[ia32] Change CEntry calling convention to free kRootRegister

And other related cleanups (additional asserts, use named register
constants instead of the raw register name where appropriate).

Drive-by: Unset kOffHeapTrampolineRegister (it's unused on ia32).

Bug: v8:6666
Change-Id: Id2b94e0b9dbfa5d3bbacc80ec7424d38c4145658
Reviewed-on: https://chromium-review.googlesource.com/1185011
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55328}

src/builtins/ia32/builtins-ia32.cc

@@ -2440,7 +2440,7 @@ void Builtins::Generate_CEntry(MacroAssembler* masm, int result_size,
                                SaveFPRegsMode save_doubles, ArgvMode argv_mode,
                                bool builtin_exit_frame) {
   // eax: number of arguments including receiver
-  // ebx: pointer to C function  (C callee-saved)
+  // edx: pointer to C function
   // ebp: frame pointer  (restored after C call)
   // esp: stack pointer  (restored after C call)
   // esi: current context (C callee-saved)
@@ -2449,6 +2449,16 @@ void Builtins::Generate_CEntry(MacroAssembler* masm, int result_size,
   // If argv_mode == kArgvInRegister:
   // ecx: pointer to the first argument
 
+  STATIC_ASSERT(eax == kRuntimeCallArgCountRegister);
+  STATIC_ASSERT(ecx == kRuntimeCallArgvRegister);
+  STATIC_ASSERT(edx == kRuntimeCallFunctionRegister);
+  STATIC_ASSERT(esi == kContextRegister);
+  STATIC_ASSERT(edi == kJSFunctionRegister);
+
+  DCHECK(!AreAliased(kRuntimeCallArgCountRegister, kRuntimeCallArgvRegister,
+                     kRuntimeCallFunctionRegister, kContextRegister,
+                     kJSFunctionRegister, kRootRegister));
+
   ProfileEntryHookStub::MaybeCallEntryHook(masm);
 
   // Reserve space on the stack for the three arguments passed to the call. If
@@ -2472,7 +2482,7 @@ void Builtins::Generate_CEntry(MacroAssembler* masm, int result_size,
         builtin_exit_frame ? StackFrame::BUILTIN_EXIT : StackFrame::EXIT);
   }
 
-  // ebx: pointer to C function  (C callee-saved)
+  // edx: pointer to C function
   // ebp: frame pointer  (restored after C call)
   // esp: stack pointer  (restored after C call)
   // edi: number of arguments including receiver  (C callee-saved)
@@ -2489,7 +2499,7 @@ void Builtins::Generate_CEntry(MacroAssembler* masm, int result_size,
   __ mov(Operand(esp, 1 * kPointerSize), esi);  // argv.
   __ mov(Operand(esp, 2 * kPointerSize),
          Immediate(ExternalReference::isolate_address(masm->isolate())));
-  __ call(ebx);
+  __ call(kRuntimeCallFunctionRegister);
 
   // Result is in eax or edx:eax - do not destroy these registers!
 

src/ia32/macro-assembler-ia32.cc

@@ -839,8 +839,8 @@ void MacroAssembler::CallRuntime(const Runtime::Function* f,
   // arguments passed in because it is constant. At some point we
   // should remove this need and make the runtime routine entry code
   // smarter.
-  Move(eax, Immediate(num_arguments));
-  mov(ebx, Immediate(ExternalReference::Create(f)));
+  Move(kRuntimeCallArgCountRegister, Immediate(num_arguments));
+  Move(kRuntimeCallFunctionRegister, Immediate(ExternalReference::Create(f)));
   Handle<Code> code =
       CodeFactory::CEntry(isolate(), f->result_size, save_doubles);
   Call(code, RelocInfo::CODE_TARGET);
@@ -853,9 +853,10 @@ void TurboAssembler::CallRuntimeWithCEntry(Runtime::FunctionId fid,
   // arguments passed in because it is constant. At some point we
   // should remove this need and make the runtime routine entry code
   // smarter.
-  Move(eax, Immediate(f->nargs));
-  mov(ebx, Immediate(ExternalReference::Create(f)));
-  DCHECK(!AreAliased(centry, eax, ebx));
+  Move(kRuntimeCallArgCountRegister, Immediate(f->nargs));
+  Move(kRuntimeCallFunctionRegister, Immediate(ExternalReference::Create(f)));
+  DCHECK(!AreAliased(centry, kRuntimeCallArgCountRegister,
+                     kRuntimeCallFunctionRegister));
   add(centry, Immediate(Code::kHeaderSize - kHeapObjectTag));
   Call(centry);
 }
@@ -878,7 +879,7 @@ void MacroAssembler::TailCallRuntime(Runtime::FunctionId fid) {
     // arguments passed in because it is constant. At some point we
     // should remove this need and make the runtime routine entry code
     // smarter.
-    mov(eax, Immediate(function->nargs));
+    Move(kRuntimeCallArgCountRegister, Immediate(function->nargs));
   }
   JumpToExternalReference(ExternalReference::Create(fid));
 }
@@ -886,7 +887,7 @@ void MacroAssembler::TailCallRuntime(Runtime::FunctionId fid) {
 void MacroAssembler::JumpToExternalReference(const ExternalReference& ext,
                                              bool builtin_exit_frame) {
   // Set the entry point and jump to the C entry runtime stub.
-  mov(ebx, Immediate(ext));
+  Move(kRuntimeCallFunctionRegister, Immediate(ext));
   Handle<Code> code = CodeFactory::CEntry(isolate(), 1, kDontSaveFPRegs,
                                           kArgvOnStack, builtin_exit_frame);
   Jump(code, RelocInfo::CODE_TARGET);

src/ia32/macro-assembler-ia32.h

@@ -33,8 +33,11 @@ constexpr Register kJavaScriptCallTargetRegister = kJSFunctionRegister;
 constexpr Register kJavaScriptCallNewTargetRegister = edx;
 constexpr Register kJavaScriptCallExtraArg1Register = ebx;
 
-constexpr Register kOffHeapTrampolineRegister = ecx;
-constexpr Register kRuntimeCallFunctionRegister = ebx;
+// The off-heap trampoline does not need a register on ia32 (it uses a
+// pc-relative call instead).
+constexpr Register kOffHeapTrampolineRegister = no_reg;
+
+constexpr Register kRuntimeCallFunctionRegister = edx;
 constexpr Register kRuntimeCallArgCountRegister = eax;
 constexpr Register kRuntimeCallArgvRegister = ecx;
 constexpr Register kWasmInstanceRegister = esi;