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

1 files changed, 44 insertions, 3 deletions

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);
 }