MIPSR6: Load full address to t9 when calling PIC code

PIC code requires that full function address is available in t9
upon function entry. We disabled some optimizations that cause
problems since they do not load t9 with full function address.

Bug: 
Change-Id: Ie7987c5e2413db04c59547c33a69696e19db4b34
Reviewed-on: https://chromium-review.googlesource.com/806494Reviewed-by: Miran Karić <miran.karic@mips.com>
Commit-Queue: Ivica Bogosavljevic <ivica.bogosavljevic@mips.com>
Cr-Commit-Position: refs/heads/master@{#49835}

src/mips/macro-assembler-mips.cc

@@ -5127,20 +5127,11 @@ void TurboAssembler::PrepareCallCFunction(int num_reg_arguments,
 void TurboAssembler::CallCFunction(ExternalReference function,
                                    int num_reg_arguments,
                                    int num_double_arguments) {
-  if (IsMipsArchVariant(kMips32r6)) {
-    uint32_t lui_offset, jialc_offset;
-    UnpackTargetAddressUnsigned(Operand(function).immediate(), lui_offset,
-                                jialc_offset);
-    if (MustUseReg(Operand(function).rmode())) {
-      RecordRelocInfo(Operand(function).rmode(), Operand(function).immediate());
-    }
-    lui(t9, lui_offset);
-    CallCFunctionHelper(t9, jialc_offset, num_reg_arguments,
-                        num_double_arguments);
-  } else {
-    li(t9, Operand(function));
-    CallCFunctionHelper(t9, 0, num_reg_arguments, num_double_arguments);
-  }
+  // Linux/MIPS convention demands that register t9 contains
+  // the address of the function being call in case of
+  // Position independent code
+  li(t9, Operand(function));
+  CallCFunctionHelper(t9, 0, num_reg_arguments, num_double_arguments);
 }
 
 void TurboAssembler::CallCFunction(Register function, int num_reg_arguments,
@@ -5197,6 +5188,11 @@ void TurboAssembler::CallCFunctionHelper(Register function_base,
     function_base = t9;
   }
 
+  if (function_offset != 0) {
+    addiu(t9, t9, function_offset);
+    function_offset = 0;
+  }
+
   Call(function_base, function_offset);
 
   int stack_passed_arguments = CalculateStackPassedWords(