[AArch64][v8.5A] Add speculation barrier to AArch64 instruction set

[olista01]

Summary

This is a new barrier which limits speculative execution of the
instructions following it.

Patch by Pablo Barrio!

[t.p.northover]

This looks fine.

[t.p.northover]

Actually, sorry. I think this should be marked HasSideEffects.

[olista01]

Add hasSideEffects.

[t.p.northover]

Thanks. Looks fine now.

lib/Target/AArch64/AArch64.td

 
 def FeatureAltFPCmp : SubtargetFeature<"altnzcv", "HasAlternativeNZCV", "true",
   "Enable alternative NZCV format for floating point comparisons">;
 
 def FeatureFRIntNNT : SubtargetFeature<"fptoint", "HasFRIntNNT", "true",
   "Enable FRInt[32|64][Z|X] instructions that round a floating-point number to "
   "an integer (in FP format) forcing it to fit into a 32- or 64-bit int" >;
 
+def FeatureSpecCtrl : SubtargetFeature<"specctrl", "HasSpecCtrl", "true",
+  "Enable speculation control barrier" >;
+
 //===----------------------------------------------------------------------===//
 // Architectures.
 //
 
 def HasV8_1aOps : SubtargetFeature<"v8.1a", "HasV8_1aOps", "true",
   "Support ARM v8.1a instructions", [FeatureCRC, FeatureLSE, FeatureRDM]>;
 
 def HasV8_2aOps : SubtargetFeature<"v8.2a", "HasV8_2aOps", "true",
   "Support ARM v8.2a instructions", [HasV8_1aOps, FeatureRAS]>;
 
 def HasV8_3aOps : SubtargetFeature<"v8.3a", "HasV8_3aOps", "true",
   "Support ARM v8.3a instructions", [HasV8_2aOps, FeatureRCPC]>;
 
 def HasV8_4aOps : SubtargetFeature<"v8.4a", "HasV8_4aOps", "true",
   "Support ARM v8.4a instructions", [HasV8_3aOps, FeatureDotProd]>;
 
 def HasV8_5aOps : SubtargetFeature<
   "v8.5a", "HasV8_5aOps", "true", "Support ARM v8.5a instructions",
-  [HasV8_4aOps, FeatureAltFPCmp, FeatureFRIntNNT]
+  [HasV8_4aOps, FeatureAltFPCmp, FeatureFRIntNNT, FeatureSpecCtrl]
 >;
 
 //===----------------------------------------------------------------------===//
 // Register File Description
 //===----------------------------------------------------------------------===//
 
 include "AArch64RegisterInfo.td"
 include "AArch64RegisterBanks.td"

lib/Target/AArch64/AArch64InstrInfo.td

 def HasSVE           : Predicate<"Subtarget->hasSVE()">,
                                  AssemblerPredicate<"FeatureSVE", "sve">;
 def HasRCPC          : Predicate<"Subtarget->hasRCPC()">,
                                  AssemblerPredicate<"FeatureRCPC", "rcpc">;
 def HasAltNZCV       : Predicate<"Subtarget->hasAlternativeNZCV()">,
                        AssemblerPredicate<"FeatureAltFPCmp", "altnzcv">;
 def HasFRIntNNT      : Predicate<"Subtarget->hasFRIntNNT()">,
                        AssemblerPredicate<"FeatureFRIntNNT", "fptoint">;
+def HasSpecCtrl      : Predicate<"Subtarget->hasSpecCtrl()">,
+                       AssemblerPredicate<"FeatureSpecCtrl", "specctrl">;
 def IsLE             : Predicate<"Subtarget->isLittleEndian()">;
 def IsBE             : Predicate<"!Subtarget->isLittleEndian()">;
 def UseAlternateSExtLoadCVTF32
     : Predicate<"Subtarget->useAlternateSExtLoadCVTF32Pattern()">;
 
 def UseNegativeImmediates
     : Predicate<"false">, AssemblerPredicate<"!FeatureNoNegativeImmediates",
                                              "NegativeImmediates">;

