[turbofan] Support variable size argument popping in TF-generated functions

src/compiler/ia32/code-generator-ia32.cc

Index: src/compiler/ia32/code-generator-ia32.cc
diff --git a/src/compiler/ia32/code-generator-ia32.cc b/src/compiler/ia32/code-generator-ia32.cc
index 2b8cf08cb71e81eb286fbed3009e2a33484fb48d..2e54e2a6341654c0e5bee142b65cba715c7c34b6 100644
--- a/src/compiler/ia32/code-generator-ia32.cc
+++ b/src/compiler/ia32/code-generator-ia32.cc
@@ -649,7 +649,7 @@ CodeGenerator::CodeGenResult CodeGenerator::AssembleArchInstruction(
       break;
     }
     case kArchRet:
-      AssembleReturn();
+      AssembleReturn(instr->InputAt(0));
       break;
     case kArchStackPointer:
       __ mov(i.OutputRegister(), esp);
@@ -1981,8 +1981,7 @@ void CodeGenerator::AssembleConstructFrame() {
   }
 }
 
-
-void CodeGenerator::AssembleReturn() {
+void CodeGenerator::AssembleReturn(InstructionOperand* pop) {
   CallDescriptor* descriptor = linkage()->GetIncomingDescriptor();
 
   const RegList saves = descriptor->CalleeSavedRegisters();
@@ -1994,22 +1993,41 @@ void CodeGenerator::AssembleReturn() {
     }
   }
 
+  // Might need ecx for scratch if pop_size is too big or if there is a variable
+  // pop count.
+  DCHECK_EQ(0u, descriptor->CalleeSavedRegisters() & ecx.bit());
+  size_t pop_size = descriptor->StackParameterCount() * kPointerSize;
+  IA32OperandConverter g(this, nullptr);
   if (descriptor->IsCFunctionCall()) {
     AssembleDeconstructFrame();
   } else if (frame_access_state()->has_frame()) {
-    // Canonicalize JSFunction return sites for now.
-    if (return_label_.is_bound()) {
-      __ jmp(&return_label_);
-      return;
+    // Canonicalize JSFunction return sites for now if they always have the same
+    // number of return args.
+    if (pop->IsImmediate() && g.ToConstant(pop).ToInt32() == 0) {
+      if (return_label_.is_bound()) {
+        __ jmp(&return_label_);
+        return;
+      } else {
+        __ bind(&return_label_);
+        AssembleDeconstructFrame();
+      }
     } else {
-      __ bind(&return_label_);
       AssembleDeconstructFrame();
     }
   }
-  size_t pop_size = descriptor->StackParameterCount() * kPointerSize;
-  // Might need ecx for scratch if pop_size is too big.
+  DCHECK_EQ(0u, descriptor->CalleeSavedRegisters() & edx.bit());
   DCHECK_EQ(0u, descriptor->CalleeSavedRegisters() & ecx.bit());
-  __ Ret(static_cast<int>(pop_size), ecx);
+  if (pop->IsImmediate()) {
+    DCHECK_EQ(Constant::kInt32, g.ToConstant(pop).type());
+    pop_size += g.ToConstant(pop).ToInt32() * kPointerSize;
+    __ Ret(static_cast<int>(pop_size), ecx);
+  } else {
+    Register pop_reg = g.ToRegister(pop);
+    Register scratch_reg = pop_reg.is(ecx) ? edx : ecx;
+    __ pop(scratch_reg);
+    __ lea(esp, Operand(esp, pop_reg, times_4, static_cast<int>(pop_size)));
+    __ jmp(scratch_reg);
+  }
 }