[AArch64][PAC] Expand blend(reg, imm) operation in aarch64-pauth pass (#74729)

In preparation for implementing code generation for more @llvm.ptrauth.* intrinsics, move the expansion of blend(register, small integer) variant of @llvm.ptrauth.blend to the AArch64PointerAuth pass, where most other PAuth-related code generation takes place.

Author: atrosinenko

llvm/lib/Target/AArch64/AArch64InstrInfo.td

@@ -1581,6 +1581,9 @@ def PAUTH_PROLOGUE : Pseudo<(outs), (ins), []>, Sched<[]>;
 def PAUTH_EPILOGUE : Pseudo<(outs), (ins), []>, Sched<[]>;
 }
 
+def PAUTH_BLEND : Pseudo<(outs GPR64:$disc),
+                         (ins GPR64:$addr_disc, i32imm:$int_disc), []>, Sched<[]>;
+
 // These pointer authentication instructions require armv8.3a
 let Predicates = [HasPAuth] in {
 
@@ -9317,12 +9320,10 @@ let Predicates = [HasMOPS, HasMTE], Defs = [NZCV], Size = 12, mayLoad = 0, maySt
 //-----------------------------------------------------------------------------
 // v8.3 Pointer Authentication late patterns
 
-let Predicates = [HasPAuth] in {
 def : Pat<(int_ptrauth_blend GPR64:$Rd, imm64_0_65535:$imm),
-          (MOVKXi GPR64:$Rd, (trunc_imm imm64_0_65535:$imm), 48)>;
+          (PAUTH_BLEND GPR64:$Rd, (trunc_imm imm64_0_65535:$imm))>;
 def : Pat<(int_ptrauth_blend GPR64:$Rd, GPR64:$Rn),
           (BFMXri GPR64:$Rd, GPR64:$Rn, 16, 15)>;
-}
 
 //-----------------------------------------------------------------------------
 

llvm/lib/Target/AArch64/AArch64PointerAuth.cpp

@@ -46,6 +46,13 @@ class AArch64PointerAuth : public MachineFunctionPass {
   void authenticateLR(MachineFunction &MF,
                       MachineBasicBlock::iterator MBBI) const;
 
+  /// Stores blend(AddrDisc, IntDisc) to the Result register.
+  void emitBlend(MachineBasicBlock::iterator MBBI, Register Result,
+                 Register AddrDisc, unsigned IntDisc) const;
+
+  /// Expands PAUTH_BLEND pseudo instruction.
+  void expandPAuthBlend(MachineBasicBlock::iterator MBBI) const;
+
   bool checkAuthenticatedLR(MachineBasicBlock::iterator TI) const;
 };
 
@@ -359,6 +366,32 @@ bool AArch64PointerAuth::checkAuthenticatedLR(
   return true;
 }
 
+void AArch64PointerAuth::emitBlend(MachineBasicBlock::iterator MBBI,
+                                   Register Result, Register AddrDisc,
+                                   unsigned IntDisc) const {
+  MachineBasicBlock &MBB = *MBBI->getParent();
+  DebugLoc DL = MBBI->getDebugLoc();
+
+  if (Result != AddrDisc)
+    BuildMI(MBB, MBBI, DL, TII->get(AArch64::ORRXrs), Result)
+        .addReg(AArch64::XZR)
+        .addReg(AddrDisc)
+        .addImm(0);
+
+  BuildMI(MBB, MBBI, DL, TII->get(AArch64::MOVKXi), Result)
+      .addReg(Result)
+      .addImm(IntDisc)
+      .addImm(48);
+}
+
+void AArch64PointerAuth::expandPAuthBlend(
+    MachineBasicBlock::iterator MBBI) const {
+  Register ResultReg = MBBI->getOperand(0).getReg();
+  Register AddrDisc = MBBI->getOperand(1).getReg();
+  unsigned IntDisc = MBBI->getOperand(2).getImm();
+  emitBlend(MBBI, ResultReg, AddrDisc, IntDisc);
+}
+
 bool AArch64PointerAuth::runOnMachineFunction(MachineFunction &MF) {
   const auto *MFnI = MF.getInfo<AArch64FunctionInfo>();
 
@@ -390,6 +423,7 @@ bool AArch64PointerAuth::runOnMachineFunction(MachineFunction &MF) {
         break;
       case AArch64::PAUTH_PROLOGUE:
       case AArch64::PAUTH_EPILOGUE:
+      case AArch64::PAUTH_BLEND:
         assert(!MI.isBundled());
         PAuthPseudoInstrs.push_back(MI.getIterator());
         break;
@@ -406,6 +440,9 @@ bool AArch64PointerAuth::runOnMachineFunction(MachineFunction &MF) {
       authenticateLR(MF, It);
       HasAuthenticationInstrs = true;
       break;
+    case AArch64::PAUTH_BLEND:
+      expandPAuthBlend(It);
+      break;
     default:
       llvm_unreachable("Unhandled opcode");
     }

llvm/test/CodeGen/AArch64/ptrauth-pseudo-instructions.mir

@@ -0,0 +1,27 @@
+# RUN: llc -mtriple=aarch64--- -run-pass=aarch64-ptrauth -verify-machineinstrs %s -o - | FileCheck %s
+
+# Test the corner cases that cannot be reliably tested using LLVM IR as input.
+
+--- |
+  define i64 @blend_untied(i64 %unused, i64 %ptr_arg) {
+    ret i64 0
+  }
+...
+---
+# Check that the input register is copied to the output one, if not tied.
+
+name:            blend_untied
+tracksRegLiveness: true
+body:             |
+  bb.0:
+  liveins: $lr, $x0, $x1
+    $x0 = PAUTH_BLEND $x1, 42
+    RET undef $lr
+
+# CHECK:       liveins: $lr, $x0, $x1
+# CHECK-NEXT:    {{^ +$}}
+# CHECK-NEXT:    $x0 = ORRXrs $xzr, $x1, 0
+# CHECK-NEXT:    $x0 = MOVKXi $x0, 42, 48
+# CHECK-NEXT:    RET undef $lr
+
+...