[X86][MC] Support encoding/decoding for PUSHP/POPP (#73092)

A PUSH and its corresponding POP may be marked with a 1-bit Push-Pop Acceleration (PPX)
hint to indicate that the POP reads the value written by the PUSH from the stack. The PPX hint
is encoded by setting REX2.W = 1 and is applicable only to PUSH with opcode 0x50+rd and POP
with opcode 0x58+rd in the legacy space. It is not applicable to any other variants of PUSH and POP.

Author: KanRobert

llvm/lib/Target/X86/Disassembler/X86Disassembler.cpp

@@ -1257,9 +1257,9 @@ static int getInstructionID(struct InternalInstruction *insn,
     attrMask &= ~ATTR_ADSIZE;
   }
 
-  // Absolute jump need special handling
+  // Absolute jump and pushp/popp need special handling
   if (insn->rex2ExtensionPrefix[0] == 0xd5 && insn->opcodeType == ONEBYTE &&
-      insn->opcode == 0xA1)
+      (insn->opcode == 0xA1 || (insn->opcode & 0xf0) == 0x50))
     attrMask |= ATTR_REX2;
 
   if (insn->mode == MODE_16BIT) {

llvm/lib/Target/X86/X86InstrMisc.td

@@ -161,6 +161,8 @@ let isCodeGenOnly = 1, ForceDisassemble = 1 in {
 def POP64rmr: I<0x8F, MRM0r, (outs GR64:$reg), (ins), "pop{q}\t$reg", []>,
                 OpSize32, Requires<[In64BitMode]>;
 } // isCodeGenOnly = 1, ForceDisassemble = 1
+def POPP64r  : I<0x58, AddRegFrm, (outs GR64:$reg), (ins), "popp\t$reg", []>,
+                 REX_W, ExplicitREX2Prefix, Requires<[In64BitMode]>;
 } // mayLoad, SchedRW
 let mayLoad = 1, mayStore = 1, SchedRW = [WriteCopy] in
 def POP64rmm: I<0x8F, MRM0m, (outs), (ins i64mem:$dst), "pop{q}\t$dst", []>,
@@ -173,6 +175,8 @@ let isCodeGenOnly = 1, ForceDisassemble = 1 in {
 def PUSH64rmr: I<0xFF, MRM6r, (outs), (ins GR64:$reg), "push{q}\t$reg", []>,
                  OpSize32, Requires<[In64BitMode]>;
 } // isCodeGenOnly = 1, ForceDisassemble = 1
+def PUSHP64r  : I<0x50, AddRegFrm, (outs), (ins GR64:$reg), "pushp\t$reg", []>,
+                  REX_W, ExplicitREX2Prefix, Requires<[In64BitMode]>;
 } // mayStore, SchedRW
 let mayLoad = 1, mayStore = 1, SchedRW = [WriteCopy] in {
 def PUSH64rmm: I<0xFF, MRM6m, (outs), (ins i64mem:$src), "push{q}\t$src", []>,

llvm/test/MC/Disassembler/X86/apx/pushp-popp.txt

@@ -0,0 +1,34 @@
+# RUN: llvm-mc -triple x86_64 -disassemble %s | FileCheck %s --check-prefix=ATT
+# RUN: llvm-mc -triple x86_64 -disassemble -output-asm-variant=1 %s | FileCheck %s --check-prefix=INTEL
+
+# ATT:   pushp	%rax
+# INTEL: pushp	rax
+0xd5,0x08,0x50
+
+# ATT:   pushp	%rbx
+# INTEL: pushp	rbx
+0xd5,0x08,0x53
+
+# ATT:   pushp	%r15
+# INTEL: pushp	r15
+0xd5,0x09,0x57
+
+# ATT:   pushp	%r16
+# INTEL: pushp	r16
+0xd5,0x18,0x50
+
+# ATT:   popp	%rax
+# INTEL: popp	rax
+0xd5,0x08,0x58
+
+# ATT:   popp	%rbx
+# INTEL: popp	rbx
+0xd5,0x08,0x5b
+
+# ATT:   popp	%r15
+# INTEL: popp	r15
+0xd5,0x09,0x5f
+
+# ATT:   popp	%r16
+# INTEL: popp	r16
+0xd5,0x18,0x58

llvm/test/MC/X86/apx/pushp-popp-att.s

@@ -0,0 +1,31 @@
+# RUN: llvm-mc -triple x86_64 -show-encoding %s | FileCheck %s
+# RUN: not llvm-mc -triple i386 -show-encoding %s 2>&1 | FileCheck %s --check-prefix=ERROR
+
+# ERROR-COUNT-8: error:
+# ERROR-NOT: error:
+
+# CHECK: pushp	%rax
+# CHECK: encoding: [0xd5,0x08,0x50]
+         pushp	%rax
+# CHECK: pushp	%rbx
+# CHECK: encoding: [0xd5,0x08,0x53]
+         pushp	%rbx
+# CHECK: pushp	%r15
+# CHECK: encoding: [0xd5,0x09,0x57]
+         pushp	%r15
+# CHECK: pushp	%r16
+# CHECK: encoding: [0xd5,0x18,0x50]
+         pushp	%r16
+
+# CHECK: popp	%rax
+# CHECK: encoding: [0xd5,0x08,0x58]
+         popp	%rax
+# CHECK: popp	%rbx
+# CHECK: encoding: [0xd5,0x08,0x5b]
+         popp	%rbx
+# CHECK: popp	%r15
+# CHECK: encoding: [0xd5,0x09,0x5f]
+         popp	%r15
+# CHECK: popp	%r16
+# CHECK: encoding: [0xd5,0x18,0x58]
+         popp	%r16

llvm/test/MC/X86/apx/pushp-popp-intel.s

@@ -0,0 +1,27 @@
+# RUN: llvm-mc -triple x86_64 -show-encoding -x86-asm-syntax=intel -output-asm-variant=1 %s | FileCheck %s
+
+# CHECK: pushp	rax
+# CHECK: encoding: [0xd5,0x08,0x50]
+         pushp	rax
+# CHECK: pushp	rbx
+# CHECK: encoding: [0xd5,0x08,0x53]
+         pushp	rbx
+# CHECK: pushp	r15
+# CHECK: encoding: [0xd5,0x09,0x57]
+         pushp	r15
+# CHECK: pushp	r16
+# CHECK: encoding: [0xd5,0x18,0x50]
+         pushp	r16
+
+# CHECK: popp	rax
+# CHECK: encoding: [0xd5,0x08,0x58]
+         popp	rax
+# CHECK: popp	rbx
+# CHECK: encoding: [0xd5,0x08,0x5b]
+         popp	rbx
+# CHECK: popp	r15
+# CHECK: encoding: [0xd5,0x09,0x5f]
+         popp	r15
+# CHECK: popp	r16
+# CHECK: encoding: [0xd5,0x18,0x58]
+         popp	r16