Rollback trunk to 3.21.15.

src/arm/lithium-codegen-arm.cc

Index: src/arm/lithium-codegen-arm.cc
diff --git a/src/arm/lithium-codegen-arm.cc b/src/arm/lithium-codegen-arm.cc
index b7fc3b6055c67704f1065e3f232f039aa52bb745..7f65023ed00827e58d8629af5a563327bd92f9d5 100644
--- a/src/arm/lithium-codegen-arm.cc
+++ b/src/arm/lithium-codegen-arm.cc
@@ -1975,42 +1975,32 @@ void LCodeGen::DoDateField(LDateField* instr) {
 
 void LCodeGen::DoSeqStringSetChar(LSeqStringSetChar* instr) {
   Register string = ToRegister(instr->string());
-  LOperand* index_op = instr->index();
+  Register index = ToRegister(instr->index());
   Register value = ToRegister(instr->value());
-  Register scratch = scratch0();
   String::Encoding encoding = instr->encoding();
 
   if (FLAG_debug_code) {
-    __ ldr(scratch, FieldMemOperand(string, HeapObject::kMapOffset));
-    __ ldrb(scratch, FieldMemOperand(scratch, Map::kInstanceTypeOffset));
+    __ ldr(ip, FieldMemOperand(string, HeapObject::kMapOffset));
+    __ ldrb(ip, FieldMemOperand(ip, Map::kInstanceTypeOffset));
 
-    __ and_(scratch, scratch,
-            Operand(kStringRepresentationMask | kStringEncodingMask));
+    __ and_(ip, ip, Operand(kStringRepresentationMask | kStringEncodingMask));
     static const uint32_t one_byte_seq_type = kSeqStringTag | kOneByteStringTag;
     static const uint32_t two_byte_seq_type = kSeqStringTag | kTwoByteStringTag;
-    __ cmp(scratch, Operand(encoding == String::ONE_BYTE_ENCODING
-                            ? one_byte_seq_type : two_byte_seq_type));
+    __ cmp(ip, Operand(encoding == String::ONE_BYTE_ENCODING
+                           ? one_byte_seq_type : two_byte_seq_type));
     __ Check(eq, kUnexpectedStringType);
   }
 
-  if (index_op->IsConstantOperand()) {
-    int constant_index = ToInteger32(LConstantOperand::cast(index_op));
-    if (encoding == String::ONE_BYTE_ENCODING) {
-      __ strb(value,
-              FieldMemOperand(string, SeqString::kHeaderSize + constant_index));
-    } else {
-      __ strh(value,
-          FieldMemOperand(string, SeqString::kHeaderSize + constant_index * 2));
-    }
+  __ add(ip,
+         string,
+         Operand(SeqString::kHeaderSize - kHeapObjectTag));
+  if (encoding == String::ONE_BYTE_ENCODING) {
+    __ strb(value, MemOperand(ip, index));
   } else {
-    Register index = ToRegister(index_op);
-    if (encoding == String::ONE_BYTE_ENCODING) {
-      __ add(scratch, string, Operand(index));
-      __ strb(value, FieldMemOperand(scratch, SeqString::kHeaderSize));
-    } else {
-      __ add(scratch, string, Operand(index, LSL, 1));
-      __ strh(value, FieldMemOperand(scratch, SeqString::kHeaderSize));
-    }
+    // MemOperand with ip as the base register is not allowed for strh, so
+    // we do the address calculation explicitly.
+    __ add(ip, ip, Operand(index, LSL, 1));
+    __ strh(value, MemOperand(ip));
   }
 }