[AArch64][NEON] Match (or (and -a b) (and (a+1) b)) => bit select

[bsmith]

Summary

With this patch vbslq_f32(vnegq_s32(a), b, c) lowers to a BIT instruction.

Co-authored-by: Paul Walker <[e-mail]>

[dmgreen]

llvm/lib/Target/AArch64/AArch64ISelLowering.cpp

12577

What do the N= and O= signify?

llvm/test/CodeGen/AArch64/neon-bitselect.ll

12

You missed one :-)

[bsmith]

• Add missing test
• Tidy up comment

[joechrisellis]

llvm/lib/Target/AArch64/AArch64ISelLowering.cpp

12581–12597

Small suggestion -- it might be possible to get rid of some duplicate code here by doing something like:

if (O0.getOpcode() == ISD::SUB)
    std::swap(O0, O1);

if (O1.getOpcode() != ISD::ADD)
    continue;

// if we get here, O0 is guaranteed to be the sub, and O1 the add
...

If this works, I _think_ it might make things clearer. But I don't know for sure. If it starts to look uglier then I have no problem with it as-is. :)

llvm/test/CodeGen/AArch64/neon-bitselect.ll

3

Can we add this as an attribute instead? 😄

attributes #0 = { "target-features"="+neon" }

[bsmith]

llvm/lib/Target/AArch64/AArch64ISelLowering.cpp

12581–12597

To be honest I think something like this is just going to end up being more confusing, for the sake of saving a couple of duplicated lines, I really don't think it's worth it. Also note that your example doesn't work since the second check isn't correct in the case the operands have been swapped.

[joechrisellis]

llvm/lib/Target/AArch64/AArch64ISelLowering.cpp

12581–12597

You're right! It should have been something like:

if (O0.getOpcode() != ISD::SUB)
    std::swap(O0, O1);

if (O0.getOpcode() != ISD::SUB || O1.getOpcode() != ISD::ADD)
    continue;

// if we get here, O0 is guaranteed to be the sub, and O1 the add
...

... either way, you are right; N0 and N1 make this a bit more awkward than I had anticipated. ACK. 🙂

[bsmith]

• Use attribute in tests in favour of -mattr on run line

[dmgreen]

I would have gone the other way, making the mtriple and mattr both command line args. LGTM either way though.

llvm/lib/Target/AArch64/AArch64ISelLowering.cpp

static SDValue tryCombineToBSL(SDNode *N,
   SDValue N0 = N->getOperand(0);
   if (N0.getOpcode() != ISD::AND)
     return SDValue();
 
   SDValue N1 = N->getOperand(1);
   if (N1.getOpcode() != ISD::AND)
     return SDValue();
 
+  // InstCombine does (not (neg a)) => (add a -1).
+  // Try: (or (and (neg a) b) (and (add a -1) c)) => (bsl (neg a) b c)
+  // Loop over all combinations of AND operands.
+  for (int i = 1; i >= 0; --i) {
+    for (int j = 1; j >= 0; --j) {
+      SDValue O0 = N0->getOperand(i);
+      SDValue O1 = N1->getOperand(j);
+      SDValue Sub, Add, SubSibling, AddSibling;
+
+      // Find a SUB and an ADD operand, one from each AND.
+      if (O0.getOpcode() == ISD::SUB && O1.getOpcode() == ISD::ADD) {
+        Sub = O0;
+        Add = O1;
+        SubSibling = N0->getOperand(1 - i);
+        AddSibling = N1->getOperand(1 - j);
+      } else if (O0.getOpcode() == ISD::ADD && O1.getOpcode() == ISD::SUB) {
+        Add = O0;
+        Sub = O1;
+        AddSibling = N0->getOperand(1 - i);
+        SubSibling = N1->getOperand(1 - j);
+      } else
+        continue;
+
+      if (!ISD::isBuildVectorAllZeros(Sub.getOperand(0).getNode()))
+        continue;
+
+      // Constant ones is always righthand operand of the Add.
+      if (!ISD::isBuildVectorAllOnes(Add.getOperand(1).getNode()))
+        continue;
+
+      if (Sub.getOperand(1) != Add.getOperand(0))
+        continue;
+
+      return DAG.getNode(AArch64ISD::BSP, DL, VT, Sub, SubSibling, AddSibling);
+    }
+  }
+
+  // (or (and a b) (and (not a) c)) => (bsl a b c)
   // We only have to look for constant vectors here since the general, variable
   // case can be handled in TableGen.
   unsigned Bits = VT.getScalarSizeInBits();
   uint64_t BitMask = Bits == 64 ? -1ULL : ((1ULL << Bits) - 1);
   for (int i = 1; i >= 0; --i)
     for (int j = 1; j >= 0; --j) {
       BuildVectorSDNode *BVN0 = dyn_cast<BuildVectorSDNode>(N0->getOperand(i));
       BuildVectorSDNode *BVN1 = dyn_cast<BuildVectorSDNode>(N1->getOperand(j));