 }
 
 def AXFLAG : PstateWriteSimple<(ins), "axflag", "">, Sched<[WriteSys]> {
   let Inst{18-16} = 0b000;
   let Inst{11-8} = 0b0000;
   let Unpredictable{11-8} = 0b1111;
   let Inst{7-5} = 0b010;
 }
-
 } // HasAltNZCV
 
+
+// Armv8.5-A speculation barrier
+def SB : SimpleSystemI<0, (ins), "sb", "">, Sched<[]> {
+    let Inst{20-5} = 0b0001100110000111;
+    let Unpredictable{11-8} = 0b1111;
+    let Predicates = [HasSpecCtrl];
+}
+
 def : InstAlias<"clrex", (CLREX 0xf)>;
 def : InstAlias<"isb", (ISB 0xf)>;
 
 def MRS    : MRSI;
 def MSR    : MSRI;
 def MSRpstateImm1 : MSRpstateImm0_1;
 def MSRpstateImm4 : MSRpstateImm0_15;
 

lib/Target/AArch64/AArch64Subtarget.h

protected:
   bool HasLSLFast = false;
   bool HasSVE = false;
   bool HasRCPC = false;
   bool HasAggressiveFMA = false;
 
   // Armv8.5-A Extensions
   bool HasAlternativeNZCV = false;
   bool HasFRIntNNT = false;
+  bool HasSpecCtrl = false;
 
   // HasZeroCycleRegMove - Has zero-cycle register mov instructions.
   bool HasZeroCycleRegMove = false;
 
   // HasZeroCycleZeroing - Has zero-cycle zeroing instructions.
   bool HasZeroCycleZeroing = false;
   bool HasZeroCycleZeroingFPWorkaround = false;
 
public:
   bool hasFP16FML() const { return HasFP16FML; }
   bool hasSPE() const { return HasSPE; }
   bool hasLSLFast() const { return HasLSLFast; }
   bool hasSVE() const { return HasSVE; }
   bool hasRCPC() const { return HasRCPC; }
   bool hasAggressiveFMA() const { return HasAggressiveFMA; }
   bool hasAlternativeNZCV() const { return HasAlternativeNZCV; }
   bool hasFRIntNNT() { return HasFRIntNNT; }
+  bool hasSpecCtrl() { return HasSpecCtrl; }
 
   bool isLittleEndian() const { return IsLittle; }
 
   bool isTargetDarwin() const { return TargetTriple.isOSDarwin(); }
   bool isTargetIOS() const { return TargetTriple.isiOS(); }
   bool isTargetLinux() const { return TargetTriple.isOSLinux(); }
   bool isTargetWindows() const { return TargetTriple.isOSWindows(); }
   bool isTargetAndroid() const { return TargetTriple.isAndroid(); }

test/MC/AArch64/armv8.5a-specctrl.s

+// RUN:     llvm-mc -triple aarch64-none-linux-gnu -show-encoding -mattr=+specctrl < %s      | FileCheck %s
+// RUN:     llvm-mc -triple aarch64-none-linux-gnu -show-encoding -mattr=+v8.5a    < %s      | FileCheck %s
+// RUN: not llvm-mc -triple aarch64-none-linux-gnu -show-encoding -mattr=-specctrl < %s 2>&1 | FileCheck %s --check-prefix=NOSB
+
+// Flag manipulation
+sb
+
+// CHECK: sb // encoding: [0xff,0x30,0x03,0xd5]
+
+// NOSB: instruction requires: specctrl
+// NOSB-NEXT: sb

test/MC/Disassembler/AArch64/armv8.5a-specctrl.txt

+# RUN: llvm-mc -triple=aarch64-none-linux-gnu -mattr=+specctrl -disassemble < %s      | FileCheck %s
+# RUN: llvm-mc -triple=aarch64-none-linux-gnu -mattr=+v8.5a    -disassemble < %s      | FileCheck %s
+# RUN: llvm-mc -triple=aarch64-none-linux-gnu -mattr=-specctrl -disassemble < %s 2>&1 | FileCheck %s --check-prefix=NOSB
+
+# New reg
+0xff 0x30 0x03 0xd5
+
+# CHECK: sb
+# NOSB:  msr S0_3_C3_C0_7, xzr