[CodeGen][i386] Move -mregparm storage earlier and fix Runtime calls (#89707)

When building the Linux kernel for i386, the -mregparm=3 option is
enabled. Crashes were observed in the sanitizer handler functions, and
the problem was found to be mismatched calling convention.

As was fixed in commit c167c0a4dc ("[BuildLibCalls] infer inreg param
attrs from NumRegisterParameters"), call arguments need to be marked as
"in register" when -mregparm is set. Use the same helper developed there
to update the function arguments.

Since CreateRuntimeFunction() is actually part of CodeGenModule, storage
of the -mregparm value is also moved to the constructor, as doing this
in Release() is too late.

Fixes: https://github.com/llvm/llvm-project/issues/89670

clang/lib/CodeGen/CodeGenModule.cpp

@@ -73,6 +73,7 @@
 #include "llvm/TargetParser/RISCVISAInfo.h"
 #include "llvm/TargetParser/Triple.h"
 #include "llvm/TargetParser/X86TargetParser.h"
+#include "llvm/Transforms/Utils/BuildLibCalls.h"
 #include <optional>
 
 using namespace clang;
@@ -442,6 +443,11 @@ CodeGenModule::CodeGenModule(ASTContext &C,
       }
     ModuleNameHash = llvm::getUniqueInternalLinkagePostfix(Path);
   }
+
+  // Record mregparm value now so it is visible through all of codegen.
+  if (Context.getTargetInfo().getTriple().getArch() == llvm::Triple::x86)
+    getModule().addModuleFlag(llvm::Module::Error, "NumRegisterParameters",
+                              CodeGenOpts.NumRegisterParameters);
 }
 
 CodeGenModule::~CodeGenModule() {}
@@ -980,11 +986,6 @@ void CodeGenModule::Release() {
       NMD->addOperand(MD);
   }
 
-  // Record mregparm value now so it is visible through rest of codegen.
-  if (Context.getTargetInfo().getTriple().getArch() == llvm::Triple::x86)
-    getModule().addModuleFlag(llvm::Module::Error, "NumRegisterParameters",
-                              CodeGenOpts.NumRegisterParameters);
-
   if (CodeGenOpts.DwarfVersion) {
     getModule().addModuleFlag(llvm::Module::Max, "Dwarf Version",
                               CodeGenOpts.DwarfVersion);
@@ -4781,6 +4782,10 @@ CodeGenModule::CreateRuntimeFunction(llvm::FunctionType *FTy, StringRef Name,
         }
       }
       setDSOLocal(F);
+      // FIXME: We should use CodeGenModule::SetLLVMFunctionAttributes() instead
+      // of trying to approximate the attributes using the LLVM function
+      // signature. This requires revising the API of CreateRuntimeFunction().
+      markRegisterParameterAttributes(F);
     }
   }