[X86] Add NumRegisterParameters Module Flag

[mkuper]

So, I remember back when I implemented the MCU ABI rnk and I discussed this, and didn't really reach a definitive conclusion.

This would make -mregparm behavior match GCC, but would be an ABI break for clang.
You may want to surface this on llvm-dev, and check that doesn't come as a surprise to anyone.

[mkuper]

Another issue is that we need to serialize this as part of the IR for the function.
Since we don't use inreg attributes, it needs to either be a part of the calling convention (although we currently have no way to parametrize the CC, I think), or a function attribute.

[rnk]

This seems like a good use case for module flags, actually. Check out Module::ModFlagBehavior::Error in particular.

[mkuper]

I'm not sure. It basically comes down to - do we want to ever be able to combine (say, link) -mregparm code with non-mregparm code.

For the MCU this was a non-issue, because the answer is always no.

[niravd]

Change propagate to use subtarget features

[niravd]

Change to llvm module flag

[jlebar]

test/CodeGenCUDA/flush-denormals.cu

21

Hm, this is a bummer, but I don't immediately see a better way to do it.

[rnk]

lib/CodeGen/CodeGenModule.cpp

421

I'd like this to be conditional on NumRegisterParameters being non-zero, so that it doesn't pollute the vast majority of modules that don't use -mregparm. I think you will get the right LTO diagnostic behavior if you use llvm::Module::Require instead of Error here.

test/CodeGenCUDA/flush-denormals.cu

21

I think this can be removed if the module flag is made conditional.

[niravd]

lib/CodeGen/CodeGenModule.cpp

421

My understanding is that Require only checks the post-linking values, so we'd not error when linking regparm 0 with regparm N.

That said, it'd be easy enough to restrict emitting the module flag to target that actually depend on it, i.e. X86-32. That would get us 90% of the way.

[rnk]

lgtm

lib/CodeGen/CodeGenModule.cpp

421

Hm, nevermind then. Let's go with what you have.

test/CodeGen/pr3997.c

5

Probably worth checking that this calls llvm.memcpy without any inreg attributes.

10

Probably worth CHECKs for whatever we do for this today.

[yaron.keren]

Most other module flags are added at CodeGenModule::Release(). For consistency, could this code be in CodeGenModule::Release() as well?

[yaron.keren]

No intention of any major work intended... just moved the code (locally) to Release and regression tests were still passing.

I must be missing something - isn't the module flag is used in X86ISelLowering which is called after CodeGenModule::Release() is done?

lib/CodeGen/CodeGenModule.cpp

void CodeGenModule::Release() {
   emitLLVMUsed();
   if (SanStats)
     SanStats->finish();
 
   if (CodeGenOpts.Autolink &&
       (Context.getLangOpts().Modules || !LinkerOptionsMetadata.empty())) {
     EmitModuleLinkOptions();
   }
+
+  // Record mregparm value.
+  getModule().addModuleFlag(llvm::Module::Error, "NumRegisterParameters",
+                            CodeGenOpts.NumRegisterParameters);
+
   if (CodeGenOpts.DwarfVersion) {
     // We actually want the latest version when there are conflicts.
     // We can change from Warning to Latest if such mode is supported.
     getModule().addModuleFlag(llvm::Module::Warning, "Dwarf Version",
                               CodeGenOpts.DwarfVersion);
   }
   if (CodeGenOpts.EmitCodeView) {
     // Indicate that we want CodeView in the metadata.

lib/CodeGen/MicrosoftCXXABI.cpp

llvm::Constant *getThrowFn() {
     // which describes the exception.
     llvm::Type *Args[] = {CGM.Int8PtrTy, getThrowInfoType()->getPointerTo()};
     llvm::FunctionType *FTy =
         llvm::FunctionType::get(CGM.VoidTy, Args, /*IsVarArgs=*/false);
     auto *Fn = cast<llvm::Function>(
         CGM.CreateRuntimeFunction(FTy, "_CxxThrowException"));
     // _CxxThrowException is stdcall on 32-bit x86 platforms.
     if (CGM.getTarget().getTriple().getArch() == llvm::Triple::x86)
-      Fn->setCallingConv(llvm::CallingConv::X86_StdCall);
+      Fn->setCallingConv(llvm::CallingConv::X86_LibStdCall);
     return Fn;
   }
 
