Revert "[AArch64][GlobalISel] Legalize bswap <2 x i16>"

This reverts commit 5cd63e9.

https://bugs.llvm.org/show_bug.cgi?id=51707

The sequence feeding in/out of the rev32/ushr isn't quite right:

 _swap:
         ldr     h0, [x0]
         ldr     h1, [x0, rust-lang#2]
-        mov     v0.h[1], v1.h[0]
+        mov     v0.s[1], v1.s[0]
         rev32   v0.8b, v0.8b
         ushr    v0.2s, v0.2s, rust-lang#16
-        mov     h1, v0.h[1]
+        mov     s1, v0.s[1]
         str     h0, [x0]
         str     h1, [x0, rust-lang#2]
         ret

Author: jroelofs

llvm/lib/Target/AArch64/GISel/AArch64LegalizerInfo.cpp

@@ -110,8 +110,7 @@ AArch64LegalizerInfo::AArch64LegalizerInfo(const AArch64Subtarget &ST)
   getActionDefinitionsBuilder(G_BSWAP)
       .legalFor({s32, s64, v4s32, v2s32, v2s64})
       .widenScalarToNextPow2(0)
-      .clampScalar(0, s32, s64)
-      .customIf(typeIs(0, v2s16)); // custom lower as G_REV32 + G_LSHR
+      .clampScalar(0, s32, s64);
 
   getActionDefinitionsBuilder({G_ADD, G_SUB, G_MUL, G_AND, G_OR, G_XOR})
       .legalFor({s32, s64, v2s32, v4s32, v4s16, v8s16, v16s8, v8s8})
@@ -791,8 +790,6 @@ bool AArch64LegalizerInfo::legalizeCustom(LegalizerHelper &Helper,
   case TargetOpcode::G_LOAD:
   case TargetOpcode::G_STORE:
     return legalizeLoadStore(MI, MRI, MIRBuilder, Observer);
-  case TargetOpcode::G_BSWAP:
-    return legalizeBSwap(MI, MRI, MIRBuilder);
   case TargetOpcode::G_SHL:
   case TargetOpcode::G_ASHR:
   case TargetOpcode::G_LSHR:
@@ -1047,46 +1044,6 @@ bool AArch64LegalizerInfo::legalizeLoadStore(
   return true;
 }
 
-bool AArch64LegalizerInfo::legalizeBSwap(MachineInstr &MI,
-                                         MachineRegisterInfo &MRI,
-                                         MachineIRBuilder &MIRBuilder) const {
-  assert(MI.getOpcode() == TargetOpcode::G_BSWAP);
-
-  // The <2 x half> case needs special lowering because there isn't an
-  // instruction that does that directly. Instead, we widen to <8 x i8>
-  // and emit a G_REV32 followed by a G_LSHR knowing that instruction selection
-  // will later match them as:
-  //
-  //   rev32.8b v0, v0
-  //   ushr.2s v0, v0, #16
-  //
-  // We could emit those here directly, but it seems better to keep things as
-  // generic as possible through legalization, and avoid committing layering
-  // violations by legalizing & selecting here at the same time.
-
-  Register ValReg = MI.getOperand(1).getReg();
-  assert(LLT::fixed_vector(2, 16) == MRI.getType(ValReg));
-  const LLT v2s32 = LLT::fixed_vector(2, 32);
-  const LLT v8s8 = LLT::fixed_vector(8, 8);
-  const LLT s32 = LLT::scalar(32);
-
-  auto Undef = MIRBuilder.buildUndef(v8s8);
-  auto Insert =
-      MIRBuilder
-          .buildInstr(TargetOpcode::INSERT_SUBREG, {v8s8}, {Undef, ValReg})
-          .addImm(AArch64::ssub);
-  auto Rev32 = MIRBuilder.buildInstr(AArch64::G_REV32, {v8s8}, {Insert});
-  auto Bitcast = MIRBuilder.buildBitcast(v2s32, Rev32);
-  auto Amt = MIRBuilder.buildConstant(v2s32, 16);
-  auto UShr =
-      MIRBuilder.buildInstr(TargetOpcode::G_LSHR, {v2s32}, {Bitcast, Amt});
-  auto Zero = MIRBuilder.buildConstant(s32, 0);
-  auto Extract = MIRBuilder.buildExtractVectorElement(s32, UShr, Zero);
-  MIRBuilder.buildBitcast({MI.getOperand(0).getReg()}, Extract);
-  MI.eraseFromParent();
-  return true;
-}
-
 bool AArch64LegalizerInfo::legalizeVaArg(MachineInstr &MI,
                                          MachineRegisterInfo &MRI,
                                          MachineIRBuilder &MIRBuilder) const {

