s390x: add LoadPC to fix compilation error

R=joransiu@ca.ibm.com

Change-Id: Ia8cb93f4d01e252ec6b3b538f795550768db5726
Reviewed-on: https://chromium-review.googlesource.com/c/1362083Reviewed-by: Joran Siu <joransiu@ca.ibm.com>
Commit-Queue: Junliang Yan <jyan@ca.ibm.com>
Cr-Commit-Position: refs/heads/master@{#58033}

src/compiler/backend/s390/code-generator-s390.cc

@@ -1336,11 +1336,7 @@ void CodeGenerator::BailoutIfDeoptimized() {
 void CodeGenerator::GenerateSpeculationPoisonFromCodeStartRegister() {
   Register scratch = r1;
 
-  Label current_pc;
-  __ larl(scratch, &current_pc);
-
-  __ bind(&current_pc);
-  __ SubP(scratch, Operand(__ pc_offset()));
+  __ ComputeCodeStartAddress(scratch);
 
   // Calculate a mask which has all bits set in the normal case, but has all
   // bits cleared if we are speculatively executing the wrong PC.

src/s390/macro-assembler-s390.cc

@@ -4400,6 +4400,12 @@ void TurboAssembler::ComputeCodeStartAddress(Register dst) {
   larl(dst, Operand(-pc_offset() / 2));
 }
 
+void TurboAssembler::LoadPC(Register dst) {
+  Label current_pc;
+  larl(dst, &current_pc);
+  bind(&current_pc);
+}
+
 void TurboAssembler::JumpIfEqual(Register x, int32_t y, Label* dest) {
   Cmp32(x, Operand(y));
   beq(dest);

src/s390/macro-assembler-s390.h

@@ -1006,6 +1006,7 @@ class V8_EXPORT_PRIVATE TurboAssembler : public TurboAssemblerBase {
 
   void ResetSpeculationPoisonRegister();
   void ComputeCodeStartAddress(Register dst);
+  void LoadPC(Register dst);
 
  private:
   static const int kSmiShift = kSmiTagSize + kSmiShiftSize;