   llvm::Function *getAddrOfCXXCtorClosure(const CXXConstructorDecl *CD,
                                           CXXCtorType CT);
 
   llvm::Constant *getCatchableType(QualType T,
                                    uint32_t NVOffset = 0,

test/CodeGen/pr3997.c

+// RUN: %clang_cc1 %s -triple i386-unknown-linux-gnu -mregparm 3 -emit-llvm -o - | FileCheck %s
+
+void *memcpy(void *dest, const void *src, unsigned int n);
+
+void use_builtin_memcpy(void *dest, const void *src, unsigned int n) {
+  __builtin_memcpy(dest, src, n);
+}
+
+void use_memcpy(void *dest, const void *src, unsigned int n) {
+  memcpy(dest, src, n);
+}
+
+//CHECK: !{i32 1, !"NumRegisterParameters", i32 3}

test/CodeGenCUDA/flush-denormals.cu

 // or absence of -fcuda-flush-denormals-to-zero in a module flag.
 
 // CHECK-LABEL: define void @foo() #0
 extern "C" __device__ void foo() {}
 
 // FTZ: attributes #0 = {{.*}} "nvptx-f32ftz"="true"
 // NOFTZ-NOT: attributes #0 = {{.*}} "nvptx-f32ftz"
 
-// FTZ:!llvm.module.flags = !{[[MODFLAG:![0-9]+]]}
+// FTZ:!llvm.module.flags = !{!0, [[MODFLAG:![0-9]+]]}
 // FTZ:[[MODFLAG]] = !{i32 4, !"nvvm-reflect-ftz", i32 1}
 
-// NOFTZ:!llvm.module.flags = !{[[MODFLAG:![0-9]+]]}
+// NOFTZ:!llvm.module.flags = !{!0, [[MODFLAG:![0-9]+]]}
 // NOFTZ:[[MODFLAG]] = !{i32 4, !"nvvm-reflect-ftz", i32 0}

test/CodeGenCXX/strict-vtable-pointers.cpp

 // CHECK-DTORS: call i8* @llvm.invariant.group.barrier(
 // CHECK-DTORS-LABEL: {{^}}}
 
 // CHECK-DTORS-LABEL: define linkonce_odr void @_ZN14DynamicDerivedD2Ev
 // CHECK-DTORS-NOT: call i8* @llvm.invariant.group.barrier(
 // CHECK-DTORS-LABEL: {{^}}}
 
 
-// CHECK-LINK-REQ: !llvm.module.flags = !{![[FIRST:.*]], ![[SEC:.*]]{{.*}}}
+// CHECK-LINK-REQ: !llvm.module.flags = !{!0, ![[FIRST:.*]], ![[SEC:.*]]{{.*}}}
 
 // CHECK-LINK-REQ: ![[FIRST]] = !{i32 1, !"StrictVTablePointers", i32 1}
 // CHECK-LINK-REQ: ![[SEC]] = !{i32 3, !"StrictVTablePointersRequirement", ![[META:.*]]}
 // CHECK-LINK-REQ: ![[META]] = !{!"StrictVTablePointers", i32 1}
-

test/Headers/altivec-header.c

 // RUN: %clang_cc1 -triple powerpc64-unknown-unknown -faltivec -ffreestanding -emit-llvm -o - %s | FileCheck %s
 // RUN: %clang_cc1 -triple powerpc64-unknown-unknown -faltivec -ffreestanding -emit-llvm -fno-lax-vector-conversions -o - %s | FileCheck %s
 // RUN: %clang_cc1 -triple powerpc64-unknown-unknown -faltivec -ffreestanding -emit-llvm -x c++ -o - %s | FileCheck %s
 
 #include <altivec.h>
 
 // Verify that simply including <altivec.h> does not generate any code
 // (i.e. all inline routines in the header are marked "static")
 
 // CHECK: target triple = "powerpc64-
 // CHECK-NEXT: {{^$}}
-// CHECK-NEXT: llvm.ident
+// CHECK-NEXT: {{llvm\..*}}