Deoptimization is easier to diagnose when there is a text reason.

src/mips/lithium-codegen-mips.cc

Index: src/mips/lithium-codegen-mips.cc
diff --git a/src/mips/lithium-codegen-mips.cc b/src/mips/lithium-codegen-mips.cc
index 34e601ccaa386a3eded1aad2b94fefccaf29bf56..6c8f0172f9f7ee8a3b40cef44652b13a9efabf26 100644
--- a/src/mips/lithium-codegen-mips.cc
+++ b/src/mips/lithium-codegen-mips.cc
@@ -5675,6 +5675,8 @@ void LCodeGen::DoDeoptimize(LDeoptimize* instr) {
   if (info()->IsStub() && type == Deoptimizer::EAGER) {
     type = Deoptimizer::LAZY;
   }
+
+  Comment(";;; deoptimize: %s", instr->hydrogen()->reason());
   DeoptimizeIf(al, instr->environment(), type, zero_reg, Operand(zero_reg));
 }