[turbofan] Tighter id-ing of exception value in handler blocks

src/compiler/register-allocator.cc

Index: src/compiler/register-allocator.cc
diff --git a/src/compiler/register-allocator.cc b/src/compiler/register-allocator.cc
index 23da999119118176e606992d4e8f41b9be599414..8bf2886d31b4fe60a494af789668a77da8b034e8 100644
--- a/src/compiler/register-allocator.cc
+++ b/src/compiler/register-allocator.cc
@@ -1919,7 +1919,10 @@ void LiveRangeBuilder::ProcessInstructions(const InstructionBlock* block,
         int out_vreg = ConstantOperand::cast(output)->virtual_register();
         live->Remove(out_vreg);
       }
-      if (block->IsHandler() && index == block_start) {
+      if (block->IsHandler() && index == block_start && output->IsAllocated() &&
+          output->IsRegister() &&
+          AllocatedOperand::cast(output)->GetRegister().is(
+              v8::internal::kReturnRegister0)) {
         // The register defined here is blocked from gap start - it is the
         // exception value.
         // TODO(mtrofin): should we explore an explicit opcode for