[AArch64][SME] Don't use OBSCURE_COPY to avoid rematerialization.

This is intended to be a non-functional change. This patch removes
OBSCURE_COPY in favour of using `forceDisableTriviallyReMaterializable`.

Reviewed By: paulwalker-arm

Differential Revision: https://reviews.llvm.org/D159194

Author: sdesmalen-arm

llvm/lib/Target/AArch64/AArch64ExpandPseudoInsts.cpp

@@ -1515,17 +1515,6 @@ bool AArch64ExpandPseudo::expandMI(MachineBasicBlock &MBB,
        NextMBBI = MBB.end(); // The NextMBBI iterator is invalidated.
      return true;
    }
-   case AArch64::OBSCURE_COPY: {
-     if (MI.getOperand(0).getReg() != MI.getOperand(1).getReg()) {
-       BuildMI(MBB, MBBI, MI.getDebugLoc(), TII->get(AArch64::ORRXrs))
-           .add(MI.getOperand(0))
-           .addReg(AArch64::XZR)
-           .add(MI.getOperand(1))
-           .addImm(0);
-     }
-     MI.eraseFromParent();
-     return true;
-   }
    case AArch64::LD1B_2Z_IMM_PSEUDO:
      return expandMultiVecPseudo(
          MBB, MBBI, AArch64::ZPR2RegClass, AArch64::ZPR2StridedRegClass,

llvm/lib/Target/AArch64/AArch64ISelLowering.cpp

@@ -2303,7 +2303,6 @@ const char *AArch64TargetLowering::getTargetNodeName(unsigned Opcode) const {
   switch ((AArch64ISD::NodeType)Opcode) {
   case AArch64ISD::FIRST_NUMBER:
     break;
-    MAKE_CASE(AArch64ISD::OBSCURE_COPY)
     MAKE_CASE(AArch64ISD::SMSTART)
     MAKE_CASE(AArch64ISD::SMSTOP)
     MAKE_CASE(AArch64ISD::RESTORE_ZA)
@@ -7510,11 +7509,6 @@ AArch64TargetLowering::LowerCall(CallLoweringInfo &CLI,
           return ArgReg.Reg == VA.getLocReg();
         });
       } else {
-        // Add an extra level of indirection for streaming mode changes by
-        // using a pseudo copy node that cannot be rematerialised between a
-        // smstart/smstop and the call by the simple register coalescer.
-        if (RequiresSMChange && isa<FrameIndexSDNode>(Arg))
-          Arg = DAG.getNode(AArch64ISD::OBSCURE_COPY, DL, MVT::i64, Arg);
         RegsToPass.emplace_back(VA.getLocReg(), Arg);
         RegsUsed.insert(VA.getLocReg());
         const TargetOptions &Options = DAG.getTarget().Options;

llvm/lib/Target/AArch64/AArch64ISelLowering.h

@@ -58,13 +58,6 @@ enum NodeType : unsigned {
 
   CALL_BTI, // Function call followed by a BTI instruction.
 
-  // Essentially like a normal COPY that works on GPRs, but cannot be
-  // rematerialised by passes like the simple register coalescer. It's
-  // required for SME when lowering calls because we cannot allow frame
-  // index calculations using addvl to slip in between the smstart/smstop
-  // and the bl instruction. The scalable vector length may change across
-  // the smstart/smstop boundary.
-  OBSCURE_COPY,
   SMSTART,
   SMSTOP,
   RESTORE_ZA,

llvm/lib/Target/AArch64/AArch64InstrInfo.cpp

@@ -8538,7 +8538,11 @@ bool AArch64InstrInfo::isReallyTriviallyReMaterializable(
     // scalable values, such as 'pfalse' or 'ptrue', which result in different
     // results when the runtime vector length is different.
     const MachineRegisterInfo &MRI = MF.getRegInfo();
-    if (any_of(MI.operands(), [&MRI](const MachineOperand &MO) {
+    const MachineFrameInfo &MFI = MF.getFrameInfo();
+    if (any_of(MI.operands(), [&MRI, &MFI](const MachineOperand &MO) {
+          if (MO.isFI() &&
+              MFI.getStackID(MO.getIndex()) == TargetStackID::ScalableVector)
+            return true;
           if (!MO.isReg())
             return false;
 

llvm/lib/Target/AArch64/AArch64SMEInstrInfo.td

@@ -23,8 +23,6 @@ def AArch64_restore_za : SDNode<"AArch64ISD::RESTORE_ZA", SDTypeProfile<0, 3,
                              [SDNPHasChain, SDNPSideEffect, SDNPVariadic,
                               SDNPOptInGlue]>;
 
-def AArch64ObscureCopy : SDNode<"AArch64ISD::OBSCURE_COPY", SDTypeProfile<1, 1, []>, []>;
-
 //===----------------------------------------------------------------------===//
 // Instruction naming conventions.
 //===----------------------------------------------------------------------===//
@@ -185,10 +183,6 @@ def : Pat<(int_aarch64_sme_set_tpidr2 i64:$val),
           (MSR 0xde85, GPR64:$val)>;
 def : Pat<(i64 (int_aarch64_sme_get_tpidr2)),
           (MRS 0xde85)>;
-
-def OBSCURE_COPY : Pseudo<(outs GPR64:$dst), (ins GPR64:$idx), []>, Sched<[]> { }
-def : Pat<(i64 (AArch64ObscureCopy (i64 GPR64:$idx))),
-          (OBSCURE_COPY GPR64:$idx)>;
 } // End let Predicates = [HasSME]
 
 // Pseudo to match to smstart/smstop. This expands: