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

src/compiler/x64/code-generator-x64.cc

Index: src/compiler/x64/code-generator-x64.cc
diff --git a/src/compiler/x64/code-generator-x64.cc b/src/compiler/x64/code-generator-x64.cc
index a5212cb75ef3389c85012077076569850cd0999f..129302ab02b94ecc25a80166f28edd52e4003cf4 100644
--- a/src/compiler/x64/code-generator-x64.cc
+++ b/src/compiler/x64/code-generator-x64.cc
@@ -4,6 +4,8 @@
 
 #include "src/compiler/code-generator.h"
 
+#include <limits>
+
 #include "src/compilation-info.h"
 #include "src/compiler/code-generator-impl.h"
 #include "src/compiler/gap-resolver.h"
@@ -921,7 +923,7 @@ CodeGenerator::CodeGenResult CodeGenerator::AssembleArchInstruction(
       break;
     }
     case kArchRet:
-      AssembleReturn();
+      AssembleReturn(instr->InputAt(0));
       break;
     case kArchStackPointer:
       __ movq(i.OutputRegister(), rsp);
@@ -2450,8 +2452,7 @@ void CodeGenerator::AssembleConstructFrame() {
   }
 }
 
-
-void CodeGenerator::AssembleReturn() {
+void CodeGenerator::AssembleReturn(InstructionOperand* pop) {
   CallDescriptor* descriptor = linkage()->GetIncomingDescriptor();
 
   // Restore registers.
@@ -2492,10 +2493,23 @@ void CodeGenerator::AssembleReturn() {
       AssembleDeconstructFrame();
     }
   }
-  size_t pop_size = descriptor->StackParameterCount() * kPointerSize;
-  // Might need rcx for scratch if pop_size is too big.
+  // Might need rcx for scratch if pop_size is too big or if there is a variable
+  // pop count.
   DCHECK_EQ(0u, descriptor->CalleeSavedRegisters() & rcx.bit());
-  __ Ret(static_cast<int>(pop_size), rcx);
+  size_t pop_size = descriptor->StackParameterCount() * kPointerSize;
+  X64OperandConverter g(this, nullptr);
+  if (pop->IsImmediate()) {
+    DCHECK_EQ(Constant::kInt32, g.ToConstant(pop).type());
+    pop_size += g.ToConstant(pop).ToInt32() * kPointerSize;
+    CHECK_LT(pop_size, std::numeric_limits<int>::max());
+    __ Ret(static_cast<int>(pop_size), rcx);
+  } else {
+    Register reg = g.ToRegister(pop);
+    __ popq(rcx);
+    CHECK_LT(pop_size, std::numeric_limits<int>::max());
+    __ leaq(rsp, Operand(rsp, reg, times_8, static_cast<int>(pop_size)));
+    __ jmp(rcx);
+  }
 }