From b50ceebb814f28a6ade94974d3e8614c8585760e Mon Sep 17 00:00:00 2001
From: Ulya Trafimovich <skvadrik@google.com>
Date: Mon, 12 Jul 2021 14:20:16 +0100
Subject: x86: Add missing variants for XCHG and tests for this instruction.

Add XCHG variants when both operands are registers. Handle the special
case when at least one of the register operands is EAX/AX. Add tests for
the new variants and for other variants that previously weren't tested.

Bug: 65872996
Test: m test-art-host-gtest
Change-Id: I1e80d1b86f3d2e804b90c2a181e4eabded30d8ae
---
 compiler/utils/x86/assembler_x86.cc | 47 ++++++++++++++++++++++++++++++++++---
 1 file changed, 44 insertions(+), 3 deletions(-)

(limited to 'compiler/utils/x86/assembler_x86.cc')

diff --git a/compiler/utils/x86/assembler_x86.cc b/compiler/utils/x86/assembler_x86.cc
index adc7bcc0f4..b6708de81c 100644
--- a/compiler/utils/x86/assembler_x86.cc
+++ b/compiler/utils/x86/assembler_x86.cc
@@ -2887,9 +2887,22 @@ void X86Assembler::fprem() {
 }
 
 
-void X86Assembler::xchgb(Register reg, const Address& address) {
-  // For testing purpose
-  xchgb(static_cast<ByteRegister>(reg), address);
+bool X86Assembler::try_xchg_eax(Register dst, Register src) {
+  if (src != EAX && dst != EAX) {
+    return false;
+  }
+  if (dst == EAX) {
+    std::swap(src, dst);
+  }
+  EmitUint8(0x90 + dst);
+  return true;
+}
+
+
+void X86Assembler::xchgb(ByteRegister dst, ByteRegister src) {
+  AssemblerBuffer::EnsureCapacity ensured(&buffer_);
+  EmitUint8(0x86);
+  EmitRegisterOperand(dst, src);
 }
 
 
@@ -2900,6 +2913,29 @@ void X86Assembler::xchgb(ByteRegister reg, const Address& address) {
 }
 
 
+void X86Assembler::xchgb(Register dst, Register src) {
+  xchgb(static_cast<ByteRegister>(dst), static_cast<ByteRegister>(src));
+}
+
+
+void X86Assembler::xchgb(Register reg, const Address& address) {
+  xchgb(static_cast<ByteRegister>(reg), address);
+}
+
+
+void X86Assembler::xchgw(Register dst, Register src) {
+  AssemblerBuffer::EnsureCapacity ensured(&buffer_);
+  EmitOperandSizeOverride();
+  if (try_xchg_eax(dst, src)) {
+    // A short version for AX.
+    return;
+  }
+  // General case.
+  EmitUint8(0x87);
+  EmitRegisterOperand(dst, src);
+}
+
+
 void X86Assembler::xchgw(Register reg, const Address& address) {
   AssemblerBuffer::EnsureCapacity ensured(&buffer_);
   EmitOperandSizeOverride();
@@ -2910,6 +2946,11 @@ void X86Assembler::xchgw(Register reg, const Address& address) {
 
 void X86Assembler::xchgl(Register dst, Register src) {
   AssemblerBuffer::EnsureCapacity ensured(&buffer_);
+  if (try_xchg_eax(dst, src)) {
+    // A short version for EAX.
+    return;
+  }
+  // General case.
   EmitUint8(0x87);
   EmitRegisterOperand(dst, src);
 }
-- 
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