AMDGPU: Hack out noinline on functions using LDS globals

[arsenm]

Summary

This is a workaround for clang adding noinline to all functions at
-O0. Previously, we would just add alwaysinline, and the verifier
would complain about having both noinline and alwaysinline. We
currently can't truly codegen this case as a freestanding function, so
override the user forcing noinline.

[rampitec]

LGTM

[arsenm]

c3d3c22a5834ac8afe9618ef9eed5dac370c080d

llvm/lib/Target/AMDGPU/AMDGPUAlwaysInlinePass.cpp

void AMDGPUAlwaysInline::recursivelyVisitUsers(
   while (!Stack.empty()) {
     User *U = Stack.pop_back_val();
     if (!Visited.insert(U).second)
       continue;
 
     if (Instruction *I = dyn_cast<Instruction>(U)) {
       Function *F = I->getParent()->getParent();
       if (!AMDGPU::isEntryFunctionCC(F->getCallingConv())) {
+        // FIXME: This is a horrible hack. We should always respect noinline,
+        // and just let us hit the error when we can't handle this.
+        //
+        // Unfortunately, clang adds noinline to all functions at -O0. We have
+        // to override this here. until that's fixed.
+        F->removeFnAttr(Attribute::NoInline);
+
         FuncsToAlwaysInline.insert(F);
         Stack.push_back(F);
       }
 
       // No need to look at further users, but we do need to inline any callers.
       continue;
     }
 

llvm/test/CodeGen/AMDGPU/force-alwaysinline-lds-global-address.ll

 ; ALL-LABEL: define i32 @recursive_call_lds(i32 %arg0) #0 {
 define i32 @recursive_call_lds(i32 %arg0) {
   %load = load i32, i32 addrspace(3)* @lds0, align 4
   %add = add i32 %arg0, %load
   %call = call i32 @recursive_call_lds(i32 %add)
   ret i32 %call
 }
 
+; Test we don't break the IR and have both alwaysinline and noinline
+; FIXME: We should really not override noinline.
+
+; ALL-LABEL: define i32 @load_lds_simple_noinline() #0 {
+define i32 @load_lds_simple_noinline() noinline {
+  %load = load i32, i32 addrspace(3)* @lds0, align 4
+  ret i32 %load
+}
+
+; ALL-LABEL: define i32 @recursive_call_lds_noinline(i32 %arg0) #0 {
+define i32 @recursive_call_lds_noinline(i32 %arg0) noinline {
+  %load = load i32, i32 addrspace(3)* @lds0, align 4
+  %add = add i32 %arg0, %load
+  %call = call i32 @recursive_call_lds(i32 %add)
+  ret i32 %call
+}
+
 ; ALL: attributes #0 = { alwaysinline }