[AMDGPU] Internalize non-kernel symbols

Since we have no call support and late linking we can produce code
only for used symbols. This saves compilation time, size of the final
executable, and size of any intermediate dumps.

Run Internalize pass early in the opt pipeline followed by global
DCE pass. To enable it RT can pass -amdgpu-internalize-symbols option.

Differential Revision: https://reviews.llvm.org/D29214

llvm-svn: 293549

llvm/lib/Target/AMDGPU/AMDGPUTargetMachine.cpp

@@ -84,6 +84,13 @@ static cl::opt<bool> ScalarizeGlobal(
   cl::init(false),
   cl::Hidden);
 
+// Option to run internalize pass.
+static cl::opt<bool> InternalizeSymbols(
+  "amdgpu-internalize-symbols",
+  cl::desc("Enable elimination of non-kernel functions and unused globals"),
+  cl::init(false),
+  cl::Hidden);
+
 extern "C" void LLVMInitializeAMDGPUTarget() {
   // Register the target
   RegisterTargetMachine<R600TargetMachine> X(getTheAMDGPUTarget());
@@ -207,11 +214,35 @@ StringRef AMDGPUTargetMachine::getFeatureString(const Function &F) const {
 }
 
 void AMDGPUTargetMachine::adjustPassManager(PassManagerBuilder &Builder) {
+  bool Internalize = InternalizeSymbols &&
+                     (getOptLevel() > CodeGenOpt::None) &&
+                     (getTargetTriple().getArch() == Triple::amdgcn);
   Builder.addExtension(
     PassManagerBuilder::EP_ModuleOptimizerEarly,
-    [&](const PassManagerBuilder &, legacy::PassManagerBase &PM) {
+    [Internalize](const PassManagerBuilder &, legacy::PassManagerBase &PM) {
       PM.add(createAMDGPUUnifyMetadataPass());
-    });
+      if (Internalize) {
+        PM.add(createInternalizePass([=](const GlobalValue &GV) -> bool {
+          if (const Function *F = dyn_cast<Function>(&GV)) {
+            if (F->isDeclaration())
+                return true;
+            switch (F->getCallingConv()) {
+            default:
+              return false;
+            case CallingConv::AMDGPU_VS:
+            case CallingConv::AMDGPU_GS:
+            case CallingConv::AMDGPU_PS:
+            case CallingConv::AMDGPU_CS:
+            case CallingConv::AMDGPU_KERNEL:
+            case CallingConv::SPIR_KERNEL:
+              return true;
+            }
+          }
+          return !GV.use_empty();
+        }));
+        PM.add(createGlobalDCEPass());
+      }
+  });
 }
 
 //===----------------------------------------------------------------------===//

llvm/test/CodeGen/AMDGPU/internalize.ll

@@ -0,0 +1,35 @@
+; RUN: opt -O1 -S -mtriple=amdgcn-unknown-amdhsa -amdgpu-internalize-symbols < %s | FileCheck %s
+; CHECK-NOT: unused
+; CHECK-NOT: foo_used
+; CHECK: gvar_used
+; CHECK: main_kernel
+
+@gvar_unused = addrspace(1) global i32 undef, align 4
+@gvar_used = addrspace(1) global i32 undef, align 4
+
+; Function Attrs: alwaysinline nounwind
+define void @foo_unused(i32 addrspace(1)* %out) local_unnamed_addr #1 {
+entry:
+  store i32 1, i32 addrspace(1)* %out
+  ret void
+}
+
+; Function Attrs: alwaysinline nounwind
+define void @foo_used(i32 addrspace(1)* %out, i32 %tid) local_unnamed_addr #1 {
+entry:
+  store i32 %tid, i32 addrspace(1)* %out
+  ret void
+}
+
+define amdgpu_kernel void @main_kernel() {
+entry:
+  %tid = call i32 @llvm.amdgcn.workitem.id.x()
+  tail call void @foo_used(i32 addrspace(1)* @gvar_used, i32 %tid) nounwind
+  ret void
+}
+
+declare i32 @llvm.amdgcn.workitem.id.x() #0
+
+attributes #0 = { nounwind readnone }
+
+attributes #1 = { alwaysinline nounwind }