llvm/test/CodeGen/AArch64/neon-bitselect.ll

+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc < %s | FileCheck %s
+
+target triple = "aarch64"
+
+; Check that an expanded vbsl(vneg(pre_cond), left, right) lowers to a VBSL
+; during ISEL.
+;
+; Subtly different from a plain vector bit select: operand representing the
+; condition has been negated (-v, not to be confused with bitwise_not(v)).
+
+; Each vbsl_neg_cond_xxxx tests one of the 16 permutations of the operands.
+
+define <4 x i32> @vbsl_neg_cond_0000(<4 x i32> %pre_cond, <4 x i32> %left, <4 x i32> %right) #0 {
+; CHECK-LABEL: vbsl_neg_cond_0000:
+; CHECK:       // %bb.0:
+; CHECK-NEXT:    neg v0.4s, v0.4s
+; CHECK-NEXT:    bsl v0.16b, v1.16b, v2.16b
+; CHECK-NEXT:    ret
+  %neg_cond = sub <4 x i32> zeroinitializer, %pre_cond
+  %min_cond = add <4 x i32> %pre_cond, <i32 -1, i32 -1, i32 -1, i32 -1>
+  %left_bits_0 = and <4 x i32> %neg_cond, %left
+  %right_bits_0 = and <4 x i32> %min_cond, %right
+  %bsl0000 = or <4 x i32> %right_bits_0, %left_bits_0
+  ret <4 x i32> %bsl0000
+}
+
+define <4 x i32> @vbsl_neg_cond_0001(<4 x i32> %pre_cond, <4 x i32> %left, <4 x i32> %right) #0 {
+; CHECK-LABEL: vbsl_neg_cond_0001:
+; CHECK:       // %bb.0:
+; CHECK-NEXT:    neg v0.4s, v0.4s
+; CHECK-NEXT:    bsl v0.16b, v1.16b, v2.16b
+; CHECK-NEXT:    ret
+  %neg_cond = sub <4 x i32> zeroinitializer, %pre_cond
+  %min_cond = add <4 x i32> %pre_cond, <i32 -1, i32 -1, i32 -1, i32 -1>
+  %left_bits_1 = and <4 x i32> %left, %neg_cond
+  %right_bits_0 = and <4 x i32> %min_cond, %right
+  %bsl0001 = or <4 x i32> %right_bits_0, %left_bits_1
+  ret <4 x i32> %bsl0001
+}
+
+define <4 x i32> @vbsl_neg_cond_0010(<4 x i32> %pre_cond, <4 x i32> %left, <4 x i32> %right) #0 {
+; CHECK-LABEL: vbsl_neg_cond_0010:
+; CHECK:       // %bb.0:
+; CHECK-NEXT:    neg v0.4s, v0.4s
+; CHECK-NEXT:    bsl v0.16b, v1.16b, v2.16b
+; CHECK-NEXT:    ret
+  %neg_cond = sub <4 x i32> zeroinitializer, %pre_cond
+  %min_cond = add <4 x i32> %pre_cond, <i32 -1, i32 -1, i32 -1, i32 -1>
+  %left_bits_0 = and <4 x i32> %neg_cond, %left
+  %right_bits_1 = and <4 x i32> %right, %min_cond
+  %bsl0010 = or <4 x i32> %right_bits_1, %left_bits_0
+  ret <4 x i32> %bsl0010
+}
+
+define <4 x i32> @vbsl_neg_cond_0011(<4 x i32> %pre_cond, <4 x i32> %left, <4 x i32> %right) #0 {
+; CHECK-LABEL: vbsl_neg_cond_0011:
+; CHECK:       // %bb.0:
+; CHECK-NEXT:    neg v0.4s, v0.4s
+; CHECK-NEXT:    bsl v0.16b, v1.16b, v2.16b
+; CHECK-NEXT:    ret
+  %neg_cond = sub <4 x i32> zeroinitializer, %pre_cond
