Revert "[llvm-exegesis] Set stack pointer register after starting perf counter (#72489)"

This reverts commit 9eb80ab.

This is causing failures on multiple builders. Pulling it out until I
have time to fix it.

Author: boomanaiden154

llvm/test/tools/llvm-exegesis/X86/latency/subprocess-rsp.s

@@ -19,7 +19,6 @@
 #include "llvm/CodeGen/MachineModuleInfo.h"
 #include "llvm/CodeGen/MachineRegisterInfo.h"
 #include "llvm/CodeGen/TargetInstrInfo.h"
-#include "llvm/CodeGen/TargetLowering.h"
 #include "llvm/CodeGen/TargetPassConfig.h"
 #include "llvm/CodeGen/TargetSubtargetInfo.h"
 #include "llvm/ExecutionEngine/Orc/LLJIT.h"
@@ -61,17 +60,7 @@ static bool generateSnippetSetupCode(
     }
     BBF.addInstructions(ET.setStackRegisterToAuxMem());
   }
-  Register StackPointerRegister = BBF.MF.getSubtarget()
-                                      .getTargetLowering()
-                                      ->getStackPointerRegisterToSaveRestore();
   for (const RegisterValue &RV : RegisterInitialValues) {
-    if (GenerateMemoryInstructions) {
-      // If we're generating memory instructions, don't load in the value for
-      // the register with the stack pointer as it will be used later to finish
-      // the setup.
-      if (RV.Register == StackPointerRegister)
-        continue;
-    }
     // Load a constant in the register.
     const auto SetRegisterCode = ET.setRegTo(*MSI, RV.Register, RV.Value);
     if (SetRegisterCode.empty())
@@ -82,18 +71,6 @@ static bool generateSnippetSetupCode(
 #ifdef HAVE_LIBPFM
     BBF.addInstructions(ET.configurePerfCounter(PERF_EVENT_IOC_RESET, true));
 #endif // HAVE_LIBPFM
-    for (const RegisterValue &RV : RegisterInitialValues) {
-      // Load in the stack register now as we're done using it elsewhere
-      // and need to set the value in preparation for executing the
-      // snippet.
-      if (RV.Register == StackPointerRegister)
-        continue;
-      const auto SetRegisterCode = ET.setRegTo(*MSI, RV.Register, RV.Value);
-      if (SetRegisterCode.empty())
-        IsSnippetSetupComplete = false;
-      BBF.addInstructions(SetRegisterCode);
-      break;
-    }
   }
   return IsSnippetSetupComplete;
 }