[AArch64][v8.5A] Add PSTATE manipulation instructions XAFlag and AXFlag

These new instructions manipluate the NZCV bits, to convert between the
regular Arm floating-point comare format and an alternative format.

Patch by Pablo Barrio!

Differential revision: https://reviews.llvm.org/D52473

llvm-svn: 343187

4 files changed, 35 insertions, 3 deletions

diff --git a/llvm/lib/Target/AArch64/AArch64.td b/llvm/lib/Target/AArch64/AArch64.td
index fc3900bd939..592c7e07b94 100644
--- a/llvm/lib/Target/AArch64/AArch64.td
+++ b/llvm/lib/Target/AArch64/AArch64.td
@@ -204,6 +204,9 @@ def FeatureAggressiveFMA :
                    "true",
                    "Enable Aggressive FMA for floating-point.">;
 
+def FeatureAltFPCmp : SubtargetFeature<"altnzcv", "HasAlternativeNZCV", "true",
+  "Enable alternative NZCV format for floating point comparisons">;
+
 //===----------------------------------------------------------------------===//
 // Architectures.
 //
@@ -221,7 +224,7 @@ 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]>;
+  "Support ARM v8.5a instructions", [HasV8_4aOps, FeatureAltFPCmp]>;
 
 //===----------------------------------------------------------------------===//
 // Register File Description
diff --git a/llvm/lib/Target/AArch64/AArch64InstrInfo.td b/llvm/lib/Target/AArch64/AArch64InstrInfo.td
index 97418985b8a..83bec32da79 100644
--- a/llvm/lib/Target/AArch64/AArch64InstrInfo.td
+++ b/llvm/lib/Target/AArch64/AArch64InstrInfo.td
@@ -62,7 +62,8 @@ 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 IsLE             : Predicate<"Subtarget->isLittleEndian()">;
 def IsBE             : Predicate<"!Subtarget->isLittleEndian()">;
 def UseAlternateSExtLoadCVTF32
@@ -608,6 +609,25 @@ def RMIF   : FlagRotate<(ins GPR64:$Rn, uimm6:$imm, imm0_15:$mask), "rmif",
                         "{\t$Rn, $imm, $mask}">;
 } // HasV8_4a
 
+// v8.5 flag manipulation instructions
+let Predicates = [HasAltNZCV], Uses = [NZCV], Defs = [NZCV] in {
+
+def XAFLAG : PstateWriteSimple<(ins), "xaflag", "">, Sched<[WriteSys]> {
+  let Inst{18-16} = 0b000;
+  let Inst{11-8} = 0b0000;
+  let Unpredictable{11-8} = 0b1111;
+  let Inst{7-5} = 0b001;
+}
+
+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
+
 def : InstAlias<"clrex", (CLREX 0xf)>;
 def : InstAlias<"isb", (ISB 0xf)>;
 
diff --git a/llvm/lib/Target/AArch64/AArch64Subtarget.h b/llvm/lib/Target/AArch64/AArch64Subtarget.h
index 992d211dba0..bf60a0fd269 100644
--- a/llvm/lib/Target/AArch64/AArch64Subtarget.h
+++ b/llvm/lib/Target/AArch64/AArch64Subtarget.h
@@ -94,6 +94,9 @@ protected:
   bool HasRCPC = false;
   bool HasAggressiveFMA = false;
 
+  // Armv8.5-A Extensions
+  bool HasAlternativeNZCV = false;
+
   // HasZeroCycleRegMove - Has zero-cycle register mov instructions.
   bool HasZeroCycleRegMove = false;
 
@@ -306,6 +309,7 @@ public:
   bool hasSVE() const { return HasSVE; }
   bool hasRCPC() const { return HasRCPC; }
   bool hasAggressiveFMA() const { return HasAggressiveFMA; }
+  bool hasAlternativeNZCV() const { return HasAlternativeNZCV; }
 
   bool isLittleEndian() const { return IsLittle; }
 
diff --git a/llvm/lib/Target/AArch64/Disassembler/AArch64Disassembler.cpp b/llvm/lib/Target/AArch64/Disassembler/AArch64Disassembler.cpp
index f73670788f8..d2f672643b8 100644
--- a/llvm/lib/Target/AArch64/Disassembler/AArch64Disassembler.cpp
+++ b/llvm/lib/Target/AArch64/Disassembler/AArch64Disassembler.cpp
@@ -1712,9 +1712,14 @@ static DecodeStatus DecodeSystemPStateInstruction(MCInst &Inst, uint32_t insn,
   uint64_t op1 = fieldFromInstruction(insn, 16, 3);
   uint64_t op2 = fieldFromInstruction(insn, 5, 3);
   uint64_t crm = fieldFromInstruction(insn, 8, 4);
-
   uint64_t pstate_field = (op1 << 3) | op2;
 
+  switch (pstate_field) {
+  case 0x01: // XAFlag
+  case 0x02: // AXFlag
+    return Fail;
+  }
+
   if ((pstate_field == AArch64PState::PAN  ||
        pstate_field == AArch64PState::UAO) && crm > 1)
     return Fail;