[FeedbackVector] Case statements can share a single vector slot

In the fast case, the feedback should be the same across all slots
(like a switch over enum values).

BUG=v8:7045

Change-Id: I2c32f81cda55874ea6fc8d6a18c85d9929cff1bb
Reviewed-on: https://chromium-review.googlesource.com/756701Reviewed-by: Mythri Alle <mythria@chromium.org>
Commit-Queue: Michael Stanton <mvstanton@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49177}

src/interpreter/bytecode-generator.cc

@@ -1382,6 +1382,9 @@ void BytecodeGenerator::VisitSwitchStatement(SwitchStatement* stmt) {
 
   // Keep the switch value in a register until a case matches.
   Register tag = VisitForRegisterValue(stmt->tag());
+  FeedbackSlot slot = clauses->length() > 0
+                          ? feedback_spec()->AddCompareICSlot()
+                          : FeedbackSlot::Invalid();
 
   // Iterate over all cases and create nodes for label comparison.
   for (int i = 0; i < clauses->length(); i++) {
@@ -1395,9 +1398,8 @@ void BytecodeGenerator::VisitSwitchStatement(SwitchStatement* stmt) {
 
     // Perform label comparison as if via '===' with tag.
     VisitForAccumulatorValue(clause->label());
-    builder()->CompareOperation(
-        Token::Value::EQ_STRICT, tag,
-        feedback_index(feedback_spec()->AddCompareICSlot()));
+    builder()->CompareOperation(Token::Value::EQ_STRICT, tag,
+                                feedback_index(slot));
     switch_builder.Case(ToBooleanMode::kAlreadyBoolean, i);
   }
 

test/cctest/interpreter/bytecode_expectations/Switch.golden

@@ -25,7 +25,7 @@ bytecodes: [
                 B(Mov), R(0), R(1),
                 B(JumpIfTrue), U8(11),
                 B(LdaSmi), I8(2),
-                B(TestEqualStrict), R(1), U8(1),
+                B(TestEqualStrict), R(1), U8(0),
                 B(JumpIfTrue), U8(7),
                 B(Jump), U8(8),
   /*   66 S> */ B(LdaSmi), I8(2),
@@ -60,7 +60,7 @@ bytecodes: [
                 B(Mov), R(0), R(1),
                 B(JumpIfTrue), U8(11),
                 B(LdaSmi), I8(2),
-                B(TestEqualStrict), R(1), U8(1),
+                B(TestEqualStrict), R(1), U8(0),
                 B(JumpIfTrue), U8(10),
                 B(Jump), U8(14),
   /*   66 S> */ B(LdaSmi), I8(2),
@@ -97,7 +97,7 @@ bytecodes: [
                 B(Mov), R(0), R(1),
                 B(JumpIfTrue), U8(11),
                 B(LdaSmi), I8(2),
-                B(TestEqualStrict), R(1), U8(1),
+                B(TestEqualStrict), R(1), U8(0),
                 B(JumpIfTrue), U8(8),
                 B(Jump), U8(12),
   /*   66 S> */ B(LdaSmi), I8(2),
@@ -134,7 +134,7 @@ bytecodes: [
                 B(Mov), R(0), R(1),
                 B(JumpIfTrue), U8(11),
                 B(LdaSmi), I8(3),
-                B(TestEqualStrict), R(1), U8(1),
+                B(TestEqualStrict), R(1), U8(0),
                 B(JumpIfTrue), U8(6),
                 B(Jump), U8(6),
   /*   66 S> */ B(Jump), U8(10),
@@ -172,7 +172,7 @@ bytecodes: [
                 B(TestEqualStrict), R(1), U8(0),
                 B(JumpIfTrue), U8(11),
                 B(LdaSmi), I8(3),
-                B(TestEqualStrict), R(1), U8(1),
+                B(TestEqualStrict), R(1), U8(0),
                 B(JumpIfTrue), U8(10),
                 B(Jump), U8(14),
   /*   74 S> */ B(LdaSmi), I8(1),
@@ -313,7 +313,7 @@ bytecodes: [
                 B(Mov), R(0), R(1),
                 B(JumpIfTrue), U8(11),
                 B(LdaSmi), I8(2),
-                B(TestEqualStrict), R(1), U8(1),
+                B(TestEqualStrict), R(1), U8(0),
                 B(JumpIfTrueConstant), U8(0),
                 B(JumpConstant), U8(1),
   /*   68 S> */ B(LdaSmi), I8(2),
@@ -482,14 +482,14 @@ bytecodes: [
                 B(Mov), R(0), R(1),
                 B(JumpIfTrue), U8(11),
                 B(LdaSmi), I8(2),
-                B(TestEqualStrict), R(1), U8(1),
+                B(TestEqualStrict), R(1), U8(0),
                 B(JumpIfTrue), U8(32),
                 B(Jump), U8(34),
   /*   70 S> */ B(Ldar), R(0),
-  /*   79 E> */ B(AddSmi), I8(1), U8(2),
+  /*   79 E> */ B(AddSmi), I8(1), U8(1),
                 B(Star), R(2),
                 B(LdaSmi), I8(2),
-                B(TestEqualStrict), R(2), U8(3),
+                B(TestEqualStrict), R(2), U8(2),
                 B(JumpIfTrue), U8(4),
                 B(Jump), U8(8),
   /*  101 S> */ B(LdaSmi), I8(1),