Rollback trunk to 3.21.15.

src/mips/lithium-mips.cc

Index: src/mips/lithium-mips.cc
diff --git a/src/mips/lithium-mips.cc b/src/mips/lithium-mips.cc
index 38134f4691c73bda88a81c916c1047265221bf9a..4dc80226f295efd8850efa45c319867cffb4ff90 100644
--- a/src/mips/lithium-mips.cc
+++ b/src/mips/lithium-mips.cc
@@ -1783,9 +1783,11 @@ LInstruction* LChunkBuilder::DoDateField(HDateField* instr) {
 
 LInstruction* LChunkBuilder::DoSeqStringSetChar(HSeqStringSetChar* instr) {
   LOperand* string = UseRegister(instr->string());
-  LOperand* index = UseRegisterOrConstant(instr->index());
-  LOperand* value = UseRegister(instr->value());
-  return new(zone()) LSeqStringSetChar(instr->encoding(), string, index, value);
+  LOperand* index = UseRegister(instr->index());
+  LOperand* value = UseTempRegister(instr->value());
+  LSeqStringSetChar* result =
+      new(zone()) LSeqStringSetChar(instr->encoding(), string, index, value);
+  return DefineAsRegister(result);
 }