From 1530dc6c5502bc3b6e2692b93d8658c1ea02502b Mon Sep 17 00:00:00 2001
From: nitrix <me@nitrix.one>
Date: Thu, 5 Mar 2020 17:13:19 +0100
Subject: [PATCH] sign extend rax into rbx before calling idiv, the replaces
 the rbx zeroing

---
 src/main/java/de/hsrm/compiler/Klang/visitors/GenASM.java | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/main/java/de/hsrm/compiler/Klang/visitors/GenASM.java b/src/main/java/de/hsrm/compiler/Klang/visitors/GenASM.java
index d75e87f..f8edb42 100644
--- a/src/main/java/de/hsrm/compiler/Klang/visitors/GenASM.java
+++ b/src/main/java/de/hsrm/compiler/Klang/visitors/GenASM.java
@@ -357,7 +357,7 @@ public class GenASM implements Visitor<Void> {
     if (isFloatOperation) {
       this.ex.write("    divsd %xmm1, %xmm0\n");
     } else {
-      this.ex.write("    xor %rdx, %rdx\n"); // clear upper part of division
+      this.ex.write("    cqto\n"); // sign extend rax into rdx since we're dealing with signed values
       this.ex.write("    idiv %rbx\n"); // %rax/%rbx, quotient now in %rax
     }
     return null;
@@ -370,7 +370,7 @@ public class GenASM implements Visitor<Void> {
     e.rhs.welcome(this);
     this.ex.write("    movq %rax, %rbx\n");
     this.ex.write("    popq %rax\n");
-    this.ex.write("    xor %rdx, %rdx\n"); // clear upper part of division
+    this.ex.write("    cqto\n"); // sign extend rax into rdx since we're dealing with signed values
     this.ex.write("    idiv %rbx\n"); // %rax/%rbx, remainder now in %rdx
     this.ex.write("    movq %rdx, %rax\n");
     return null;