Rollback trunk to 3.21.15.

src/arm/lithium-arm.cc

Index: src/arm/lithium-arm.cc
diff --git a/src/arm/lithium-arm.cc b/src/arm/lithium-arm.cc
index 7f504ea4ad4452d7da59d63bb192172fd021abee..59a8818ac6b6b2e02f2c22b97b789771fea12d5e 100644
--- a/src/arm/lithium-arm.cc
+++ b/src/arm/lithium-arm.cc
@@ -1883,9 +1883,11 @@ 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);
 }