[AArch64][SME] Don't infer -neon from +streaming-sve.

[sdesmalen]

Summary

In Streaming SVE mode full NEON is not available, even though this is
implied from armv8-a. LLVM previously inferred that NEON needed to be
disabled when setting +streaming-sve, but there is no need to infer
this from +streaming-sve, because we can explicitly disable NEON using
LLVM's attribute mechanism. This is specifically relevant because
+streaming-sve is not a user-facing feature, but rather an LLVM internal
feature.

llvm/lib/Target/AArch64/MCTargetDesc/AArch64MCTargetDesc.cpp

 createAArch64MCSubtargetInfo(const Triple &TT, StringRef CPU, StringRef FS) {
   if (CPU.empty()) {
     CPU = "generic";
 
     if (TT.isArm64e())
       CPU = "apple-a12";
   }
 
-  // Most of the NEON instruction set isn't supported in streaming mode on SME
-  // targets, disable NEON unless explicitly requested.
-  bool RequestedNEON = FS.contains("neon");
-  bool RequestedStreamingSVE = FS.contains("streaming-sve");
-  MCSubtargetInfo *STI =
-      createAArch64MCSubtargetInfoImpl(TT, CPU, /*TuneCPU*/ CPU, FS);
-  if (RequestedStreamingSVE && !RequestedNEON &&
-      STI->hasFeature(AArch64::FeatureNEON))
-    STI->ToggleFeature(AArch64::FeatureNEON);
-  return STI;
+  return createAArch64MCSubtargetInfoImpl(TT, CPU, /*TuneCPU*/ CPU, FS);
 }
 
 void AArch64_MC::initLLVMToCVRegMapping(MCRegisterInfo *MRI) {
   // Mapping from CodeView to MC register id.
   static const struct {
     codeview::RegisterId CVReg;
     MCPhysReg Reg;
   } RegMap[] = {

llvm/test/MC/AArch64/SME/streaming-mode-neon-bf16.s

-// RUN: llvm-mc -triple=aarch64 -show-encoding -mattr=+streaming-sve,+bf16 < %s \
+// RUN: llvm-mc -triple=aarch64 -show-encoding -mattr=-neon,+sme < %s \
+// RUN:        | FileCheck %s --check-prefixes=CHECK-ENCODING,CHECK-INST
+// RUN: llvm-mc -triple=aarch64 -show-encoding -mattr=-neon,+streaming-sve,+bf16 < %s \
 // RUN:        | FileCheck %s --check-prefixes=CHECK-ENCODING,CHECK-INST
 // RUN: not llvm-mc -triple=aarch64 -show-encoding -mattr=-neon < %s 2>&1 \
 // RUN:        | FileCheck %s --check-prefix=CHECK-ERROR
-// RUN: llvm-mc -triple=aarch64 -filetype=obj -mattr=+streaming-sve,+bf16 < %s \
+// RUN: llvm-mc -triple=aarch64 -filetype=obj -mattr=-neon,+streaming-sve,+bf16 < %s \
 // RUN:        | llvm-objdump --mattr=+bf16 -d - | FileCheck %s --check-prefix=CHECK-INST
 // Disassemble encoding and check the re-encoding (-show-encoding) matches.
-// RUN: llvm-mc -triple=aarch64 -show-encoding -mattr=+streaming-sve,+bf16 < %s \
+// RUN: llvm-mc -triple=aarch64 -show-encoding -mattr=-neon,+streaming-sve,+bf16 < %s \
 // RUN:        | sed '/.text/d' | sed 's/.*encoding: //g' \
-// RUN:        | llvm-mc -triple=aarch64 -mattr=+streaming-sve,+bf16 -disassemble -show-encoding \
+// RUN:        | llvm-mc -triple=aarch64 -mattr=-neon,+streaming-sve,+bf16 -disassemble -show-encoding \
 // RUN:        | FileCheck %s --check-prefixes=CHECK-ENCODING,CHECK-INST
 
 bfcvt h5, s3
 // CHECK-INST: bfcvt h5, s3
 // CHECK-ENCODING: [0x65,0x40,0x63,0x1e]
-// CHECK-ERROR: instruction requires: bf16
+// CHECK-ERROR: instruction requires: bf16 neon or sme

llvm/test/MC/AArch64/SME/streaming-mode-neon-negative.s

-// RUN: not llvm-mc -triple=aarch64 -show-encoding -mattr=+streaming-sve,+bf16 2>&1 < %s| FileCheck %s
+// RUN: not llvm-mc -triple=aarch64 -show-encoding -mattr=-neon,+sme 2>&1 < %s| FileCheck %s
 
