[instruction-selector-x64] Fix bug in instruction selector

A node short-cutting optimization was not updating uses correctly. This
fix makes sure that there are no other users of the node, thus making the
use update unnecessary.

This fix might have negative performance implications.

Change-Id: Ie9bd23caf4434eb2137e111dc5e7c143fd97521c
Reviewed-on: https://chromium-review.googlesource.com/c/1299019
Commit-Queue: Sigurd Schneider <sigurds@chromium.org>
Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57001}

src/compiler/x64/instruction-selector-x64.cc

@@ -1671,10 +1671,15 @@ void VisitWordCompare(InstructionSelector* selector, Node* node,
   // The 32-bit comparisons automatically truncate Word64
   // values to Word32 range, no need to do that explicitly.
   if (opcode == kX64Cmp32 || opcode == kX64Test32) {
-    while (left->opcode() == IrOpcode::kTruncateInt64ToInt32) {
+    if (left->opcode() == IrOpcode::kTruncateInt64ToInt32 &&
+        selector->CanCover(node, left) &&
+        selector->CanCover(left, left->InputAt(0))) {
       left = left->InputAt(0);
     }
-    while (right->opcode() == IrOpcode::kTruncateInt64ToInt32) {
+
+    if (right->opcode() == IrOpcode::kTruncateInt64ToInt32 &&
+        selector->CanCover(node, right) &&
+        selector->CanCover(right, right->InputAt(0))) {
       right = right->InputAt(0);
     }
   }