From 510862e50c4016a6ac5557712b7e01e8d58bece0 Mon Sep 17 00:00:00 2001
From: MerryMage <MerryMage@users.noreply.github.com>
Date: Sun, 25 Apr 2021 23:19:32 +0100
Subject: [PATCH] backend/x64: Change V flag testing to cmp instead of add

Prefer a non-destructive read to a destructive read.
---
 src/backend/x64/emit_x64.cpp                 | 12 ++++++------
 src/backend/x64/emit_x64_data_processing.cpp | 12 ++++++------
 2 files changed, 12 insertions(+), 12 deletions(-)

diff --git a/src/backend/x64/emit_x64.cpp b/src/backend/x64/emit_x64.cpp
index a71200c5..817de5f5 100644
--- a/src/backend/x64/emit_x64.cpp
+++ b/src/backend/x64/emit_x64.cpp
@@ -219,11 +219,11 @@ Xbyak::Label EmitX64::EmitCond(IR::Cond cond) {
         code.jns(pass);
         break;
     case IR::Cond::VS: //v
-        code.add(al, 0x7F);
+        code.cmp(al, 0x81);
         code.jo(pass);
         break;
     case IR::Cond::VC: //!v
-        code.add(al, 0x7F);
+        code.cmp(al, 0x81);
         code.jno(pass);
         break;
     case IR::Cond::HI: //c & !z
@@ -237,22 +237,22 @@ Xbyak::Label EmitX64::EmitCond(IR::Cond cond) {
         code.jna(pass);
         break;
     case IR::Cond::GE: // n == v
-        code.add(al, 0x7F);
+        code.cmp(al, 0x81);
         code.sahf();
         code.jge(pass);
         break;
     case IR::Cond::LT: // n != v
-        code.add(al, 0x7F);
+        code.cmp(al, 0x81);
         code.sahf();
         code.jl(pass);
         break;
     case IR::Cond::GT: // !z & (n == v)
-        code.add(al, 0x7F);
+        code.cmp(al, 0x81);
         code.sahf();
         code.jg(pass);
         break;
     case IR::Cond::LE: // z | (n != v)
-        code.add(al, 0x7F);
+        code.cmp(al, 0x81);
         code.sahf();
         code.jle(pass);
         break;
diff --git a/src/backend/x64/emit_x64_data_processing.cpp b/src/backend/x64/emit_x64_data_processing.cpp
index eadbf222..5a3d179d 100644
--- a/src/backend/x64/emit_x64_data_processing.cpp
+++ b/src/backend/x64/emit_x64_data_processing.cpp
@@ -171,11 +171,11 @@ static void EmitConditionalSelect(BlockOfCode& code, EmitContext& ctx, IR::Inst*
         code.cmovns(else_, then_);
         break;
     case IR::Cond::VS: //v
-        code.add(nzcv.cvt8(), 0x7F);
+        code.cmp(nzcv.cvt8(), 0x81);
         code.cmovo(else_, then_);
         break;
     case IR::Cond::VC: //!v
-        code.add(nzcv.cvt8(), 0x7F);
+        code.cmp(nzcv.cvt8(), 0x81);
         code.cmovno(else_, then_);
         break;
     case IR::Cond::HI: //c & !z
@@ -189,22 +189,22 @@ static void EmitConditionalSelect(BlockOfCode& code, EmitContext& ctx, IR::Inst*
         code.cmovna(else_, then_);
         break;
     case IR::Cond::GE: // n == v
-        code.add(nzcv.cvt8(), 0x7F);
+        code.cmp(nzcv.cvt8(), 0x81);
         code.sahf();
         code.cmovge(else_, then_);
         break;
     case IR::Cond::LT: // n != v
-        code.add(nzcv.cvt8(), 0x7F);
+        code.cmp(nzcv.cvt8(), 0x81);
         code.sahf();
         code.cmovl(else_, then_);
         break;
     case IR::Cond::GT: // !z & (n == v)
-        code.add(nzcv.cvt8(), 0x7F);
+        code.cmp(nzcv.cvt8(), 0x81);
         code.sahf();
         code.cmovg(else_, then_);
         break;
     case IR::Cond::LE: // z | (n != v)
-        code.add(nzcv.cvt8(), 0x7F);
+        code.cmp(nzcv.cvt8(), 0x81);
         code.sahf();
         code.cmovle(else_, then_);
         break;