=
         Q.DL.getTypeSizeInBits(I->getType()).getFixedSize())
       return isKnownNonZero(I->getOperand(0), Depth, Q);
     break;
   case Instruction::PtrToInt:
     // Similar to int2ptr above, we can look through ptr2int here if the cast
     // is a no-op or an extend and not a truncate.
     if (Q.DL.getTypeSizeInBits(I->getOperand(0)->getType()).getFixedSize() <=
         Q.DL.getTypeSizeInBits(I->getType()).getFixedSize())
#endif
   }
 
   KnownBits Known(BitWidth);
   computeKnownBits(V, DemandedElts, Known, Depth, Q);
   return Known.One != 0;
 }
 
 bool isKnownNonZero(const Value* V, unsigned Depth, const Query& Q) {
-  // FIXME: We currently have no way to represent the DemandedElts of a scalable
-  // vector
-  if (isa<ScalableVectorType>(V->getType()))
-    return false;
-
   auto *FVTy = dyn_cast<FixedVectorType>(V->getType());
   APInt DemandedElts =
       FVTy ? APInt::getAllOnes(FVTy->getNumElements()) : APInt(1, 1);
   return isKnownNonZero(V, DemandedElts, Depth, Q);
 }
 
 /// If the pair of operators are the same invertible function, return the
 /// the operands of the function corresponding to each input. Otherwise,

 /// after an "ashr X, 2", we know that the top 3 bits are all equal to each
 /// other, so we return 3. For vectors, return the number of sign bits for the
 /// vector element with the minimum number of known sign bits of the demanded
 /// elements in the vector specified by DemandedElts.
 static unsigned ComputeNumSignBitsImpl(const Value *V,
                                        const APInt &DemandedElts,
                                        unsigned Depth, const Query &Q) {
   Type *Ty = V->getType();
-
-  // FIXME: We currently have no way to represent the DemandedElts of a scalable
-  // vector
-  if (isa<ScalableVectorType>(Ty))
-    return 1;
-
 #ifndef NDEBUG
   assert(Depth <= MaxAnalysisRecursionDepth && "Limit Search Depth");
 
   if (auto *FVTy = dyn_cast<FixedVectorType>(Ty)) {
     assert(
         FVTy->getNumElements() == DemandedElts.getBitWidth() &&
         "DemandedElt width should equal the fixed vector number of elements");
   } else {

llvm/test/Transforms/InstCombine/logical-select.ll

;
   %t11 = and <2 x i64> %nott9, %c
   %t12 = and <2 x i64> %t9, %d
   %r = or <2 x i64> %t11, %t12
   ret <2 x i64> %r
 }
 
 define <vscale x 2 x i64> @bitcast_vec_cond_scalable(<vscale x 16 x i1> %cond, <vscale x 2 x i64> %c, <vscale x 2 x i64> %d) {
 ; CHECK-LABEL: @bitcast_vec_cond_scalable(
-; CHECK-NEXT:    [[S:%.*]] = sext <vscale x 16 x i1> [[COND:%.*]] to <vscale x 16 x i8>
-; CHECK-NEXT:    [[T9:%.*]] = bitcast <vscale x 16 x i8> [[S]] to <vscale x 2 x i64>
-; CHECK-NEXT:    [[NOTT9:%.*]] = xor <vscale x 2 x i64> [[T9]], shufflevector (<vscale x 2 x i64> insertelement (<vscale x 2 x i64> poison, i64 -1, i32 0), <vscale x 2 x i64> poison, <vscale x 2 x i32> zeroinitializer)
-; CHECK-NEXT:    [[T11:%.*]] = and <vscale x 2 x i64> [[NOTT9]], [[C:%.*]]
-; CHECK-NEXT:    [[T12:%.*]] = and <vscale x 2 x i64> [[T9]], [[D:%.*]]
-; CHECK-NEXT:    [[R:%.*]] = or <vscale x 2 x i64> [[T11]], [[T12]]
-; CHECK-NEXT:    ret <vscale x 2 x i64> [[R]]
+; CHECK-NEXT:    [[TMP1:%.*]] = bitcast <vscale x 2 x i64> [[D:%.*]] to <vscale x 16 x i8>
+; CHECK-NEXT:    [[TMP2:%.*]] = bitcast <vscale x 2 x i64> [[C:%.*]] to <vscale x 16 x i8>
+; CHECK-NEXT:    [[TMP3:%.*]] = select <vscale x 16 x i1> [[COND:%.*]], <vscale x 16 x i8> [[TMP1]], <vscale x 16 x i8> [[TMP2]]
+; CHECK-NEXT:    [[TMP4:%.*]] = bitcast <vscale x 16 x i8> [[TMP3]] to <vscale x 2 x i64>
+; CHECK-NEXT:    ret <vscale x 2 x i64> [[TMP4]]
 ;
   %s = sext <vscale x 16 x i1> %cond to <vscale x 16 x i8>
   %t9 = bitcast <vscale x 16 x i8> %s to <vscale x 2 x i64>
   %nott9 = xor <vscale x 2 x i64> %t9, shufflevector (<vscale x 2 x i64> insertelement (<vscale x 2 x i64> poison, i64 -1, i32 0), <vscale x 2 x i64> poison, <vscale x 2 x i32> zeroinitializer)
   %t11 = and <vscale x 2 x i64> %nott9, %c
   %t12 = and <vscale x 2 x i64> %t9, %d
   %r = or <vscale x 2 x i64> %t11, %t12
   ret <vscale x 2 x i64> %r