MIPS: Fix context loading in CheckAccessGlobalProxy

Various failures for MIPS were introduced by the refactoring of
the way frames are marked https://codereview.chromium.org/1696043002.

Problems were caused during context loading in CheckAccessGlobalProxy
* The value of the register at was unintentionally modified.
* Use of branch instruction instead of branch macro resulted in
  a branch instruction in forbidden slot.

BUG=

Review URL: https://codereview.chromium.org/1812463002

Cr-Commit-Position: refs/heads/master@{#34829}

src/mips/macro-assembler-mips.cc

@@ -509,6 +509,7 @@ void MacroAssembler::CheckAccessGlobalProxy(Register holder_reg,
                                             Register scratch,
                                             Label* miss) {
   Label same_contexts;
+  Register temporary = t8;
 
   DCHECK(!holder_reg.is(scratch));
   DCHECK(!holder_reg.is(at));
@@ -521,9 +522,10 @@ void MacroAssembler::CheckAccessGlobalProxy(Register holder_reg,
   mov(at, fp);
   bind(&load_context);
   lw(scratch, MemOperand(at, CommonFrameConstants::kContextOrFrameTypeOffset));
-  JumpIfNotSmi(scratch, &has_context);
+  // Passing temporary register, otherwise JumpIfNotSmi modifies register at.
+  JumpIfNotSmi(scratch, &has_context, temporary);
   lw(at, MemOperand(at, CommonFrameConstants::kCallerFPOffset));
-  b(&load_context);
+  Branch(&load_context);
   bind(&has_context);
 
   // In debug mode, make sure the lexical context is set.

src/mips64/macro-assembler-mips64.cc

@@ -512,6 +512,7 @@ void MacroAssembler::CheckAccessGlobalProxy(Register holder_reg,
                                             Register scratch,
                                             Label* miss) {
   Label same_contexts;
+  Register temporary = t8;
 
   DCHECK(!holder_reg.is(scratch));
   DCHECK(!holder_reg.is(at));
@@ -524,9 +525,10 @@ void MacroAssembler::CheckAccessGlobalProxy(Register holder_reg,
   mov(at, fp);
   bind(&load_context);
   ld(scratch, MemOperand(at, CommonFrameConstants::kContextOrFrameTypeOffset));
-  JumpIfNotSmi(scratch, &has_context);
+  // Passing temporary register, otherwise JumpIfNotSmi modifies register at.
+  JumpIfNotSmi(scratch, &has_context, temporary);
   ld(at, MemOperand(at, CommonFrameConstants::kCallerFPOffset));
-  b(&load_context);
+  Branch(&load_context);
   bind(&has_context);
 
   // In debug mode, make sure the lexical context is set.