PPC/s390: [turbofan] Refactor the compare-zero folding in instruction selector.

Port 9b308dca

R=jarin@chromium.org, joransiu@ca.ibm.com, jyan@ca.ibm.com, bjaideep@ca.ibm.com, michael_dawson@ca.ibm.com, mbrandy@us.ibm.com
BUG=

Review-Url: https://codereview.chromium.org/2470043006
Cr-Commit-Position: refs/heads/master@{#40774}

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

@@ -1602,21 +1602,22 @@ void VisitFloat64Compare(InstructionSelector* selector, Node* node,
 void VisitWordCompareZero(InstructionSelector* selector, Node* user,
                           Node* value, InstructionCode opcode,
                           FlagsContinuation* cont) {
-  while (selector->CanCover(user, value)) {
-    switch (value->opcode()) {
-      case IrOpcode::kWord32Equal: {
-        // Combine with comparisons against 0 by simply inverting the
-        // continuation.
+  // Try to combine with comparisons against 0 by simply inverting the branch.
+  while (value->opcode() == IrOpcode::kWord32Equal &&
+         selector->CanCover(user, value)) {
     Int32BinopMatcher m(value);
-        if (m.right().Is(0)) {
+    if (!m.right().Is(0)) break;
+
     user = value;
     value = m.left().node();
     cont->Negate();
-          continue;
   }
+
+  if (selector->CanCover(user, value)) {
+    switch (value->opcode()) {
+      case IrOpcode::kWord32Equal:
         cont->OverwriteAndNegateIfEqual(kEqual);
         return VisitWord32Compare(selector, value, cont);
-      }
       case IrOpcode::kInt32LessThan:
         cont->OverwriteAndNegateIfEqual(kSignedLessThan);
         return VisitWord32Compare(selector, value, cont);
@@ -1738,7 +1739,6 @@ void VisitWordCompareZero(InstructionSelector* selector, Node* user,
       default:
         break;
     }
-    break;
   }
 
   // Branch could not be combined with a compare, emit compare against 0.

src/compiler/s390/instruction-selector-s390.cc

@@ -1607,21 +1607,22 @@ void VisitFloat64Compare(InstructionSelector* selector, Node* node,
 void VisitWordCompareZero(InstructionSelector* selector, Node* user,
                           Node* value, InstructionCode opcode,
                           FlagsContinuation* cont) {
-  while (selector->CanCover(user, value)) {
-    switch (value->opcode()) {
-      case IrOpcode::kWord32Equal: {
-        // Combine with comparisons against 0 by simply inverting the
-        // continuation.
+  // Try to combine with comparisons against 0 by simply inverting the branch.
+  while (value->opcode() == IrOpcode::kWord32Equal &&
+         selector->CanCover(user, value)) {
     Int32BinopMatcher m(value);
-        if (m.right().Is(0)) {
+    if (!m.right().Is(0)) break;
+
     user = value;
     value = m.left().node();
     cont->Negate();
-          continue;
   }
+
+  if (selector->CanCover(user, value)) {
+    switch (value->opcode()) {
+      case IrOpcode::kWord32Equal:
         cont->OverwriteAndNegateIfEqual(kEqual);
         return VisitWord32Compare(selector, value, cont);
-      }
       case IrOpcode::kInt32LessThan:
         cont->OverwriteAndNegateIfEqual(kSignedLessThan);
         return VisitWord32Compare(selector, value, cont);
@@ -1740,7 +1741,6 @@ void VisitWordCompareZero(InstructionSelector* selector, Node* user,
       default:
         break;
     }
-    break;
   }
 
   // Branch could not be combined with a compare, emit compare against 0.