[CodeGen][GC] Skip function without GC in GCLoweringPass (#84421)

Author: paperchalice

llvm/lib/CodeGen/GCRootLowering.cpp

@@ -81,6 +81,9 @@ class GCMachineCodeAnalysis : public MachineFunctionPass {
 
 PreservedAnalyses GCLoweringPass::run(Function &F,
                                       FunctionAnalysisManager &FAM) {
+  if (!F.hasGC())
+    return PreservedAnalyses::all();
+
   auto &Info = FAM.getResult<GCFunctionAnalysis>(F);
 
   bool Changed = DoLowering(F, Info.getStrategy());

llvm/test/CodeGen/Generic/gc-lowering.ll

@@ -0,0 +1,62 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -S -passes='require<collector-metadata>,function(gc-lowering)' < %s | FileCheck %s
+
+declare ptr @llvm_gc_allocate(i32)
+declare void @llvm_gc_initialize(i32)
+
+declare void @llvm.gcroot(ptr, ptr)
+declare void @llvm.gcwrite(ptr, ptr, ptr)
+
+define i32 @main() gc "shadow-stack" {
+; CHECK-LABEL: define i32 @main() gc "shadow-stack" {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[A:%.*]] = alloca ptr, align 8
+; CHECK-NEXT:    store ptr null, ptr [[A]], align 8
+; CHECK-NEXT:    [[B:%.*]] = alloca ptr, align 8
+; CHECK-NEXT:    store ptr null, ptr [[B]], align 8
+; CHECK-NEXT:    call void @llvm_gc_initialize(i32 1048576)
+; CHECK-NEXT:    call void @llvm.gcroot(ptr [[A]], ptr null)
+; CHECK-NEXT:    [[APTR:%.*]] = call ptr @llvm_gc_allocate(i32 10)
+; CHECK-NEXT:    store ptr [[APTR]], ptr [[A]], align 8
+; CHECK-NEXT:    call void @llvm.gcroot(ptr [[B]], ptr null)
+; CHECK-NEXT:    [[B_UPGRD_1:%.*]] = call ptr @llvm_gc_allocate(i32 8)
+; CHECK-NEXT:    store ptr [[B_UPGRD_1]], ptr [[B]], align 8
+; CHECK-NEXT:    [[B_1:%.*]] = load ptr, ptr [[B]], align 8
+; CHECK-NEXT:    [[A_1:%.*]] = load ptr, ptr [[A]], align 8
+; CHECK-NEXT:    store ptr [[A_1]], ptr [[B_1]], align 8
+; CHECK-NEXT:    ret i32 0
+;
+entry:
+  %A = alloca ptr
+  %B = alloca ptr
+
+  call void @llvm_gc_initialize(i32 1048576)  ; Start with 1MB heap
+
+  ;; ptr A;
+  call void @llvm.gcroot(ptr %A, ptr null)
+
+  ;; A = gcalloc(10);
+  %Aptr = call ptr @llvm_gc_allocate(i32 10)
+  store ptr %Aptr, ptr %A
+
+  ;; ptr B;
+  call void @llvm.gcroot(ptr %B, ptr null)
+
+  ;; B = gcalloc(4);
+  %B.upgrd.1 = call ptr @llvm_gc_allocate(i32 8)
+  store ptr %B.upgrd.1, ptr %B
+
+  ;; *B = A;
+  %B.1 = load ptr, ptr %B
+  %A.1 = load ptr, ptr %A
+  call void @llvm.gcwrite(ptr %A.1, ptr %B.upgrd.1, ptr %B.1)
+
+  ret i32 0
+}
+
+define void @no_gc() {
+; CHECK-LABEL: define void @no_gc() {
+; CHECK-NEXT:    ret void
+;
+  ret void
+}