+  %min_cond = add <4 x i32> %pre_cond, <i32 -1, i32 -1, i32 -1, i32 -1>
+  %left_bits_1 = and <4 x i32> %left, %neg_cond
+  %right_bits_1 = and <4 x i32> %right, %min_cond
+  %bsl0011 = or <4 x i32> %right_bits_1, %left_bits_1
+  ret <4 x i32> %bsl0011
+}
+
+define <4 x i32> @vbsl_neg_cond_0100(<4 x i32> %pre_cond, <4 x i32> %left, <4 x i32> %right) #0 {
+; CHECK-LABEL: vbsl_neg_cond_0100:
+; CHECK:       // %bb.0:
+; CHECK-NEXT:    neg v0.4s, v0.4s
+; CHECK-NEXT:    bsl v0.16b, v1.16b, v2.16b
+; CHECK-NEXT:    ret
+  %neg_cond = sub <4 x i32> zeroinitializer, %pre_cond
+  %min_cond = add <4 x i32> %pre_cond, <i32 -1, i32 -1, i32 -1, i32 -1>
+  %left_bits_0 = and <4 x i32> %neg_cond, %left
+  %right_bits_0 = and <4 x i32> %min_cond, %right
+  %bsl0100 = or <4 x i32> %left_bits_0, %right_bits_0
+  ret <4 x i32> %bsl0100
+}
+
+define <4 x i32> @vbsl_neg_cond_0101(<4 x i32> %pre_cond, <4 x i32> %left, <4 x i32> %right) #0 {
+; CHECK-LABEL: vbsl_neg_cond_0101:
+; CHECK:       // %bb.0:
+; CHECK-NEXT:    neg v0.4s, v0.4s
+; CHECK-NEXT:    bsl v0.16b, v1.16b, v2.16b
+; CHECK-NEXT:    ret
+  %neg_cond = sub <4 x i32> zeroinitializer, %pre_cond
+  %min_cond = add <4 x i32> %pre_cond, <i32 -1, i32 -1, i32 -1, i32 -1>
+  %left_bits_0 = and <4 x i32> %neg_cond, %left
+  %right_bits_1 = and <4 x i32> %right, %min_cond
+  %bsl0101 = or <4 x i32> %left_bits_0, %right_bits_1
+  ret <4 x i32> %bsl0101
+}
+
+define <4 x i32> @vbsl_neg_cond_0110(<4 x i32> %pre_cond, <4 x i32> %left, <4 x i32> %right) #0 {
+; CHECK-LABEL: vbsl_neg_cond_0110:
+; CHECK:       // %bb.0:
+; CHECK-NEXT:    neg v0.4s, v0.4s
+; CHECK-NEXT:    bsl v0.16b, v1.16b, v2.16b
+; CHECK-NEXT:    ret
+  %neg_cond = sub <4 x i32> zeroinitializer, %pre_cond
+  %min_cond = add <4 x i32> %pre_cond, <i32 -1, i32 -1, i32 -1, i32 -1>
+  %left_bits_1 = and <4 x i32> %left, %neg_cond
+  %right_bits_0 = and <4 x i32> %min_cond, %right
+  %bsl0110 = or <4 x i32> %left_bits_1, %right_bits_0
+  ret <4 x i32> %bsl0110
+}
+
+define <4 x i32> @vbsl_neg_cond_0111(<4 x i32> %pre_cond, <4 x i32> %left, <4 x i32> %right) #0 {
+; CHECK-LABEL: vbsl_neg_cond_0111:
+; CHECK:       // %bb.0:
+; CHECK-NEXT:    neg v0.4s, v0.4s
+; CHECK-NEXT:    bsl v0.16b, v1.16b, v2.16b
+; CHECK-NEXT:    ret
+  %neg_cond = sub <4 x i32> zeroinitializer, %pre_cond
+  %min_cond = add <4 x i32> %pre_cond, <i32 -1, i32 -1, i32 -1, i32 -1>
+  %left_bits_1 = and <4 x i32> %left, %neg_cond
+  %right_bits_1 = and <4 x i32> %right, %min_cond
+  %bsl0111 = or <4 x i32> %left_bits_1, %right_bits_1
