Properly handle always taken conditions in cmov

Change-Id: I6dec06936cb12f2d6da69c1f147bea344c32cf73
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3629129Reviewed-by: Clemens Backes <clemensb@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Commit-Queue: Stephen Röttger <sroettger@google.com>
Cr-Commit-Position: refs/heads/main@{#80370}

src/codegen/x64/assembler-x64.cc

@@ -1070,6 +1070,7 @@ void Assembler::cdq() {
 void Assembler::cmovq(Condition cc, Register dst, Register src) {
   if (cc == always) {
     movq(dst, src);
+    return;
   } else if (cc == never) {
     return;
   }
@@ -1087,6 +1088,7 @@ void Assembler::cmovq(Condition cc, Register dst, Register src) {
 void Assembler::cmovq(Condition cc, Register dst, Operand src) {
   if (cc == always) {
     movq(dst, src);
+    return;
   } else if (cc == never) {
     return;
   }
@@ -1102,6 +1104,7 @@ void Assembler::cmovq(Condition cc, Register dst, Operand src) {
 void Assembler::cmovl(Condition cc, Register dst, Register src) {
   if (cc == always) {
     movl(dst, src);
+    return;
   } else if (cc == never) {
     return;
   }
@@ -1117,6 +1120,7 @@ void Assembler::cmovl(Condition cc, Register dst, Register src) {
 void Assembler::cmovl(Condition cc, Register dst, Operand src) {
   if (cc == always) {
     movl(dst, src);
+    return;
   } else if (cc == never) {
     return;
   }