Fix encoding for p regs. Fix regression test.

Author: efriedma-quic

llvm/lib/MC/MCWin64EH.cpp

@@ -669,7 +669,7 @@ static void ARM64EmitUnwindCode(MCStreamer &streamer,
     assert(inst.Offset < 256);
     b = 0xE7;
     streamer.emitInt8(b);
-    reg = inst.Register - 4;
+    reg = inst.Register;
     b = ((inst.Offset & 0xC0) >> 1) | 0x10 | reg;
     streamer.emitInt8(b);
     b = 0xC0 | (inst.Offset & 0x3F);

llvm/test/MC/AArch64/seh.s

@@ -56,7 +56,7 @@
 // CHECK-NEXT:     ExceptionData {
 // CHECK-NEXT:       FunctionLength: 172
 // CHECK:            Prologue [
-// CHECK-NEXT:         0xe712c3            ; str p6, [sp, #3, mul vl]
+// CHECK-NEXT:         0xe716c3            ; str p6, [sp, #3, mul vl]
 // CHECK-NEXT:         0xe703c5            ; str z11, [sp, #5, mul vl]
 // CHECK-NEXT:         0xdf05              ; addvl sp, #-5
 // CHECK-NEXT:         0xe76983            ; stp q9, q10, [sp, #-64]!

llvm/test/tools/llvm-readobj/COFF/arm64-win-error1.s

@@ -6,7 +6,7 @@
 // RUN:   | llvm-readobj --unwind - | FileCheck %s
 
 // CHECK:     Prologue [
-// CHECK:        0xdf                ; Bad opcode!
+// CHECK:        0xef                ; Bad opcode!
 // CHECK:        0xff                ; Bad opcode!
 // CHECK:        0xd600              ; stp x19, lr, [sp, #0]
 // CHECK:        0x01                ; sub sp, #16
@@ -49,6 +49,6 @@
 	.long		0x10800012
 	.long 		0x8
 	.long 		0xe
-	.long 		0x00d6ffdf
+	.long 		0x00d6ffef
 	.long 		0xe3e3e401
 

llvm/tools/llvm-readobj/ARMWinEHPrinter.cpp

@@ -991,7 +991,7 @@ bool Decoder::opcode_save_zreg(const uint8_t *OC, unsigned &Offset,
 
 bool Decoder::opcode_save_preg(const uint8_t *OC, unsigned &Offset,
                                unsigned Length, bool Prologue) {
-  uint32_t Reg = (OC[Offset + 1] & 0x0F) + 4;
+  uint32_t Reg = (OC[Offset + 1] & 0x0F);
   uint32_t Off = ((OC[Offset + 1] & 0x60) << 1) | (OC[Offset + 2] & 0x3F);
   SW.startLine() << format(
       "0x%02x%02x%02x            ; %s p%u, [sp, #%u, mul vl]\n", OC[Offset],