[TableGen][SelectionDAG] Remove the implicit DAG node

The node was introduced in 59c39dc and was intended to allow writing
patterns like this:
`[(set AL, (MULr8 AL, GR8:$src1)), (implicit EFLAGS)]`

However, it does not introduce new functionality because the same
pattern can be equivalently expressed as:
`[(set AL, EFLAGS, (node AL, GR8:$src1))]`

The latter form is also more flexible as it allows reordering output
operands.

In most places uses of `implicit` were redundant -- removing them
didn't change anything in the generated DAG tables. The only three cases
where it did have effect are in X86InstrArithmetic.td and
X86InstrSystem.td -- those were rewritten to use `set` node.

Removing `implicit` from some patterns made them importable by GISel,
hence the change in a test.

Author: s-barannikov

llvm/lib/Target/AArch64/AArch64InstrFormats.td

@@ -2579,8 +2579,7 @@ class BaseAddSubCarry<bit isSub, RegisterClass regtype, string asm,
 class BaseAddSubCarrySetFlags<bit isSub, RegisterClass regtype, string asm,
                               SDNode OpNode>
     : BaseBaseAddSubCarry<isSub, regtype, asm,
-        [(set regtype:$Rd, (OpNode regtype:$Rn, regtype:$Rm, NZCV)),
-         (implicit NZCV)]> {
+        [(set regtype:$Rd, (OpNode regtype:$Rn, regtype:$Rm, NZCV))]> {
   let Defs = [NZCV];
 }
 
@@ -5891,34 +5890,34 @@ multiclass FPComparison<bit signalAllNans, string asm,
                         SDPatternOperator OpNode = null_frag> {
   let Defs = [NZCV] in {
   def Hrr : BaseTwoOperandFPComparison<signalAllNans, FPR16, asm,
-      [(OpNode (f16 FPR16:$Rn), (f16 FPR16:$Rm)), (implicit NZCV)]> {
+      [(OpNode (f16 FPR16:$Rn), (f16 FPR16:$Rm))]> {
     let Inst{23-22} = 0b11;
     let Predicates = [HasFullFP16];
   }
 
   def Hri : BaseOneOperandFPComparison<signalAllNans, FPR16, asm,
-      [(OpNode (f16 FPR16:$Rn), fpimm0), (implicit NZCV)]> {
+      [(OpNode (f16 FPR16:$Rn), fpimm0)]> {
     let Inst{23-22} = 0b11;
     let Predicates = [HasFullFP16];
   }
 
   def Srr : BaseTwoOperandFPComparison<signalAllNans, FPR32, asm,
-      [(OpNode FPR32:$Rn, (f32 FPR32:$Rm)), (implicit NZCV)]> {
+      [(OpNode FPR32:$Rn, (f32 FPR32:$Rm))]> {
     let Inst{23-22} = 0b00;
   }
 
   def Sri : BaseOneOperandFPComparison<signalAllNans, FPR32, asm,
-      [(OpNode (f32 FPR32:$Rn), fpimm0), (implicit NZCV)]> {
+      [(OpNode (f32 FPR32:$Rn), fpimm0)]> {
     let Inst{23-22} = 0b00;
   }
 
   def Drr : BaseTwoOperandFPComparison<signalAllNans, FPR64, asm,
-      [(OpNode FPR64:$Rn, (f64 FPR64:$Rm)), (implicit NZCV)]> {
+      [(OpNode FPR64:$Rn, (f64 FPR64:$Rm))]> {
     let Inst{23-22} = 0b01;
   }
 
   def Dri : BaseOneOperandFPComparison<signalAllNans, FPR64, asm,
-      [(OpNode (f64 FPR64:$Rn), fpimm0), (implicit NZCV)]> {
+      [(OpNode (f64 FPR64:$Rn), fpimm0)]> {
     let Inst{23-22} = 0b01;
   }
   } // Defs = [NZCV]