[turbofan] Fixes the code generation for branches on x64 when the condition is Word64Equal.

Before:

REX.W cmpq r9,r8
setzl r8l
movzxbl r8,r8
REX.W cmpq r8,0x0
jz 185

After:

REX.W cmpq r9,r8
jnz 149

Review URL: https://codereview.chromium.org/1677503002

Cr-Commit-Position: refs/heads/master@{#33784}

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

@@ -1431,24 +1431,24 @@ void InstructionSelector::VisitBranch(Node* branch, BasicBlock* tbranch,
 
   FlagsContinuation cont(kNotEqual, tbranch, fbranch);
 
-  // Try to combine with comparisons against 0 by simply inverting the branch.
-  while (CanCover(user, value) && value->opcode() == IrOpcode::kWord32Equal) {
-    Int32BinopMatcher m(value);
-    if (m.right().Is(0)) {
-      user = value;
-      value = m.left().node();
-      cont.Negate();
-    } else {
-      break;
-    }
-  }
-
   // Try to combine the branch with a comparison.
-  if (CanCover(user, value)) {
+  while (CanCover(user, value)) {
     switch (value->opcode()) {
       case IrOpcode::kWord32Equal:
+      case IrOpcode::kWord64Equal: {
+        Int64BinopMatcher m(value);
+        if (m.right().Is(0)) {
+          user = value;
+          value = m.left().node();
+          cont.Negate();
+          continue;
+        }
         cont.OverwriteAndNegateIfEqual(kEqual);
-        return VisitWordCompare(this, value, kX64Cmp32, &cont);
+        return VisitWordCompare(
+            this, value,
+            value->opcode() == IrOpcode::kWord64Equal ? kX64Cmp : kX64Cmp32,
+            &cont);
+      }
       case IrOpcode::kInt32LessThan:
         cont.OverwriteAndNegateIfEqual(kSignedLessThan);
         return VisitWordCompare(this, value, kX64Cmp32, &cont);
@@ -1461,27 +1461,6 @@ void InstructionSelector::VisitBranch(Node* branch, BasicBlock* tbranch,
       case IrOpcode::kUint32LessThanOrEqual:
         cont.OverwriteAndNegateIfEqual(kUnsignedLessThanOrEqual);
         return VisitWordCompare(this, value, kX64Cmp32, &cont);
-      case IrOpcode::kWord64Equal: {
-        cont.OverwriteAndNegateIfEqual(kEqual);
-        Int64BinopMatcher m(value);
-        if (m.right().Is(0)) {
-          // Try to combine the branch with a comparison.
-          Node* const user = m.node();
-          Node* const value = m.left().node();
-          if (CanCover(user, value)) {
-            switch (value->opcode()) {
-              case IrOpcode::kInt64Sub:
-                return VisitWord64Compare(this, value, &cont);
-              case IrOpcode::kWord64And:
-                return VisitWordCompare(this, value, kX64Test, &cont);
-              default:
-                break;
-            }
-          }
-          return VisitCompareZero(this, value, kX64Cmp, &cont);
-        }
-        return VisitWord64Compare(this, value, &cont);
-      }
       case IrOpcode::kInt64LessThan:
         cont.OverwriteAndNegateIfEqual(kSignedLessThan);
         return VisitWord64Compare(this, value, &cont);
@@ -1551,9 +1530,16 @@ void InstructionSelector::VisitBranch(Node* branch, BasicBlock* tbranch,
         return VisitWordCompare(this, value, kX64Test32, &cont);
       case IrOpcode::kWord64And:
         return VisitWordCompare(this, value, kX64Test, &cont);
+      case IrOpcode::kLoad:
+        if (LoadRepresentationOf(value->op()).representation() ==
+            MachineRepresentation::kWord64) {
+          return VisitCompareZero(this, value, kX64Cmp, &cont);
+        }
+        break;
       default:
         break;
     }
+    break;
   }
 
   // Branch could not be combined with a compare, emit compare against 0.