 // ------------------------------------------------------------------------- //
 // Check FABD is illegal in streaming mode
 
 fabd s0, s1, s2
 // CHECK: [[@LINE-1]]:{{[0-9]+}}: error: instruction requires: neon
 // CHECK-NEXT: fabd s0, s1, s2
 // CHECK-NOT: [[@LINE-1]]:{{[0-9]+}}:

llvm/test/MC/AArch64/SME/streaming-mode-neon.s

-// RUN: llvm-mc -triple=aarch64 -show-encoding -mattr=+streaming-sve < %s \
+// RUN: llvm-mc -triple=aarch64 -show-encoding -mattr=-neon,+sme < %s \
+// RUN:        | FileCheck %s --check-prefixes=CHECK-ENCODING,CHECK-INST
+// RUN: llvm-mc -triple=aarch64 -show-encoding -mattr=-neon,+streaming-sve < %s \
 // RUN:        | FileCheck %s --check-prefixes=CHECK-ENCODING,CHECK-INST
 // RUN: not llvm-mc -triple=aarch64 -show-encoding -mattr=-neon < %s 2>&1 \
 // RUN:        | FileCheck %s --check-prefix=CHECK-ERROR
-// RUN: llvm-mc -triple=aarch64 -filetype=obj -mattr=+streaming-sve < %s \
+// RUN: llvm-mc -triple=aarch64 -filetype=obj -mattr=-neon,+streaming-sve < %s \
 // RUN:        | llvm-objdump -d - | FileCheck %s --check-prefix=CHECK-INST
 // Disassemble encoding and check the re-encoding (-show-encoding) matches.
-// RUN: llvm-mc -triple=aarch64 -show-encoding -mattr=+streaming-sve < %s \
+// RUN: llvm-mc -triple=aarch64 -show-encoding -mattr=-neon,+streaming-sve < %s \
 // RUN:        | sed '/.text/d' | sed 's/.*encoding: //g' \
-// RUN:        | llvm-mc -triple=aarch64 -mattr=+streaming-sve -disassemble -show-encoding \
+// RUN:        | llvm-mc -triple=aarch64 -mattr=-neon,+streaming-sve -disassemble -show-encoding \
 // RUN:        | FileCheck %s --check-prefixes=CHECK-ENCODING,CHECK-INST
 
 // Scalar FP instructions
 
 fmulx s0, s1, s2
 // CHECK-INST: fmulx s0, s1, s2
 // CHECK-ENCODING: [0x20,0xdc,0x22,0x5e]
 // CHECK-ERROR: instruction requires: neon or sme

llvm/test/MC/AArch64/SME/streaming-sve-feature.s

-// RUN: llvm-mc -triple=aarch64 -mattr=+streaming-sve,+neon < %s 2>&1 | FileCheck %s
-// RUN: not llvm-mc -triple=aarch64 -mattr=+streaming-sve < %s 2>&1 | FileCheck %s --check-prefix=CHECK-ERROR
+// RUN: llvm-mc -triple=aarch64 -mattr=+sme < %s 2>&1 | FileCheck %s
+// RUN: not llvm-mc -triple=aarch64 -mattr=-neon,+sme < %s 2>&1 | FileCheck %s --check-prefix=CHECK-ERROR
 
 // Verify NEON is disabled when targeting streaming mode, if it's not
 // explicitly requested.
 add v0.8b, v1.8b, v2.8b
 // CHECK: add v0.8b, v1.8b, v2.8b
 // CHECK-ERROR: error: instruction requires: neon