llvm/lib/Target/AArch64/GISel/AArch64LegalizerInfo.h

@@ -35,8 +35,6 @@ class AArch64LegalizerInfo : public LegalizerInfo {
                          MachineInstr &MI) const override;
 
 private:
-  bool legalizeBSwap(MachineInstr &MI, MachineRegisterInfo &MRI,
-                     MachineIRBuilder &MIRBuilder) const;
   bool legalizeVaArg(MachineInstr &MI, MachineRegisterInfo &MRI,
                      MachineIRBuilder &MIRBuilder) const;
   bool legalizeLoadStore(MachineInstr &MI, MachineRegisterInfo &MRI,

llvm/test/CodeGen/AArch64/GlobalISel/legalize-bswap.mir

@@ -25,33 +25,6 @@ body:             |
     RET_ReallyLR implicit $w0
 ...
 ---
-name:            bswap_2xi16
-tracksRegLiveness: true
-body:             |
-  bb.1:
-    liveins: $s0
-
-    ; CHECK-LABEL: name: bswap_2xi16
-    ; CHECK: liveins: $s0
-    ; CHECK: [[COPY:%[0-9]+]]:_(<2 x s16>) = COPY $s0
-    ; CHECK: [[DEF:%[0-9]+]]:_(<8 x s8>) = G_IMPLICIT_DEF
-    ; CHECK: [[INSERT_SUBREG:%[0-9]+]]:_(<8 x s8>) = INSERT_SUBREG [[DEF]](<8 x s8>), [[COPY]](<2 x s16>), %subreg.ssub
-    ; CHECK: [[REV32_:%[0-9]+]]:_(<8 x s8>) = G_REV32 [[INSERT_SUBREG]]
-    ; CHECK: [[BITCAST:%[0-9]+]]:_(<2 x s32>) = G_BITCAST [[REV32_]](<8 x s8>)
-    ; CHECK: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 16
-    ; CHECK: [[BUILD_VECTOR:%[0-9]+]]:_(<2 x s32>) = G_BUILD_VECTOR [[C]](s32), [[C]](s32)
-    ; CHECK: [[LSHR:%[0-9]+]]:_(<2 x s32>) = G_LSHR [[BITCAST]], [[BUILD_VECTOR]](<2 x s32>)
-    ; CHECK: [[C1:%[0-9]+]]:_(s64) = G_CONSTANT i64 0
-    ; CHECK: [[EVEC:%[0-9]+]]:_(s32) = G_EXTRACT_VECTOR_ELT [[LSHR]](<2 x s32>), [[C1]](s64)
-    ; CHECK: [[BITCAST1:%[0-9]+]]:_(<2 x s16>) = G_BITCAST [[EVEC]](s32)
-    ; CHECK: $s0 = COPY [[BITCAST1]](<2 x s16>)
-    ; CHECK: RET_ReallyLR
-    %0:_(<2 x s16>) = COPY $s0
-    %1:_(<2 x s16>) = G_BSWAP %0
-    $s0 = COPY %1(<2 x s16>)
-    RET_ReallyLR
-...
----
 name:            bswap_s32_legal
 tracksRegLiveness: true
 body:             |

llvm/test/CodeGen/AArch64/GlobalISel/legalizer-info-validation.mir

@@ -564,8 +564,8 @@
 # DEBUG-NEXT: .. type index coverage check SKIPPED: user-defined predicate detected
 # DEBUG-NEXT: .. imm index coverage check SKIPPED: user-defined predicate detected
 # DEBUG-NEXT: G_BSWAP (opcode {{[0-9]+}}): 1 type index, 0 imm indices
-# DEBUG-NEXT: .. type index coverage check SKIPPED: user-defined predicate detected
-# DEBUG-NEXT: .. imm index coverage check SKIPPED: user-defined predicate detected
+# DEBUG-NEXT: .. the first uncovered type index: 1, OK
+# DEBUG-NEXT: .. the first uncovered imm index: 0, OK
 # DEBUG-NEXT: G_BITREVERSE (opcode {{[0-9]+}}): 1 type index, 0 imm indices
 # DEBUG-NEXT: .. the first uncovered type index: 1, OK
 # DEBUG-NEXT: .. the first uncovered imm index: 0, OK