+  ret <4 x i32> %bsl0111
+}
+
+define <4 x i32> @vbsl_neg_cond_1000(<4 x i32> %pre_cond, <4 x i32> %left, <4 x i32> %right) #0 {
+; CHECK-LABEL: vbsl_neg_cond_1000:
+; CHECK:       // %bb.0:
+; CHECK-NEXT:    neg v0.4s, v0.4s
+; CHECK-NEXT:    bsl v0.16b, v2.16b, v1.16b
+; CHECK-NEXT:    ret
+  %neg_cond = sub <4 x i32> zeroinitializer, %pre_cond
+  %min_cond = add <4 x i32> %pre_cond, <i32 -1, i32 -1, i32 -1, i32 -1>
+  %flip_cond_left_bits_0 = and <4 x i32> %min_cond, %left
+  %flip_cond_right_bits_0 = and <4 x i32> %neg_cond, %right
+  %bsl1000 = or <4 x i32> %flip_cond_right_bits_0, %flip_cond_left_bits_0
+  ret <4 x i32> %bsl1000
+}
+
+define <4 x i32> @vbsl_neg_cond_1001(<4 x i32> %pre_cond, <4 x i32> %left, <4 x i32> %right) #0 {
+; CHECK-LABEL: vbsl_neg_cond_1001:
+; CHECK:       // %bb.0:
+; CHECK-NEXT:    neg v0.4s, v0.4s
+; CHECK-NEXT:    bsl v0.16b, v2.16b, v1.16b
+; CHECK-NEXT:    ret
+  %neg_cond = sub <4 x i32> zeroinitializer, %pre_cond
+  %min_cond = add <4 x i32> %pre_cond, <i32 -1, i32 -1, i32 -1, i32 -1>
+  %flip_cond_left_bits_1 = and <4 x i32> %left, %min_cond
+  %flip_cond_right_bits_0 = and <4 x i32> %neg_cond, %right
+  %bsl1001 = or <4 x i32> %flip_cond_right_bits_0, %flip_cond_left_bits_1
+  ret <4 x i32> %bsl1001
+}
+
+define <4 x i32> @vbsl_neg_cond_1010(<4 x i32> %pre_cond, <4 x i32> %left, <4 x i32> %right) #0 {
+; CHECK-LABEL: vbsl_neg_cond_1010:
+; CHECK:       // %bb.0:
+; CHECK-NEXT:    neg v0.4s, v0.4s
+; CHECK-NEXT:    bsl v0.16b, v2.16b, v1.16b
+; CHECK-NEXT:    ret
+  %neg_cond = sub <4 x i32> zeroinitializer, %pre_cond
+  %min_cond = add <4 x i32> %pre_cond, <i32 -1, i32 -1, i32 -1, i32 -1>
+  %flip_cond_left_bits_0 = and <4 x i32> %min_cond, %left
+  %flip_cond_right_bits_1 = and <4 x i32> %right, %neg_cond
+  %bsl1010 = or <4 x i32> %flip_cond_right_bits_1, %flip_cond_left_bits_0
+  ret <4 x i32> %bsl1010
+}
+
+define <4 x i32> @vbsl_neg_cond_1011(<4 x i32> %pre_cond, <4 x i32> %left, <4 x i32> %right) #0 {
+; CHECK-LABEL: vbsl_neg_cond_1011:
+; CHECK:       // %bb.0:
+; CHECK-NEXT:    neg v0.4s, v0.4s
+; CHECK-NEXT:    bsl v0.16b, v2.16b, v1.16b
+; CHECK-NEXT:    ret
+  %neg_cond = sub <4 x i32> zeroinitializer, %pre_cond
+  %min_cond = add <4 x i32> %pre_cond, <i32 -1, i32 -1, i32 -1, i32 -1>
+  %flip_cond_left_bits_1 = and <4 x i32> %left, %min_cond
+  %flip_cond_right_bits_1 = and <4 x i32> %right, %neg_cond
+  %bsl1011 = or <4 x i32> %flip_cond_right_bits_1, %flip_cond_left_bits_1
+  ret <4 x i32> %bsl1011
+}
+
+define <4 x i32> @vbsl_neg_cond_1100(<4 x i32> %pre_cond, <4 x i32> %left, <4 x i32> %right) #0 {
+; CHECK-LABEL: vbsl_neg_cond_1100:
+; CHECK:       // %bb.0:
+; CHECK-NEXT:    neg v0.4s, v0.4s
+; CHECK-NEXT:    bsl v0.16b, v2.16b, v1.16b
+; CHECK-NEXT:    ret
+  %neg_cond = sub <4 x i32> zeroinitializer, %pre_cond
+  %min_cond = add <4 x i32> %pre_cond, <i32 -1, i32 -1, i32 -1, i32 -1>
+  %flip_cond_left_bits_0 = and <4 x i32> %min_cond, %left
+  %flip_cond_right_bits_0 = and <4 x i32> %neg_cond, %right
+  %bsl1100 = or <4 x i32> %flip_cond_left_bits_0, %flip_cond_right_bits_0
+  ret <4 x i32> %bsl1100
+}
+
+define <4 x i32> @vbsl_neg_cond_1101(<4 x i32> %pre_cond, <4 x i32> %left, <4 x i32> %right) #0 {
+; CHECK-LABEL: vbsl_neg_cond_1101:
+; CHECK:       // %bb.0:
+; CHECK-NEXT:    neg v0.4s, v0.4s
+; CHECK-NEXT:    bsl v0.16b, v2.16b, v1.16b
+; CHECK-NEXT:    ret
+  %neg_cond = sub <4 x i32> zeroinitializer, %pre_cond
+  %min_cond = add <4 x i32> %pre_cond, <i32 -1, i32 -1, i32 -1, i32 -1>
+  %flip_cond_left_bits_0 = and <4 x i32> %min_cond, %left
+  %flip_cond_right_bits_1 = and <4 x i32> %right, %neg_cond
+  %bsl1101 = or <4 x i32> %flip_cond_left_bits_0, %flip_cond_right_bits_1
+  ret <4 x i32> %bsl1101
+}
+
+define <4 x i32> @vbsl_neg_cond_1110(<4 x i32> %pre_cond, <4 x i32> %left, <4 x i32> %right) #0 {
+; CHECK-LABEL: vbsl_neg_cond_1110:
+; CHECK:       // %bb.0:
+; CHECK-NEXT:    neg v0.4s, v0.4s
+; CHECK-NEXT:    bsl v0.16b, v2.16b, v1.16b
+; CHECK-NEXT:    ret
+  %neg_cond = sub <4 x i32> zeroinitializer, %pre_cond
+  %min_cond = add <4 x i32> %pre_cond, <i32 -1, i32 -1, i32 -1, i32 -1>
+  %flip_cond_left_bits_1 = and <4 x i32> %left, %min_cond
+  %flip_cond_right_bits_0 = and <4 x i32> %neg_cond, %right
+  %bsl1110 = or <4 x i32> %flip_cond_left_bits_1, %flip_cond_right_bits_0
+  ret <4 x i32> %bsl1110
+}
+
+define <4 x i32> @vbsl_neg_cond_1111(<4 x i32> %pre_cond, <4 x i32> %left, <4 x i32> %right) #0 {
+; CHECK-LABEL: vbsl_neg_cond_1111:
+; CHECK:       // %bb.0:
+; CHECK-NEXT:    neg v0.4s, v0.4s
+; CHECK-NEXT:    bsl v0.16b, v2.16b, v1.16b
+; CHECK-NEXT:    ret
+  %neg_cond = sub <4 x i32> zeroinitializer, %pre_cond
+  %min_cond = add <4 x i32> %pre_cond, <i32 -1, i32 -1, i32 -1, i32 -1>
+  %flip_cond_left_bits_1 = and <4 x i32> %left, %min_cond
+  %flip_cond_right_bits_1 = and <4 x i32> %right, %neg_cond
+  %bsl1111 = or <4 x i32> %flip_cond_left_bits_1, %flip_cond_right_bits_1
+  ret <4 x i32> %bsl1111
+}
+
+attributes #0 = { "target-features"="+neon" }