Add tests, clarify comments

Author: usha1830

llvm/lib/Transforms/IPO/FunctionAttrs.cpp

@@ -2472,12 +2472,12 @@ PreservedAnalyses NoRecurseLTOInferencePass::run(Module &M,
 
   for (LazyCallGraph::RefSCC &RC : CG.postorder_ref_sccs()) {
     // Skip any RefSCC that is part of a call cycle. A RefSCC containing more
-    // than one SCC indicates a recursive relationship, which could involve
-    // direct or indirect calls.
+    // than one SCC indicates a recursive relationship involving indirect calls.
     if (RC.size() > 1)
       continue;
 
-    // A single-SCC RefSCC could still be a self-loop.
+    // RefSCC contains a single-SCC. SCC size > 1 indicates mutually recursive
+    // functions. Ex: foo1 -> foo2 -> foo3 -> foo1.
     LazyCallGraph::SCC &S = *RC.begin();
     if (S.size() > 1)
       continue;

llvm/test/Transforms/FunctionAttrs/norecurse_lto.ll

@@ -0,0 +1,69 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --check-attributes --check-globals all --version 5
+; RUN: opt < %s -passes=norecurse-lto-inference -S | FileCheck %s
+
+; This test includes a call graph which has a recursive function(foo2) which
+; calls a non-recursive internal function (foo3) satisfying the norecurse
+; attribute criteria.
+
+
+define internal void @foo3() {
+; CHECK: Function Attrs: norecurse
+; CHECK-LABEL: define internal void @foo3(
+; CHECK-SAME: ) #[[ATTR0:[0-9]+]] {
+; CHECK-NEXT:    ret void
+;
+  ret void
+}
+
+define internal i32 @foo2(i32 %accum, i32 %n) {
+; CHECK-LABEL: define internal i32 @foo2(
+; CHECK-SAME: i32 [[ACCUM:%.*]], i32 [[N:%.*]]) {
+; CHECK-NEXT:  [[ENTRY:.*]]:
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i32 [[N]], 0
+; CHECK-NEXT:    br i1 [[CMP]], label %[[EXIT:.*]], label %[[RECURSE:.*]]
+; CHECK:       [[RECURSE]]:
+; CHECK-NEXT:    [[SUB:%.*]] = sub i32 [[N]], 1
+; CHECK-NEXT:    [[MUL:%.*]] = mul i32 [[ACCUM]], [[SUB]]
+; CHECK-NEXT:    [[CALL:%.*]] = call i32 @foo2(i32 [[MUL]], i32 [[SUB]])
+; CHECK-NEXT:    call void @foo3()
+; CHECK-NEXT:    br label %[[EXIT]]
+; CHECK:       [[EXIT]]:
+; CHECK-NEXT:    [[RES:%.*]] = phi i32 [ [[ACCUM]], %[[ENTRY]] ], [ [[CALL]], %[[RECURSE]] ]
+; CHECK-NEXT:    ret i32 [[RES]]
+;
+entry:
+  %cmp = icmp eq i32 %n, 0
+  br i1 %cmp, label %exit, label %recurse
+
+recurse:
+  %sub = sub i32 %n, 1
+  %mul = mul i32 %accum, %sub
+  %call = call i32 @foo2(i32 %mul, i32 %sub)
+  call void @foo3()
+  br label %exit
+
+exit:
+  %res = phi i32 [ %accum, %entry ], [ %call, %recurse ]
+  ret i32 %res
+}
+
+define internal i32 @foo1() {
+; CHECK-LABEL: define internal i32 @foo1() {
+; CHECK-NEXT:    [[RES:%.*]] = call i32 @foo2(i32 1, i32 5)
+; CHECK-NEXT:    ret i32 [[RES]]
+;
+  %res = call i32 @foo2(i32 1, i32 5)
+  ret i32 %res
+}
+
+define dso_local i32 @main() {
+; CHECK-LABEL: define dso_local i32 @main() {
+; CHECK-NEXT:    [[RES:%.*]] = call i32 @foo1()
+; CHECK-NEXT:    ret i32 [[RES]]
+;
+  %res = call i32 @foo1()
+  ret i32 %res
+}
+;.
+; CHECK: attributes #[[ATTR0]] = { norecurse }
+;.

llvm/test/Transforms/FunctionAttrs/norecurse_multinode_refscc.ll

@@ -0,0 +1,41 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --check-attributes --check-globals all --version 5
+; RUN: opt -passes=norecurse-lto-inference -S %s | FileCheck %s
+
+; This is a negative test which results in RefSCC with size > 1.
+; RefSCC : [(f2), (f1)]
+; --- SCC A (f1) --- size() = 1
+define internal void @f1() {
+; CHECK-LABEL: define internal void @f1() {
+; CHECK-NEXT:    call void @f2()
+; CHECK-NEXT:    ret void
+;
+  call void @f2()
+  ret void
+}
+
+; --- SCC B (f2) --- size() = 1
+; f2 indirectly calls f1 using locally allocated function pointer
+define internal void @f2() {
+; CHECK-LABEL: define internal void @f2() {
+; CHECK-NEXT:    [[FP:%.*]] = alloca ptr, align 8
+; CHECK-NEXT:    store ptr @f1, ptr [[FP]], align 8
+; CHECK-NEXT:    [[TMP:%.*]] = load ptr, ptr [[FP]], align 8
+; CHECK-NEXT:    call void [[TMP]]()
+; CHECK-NEXT:    ret void
+;
+  %fp = alloca void ()*
+  store void ()* @f1, void ()** %fp
+  %tmp = load void ()*, void ()** %fp
+  call void %tmp()
+  ret void
+}
+
+define i32 @main() {
+; CHECK-LABEL: define i32 @main() {
+; CHECK-NEXT:    call void @f1()
+; CHECK-NEXT:    ret i32 0
+;
+  call void @f1()
+  ret i32 0
+}
+