[turbofan] Fix accumulator liveness on suspends

SuspendGenerator needs the accumulator to be live so that it can return
it.

Bug: chromium:806723
Change-Id: Iaa88fce96c36876e3e4256324ca650d475480c10
Reviewed-on: https://chromium-review.googlesource.com/975404Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52147}

src/compiler/bytecode-analysis.cc

@@ -103,7 +103,7 @@ void UpdateInLiveness(Bytecode bytecode, BytecodeLivenessState& in_liveness,
     in_liveness.MarkRegisterLive(accessor.GetRegisterOperand(0).index());
     // Suspend additionally reads and returns the accumulator
     DCHECK(Bytecodes::ReadsAccumulator(bytecode));
-    in_liveness.MarkAccumulatorDead();
+    in_liveness.MarkAccumulatorLive();
     return;
   }
   if (bytecode == Bytecode::kResumeGenerator) {

test/unittests/compiler/bytecode-analysis-unittest.cc

@@ -11,6 +11,7 @@
 #include "src/interpreter/bytecode-label.h"
 #include "src/interpreter/control-flow-builders.h"
 #include "src/objects-inl.h"
+#include "test/unittests/interpreter/bytecode-utils.h"
 #include "test/unittests/test-utils.h"
 
 namespace v8 {
@@ -452,6 +453,53 @@ TEST_F(BytecodeAnalysisTest, KillingLoopInsideLoop) {
   EnsureLivenessMatches(bytecode, expected_liveness);
 }
 
+TEST_F(BytecodeAnalysisTest, SuspendPoint) {
+  interpreter::BytecodeArrayBuilder builder(zone(), 3, 3);
+  std::vector<std::pair<std::string, std::string>> expected_liveness;
+
+  interpreter::Register reg_0(0);
+  interpreter::Register reg_1(1);
+  interpreter::Register reg_gen(2);
+  interpreter::BytecodeJumpTable* gen_jump_table =
+      builder.AllocateJumpTable(1, 0);
+
+  builder.StoreAccumulatorInRegister(reg_gen);
+  expected_liveness.emplace_back("L..L", "L.LL");
+
+  // Note: technically, r0 should be dead here since the resume will write it,
+  // but in practice the bytecode analysis doesn't bother to special case it,
+  // since the generator switch is close to the top of the function anyway.
+  builder.SwitchOnGeneratorState(reg_gen, gen_jump_table);
+  expected_liveness.emplace_back("L.LL", "L.LL");
+
+  builder.StoreAccumulatorInRegister(reg_0);
+  expected_liveness.emplace_back("..LL", "L.LL");
+
+  // Reg 1 is never read, so should be dead.
+  builder.StoreAccumulatorInRegister(reg_1);
+  expected_liveness.emplace_back("L.LL", "L.LL");
+
+  builder.SuspendGenerator(
+      reg_gen, interpreter::BytecodeUtils::NewRegisterList(0, 3), 0);
+  expected_liveness.emplace_back("L.LL", "L.L.");
+
+  builder.Bind(gen_jump_table, 0);
+
+  builder.ResumeGenerator(reg_gen,
+                          interpreter::BytecodeUtils::NewRegisterList(0, 1));
+  expected_liveness.emplace_back("L.L.", "L...");
+
+  builder.LoadAccumulatorWithRegister(reg_0);
+  expected_liveness.emplace_back("L...", "...L");
+
+  builder.Return();
+  expected_liveness.emplace_back("...L", "....");
+
+  Handle<BytecodeArray> bytecode = builder.ToBytecodeArray(isolate());
+
+  EnsureLivenessMatches(bytecode, expected_liveness);
+}
+
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8