[CodeGen] Reuse stack space from unused function results (with more accurate unused result detection)

This patch fixes issues with unused result detection which were found in patch http://reviews.llvm.org/D9743.

Differential Revision: http://reviews.llvm.org/D10042

llvm-svn: 239294

1 files changed, 146 insertions, 0 deletions

diff --git a/clang/test/CodeGenCXX/stack-reuse.cpp b/clang/test/CodeGenCXX/stack-reuse.cpp
new file mode 100644
index 00000000000..ef73d1a5387
--- /dev/null
+++ b/clang/test/CodeGenCXX/stack-reuse.cpp
@@ -0,0 +1,146 @@
+// RUN: %clang -target armv7l-unknown-linux-gnueabihf -S %s -o - -emit-llvm -O1 -disable-llvm-optzns | FileCheck %s
+
+// Stack should be reused when possible, no need to allocate two separate slots
+// if they have disjoint lifetime.
+
+// Sizes of objects are related to previously existed threshold of 32.  In case
+// of S_large stack size is rounded to 40 bytes.
+
+// 32B
+struct S_small {
+  int a[8];
+};
+
+// 36B
+struct S_large {
+  int a[9];
+};
+
+// Helper class for lifetime scope absence testing
+struct Combiner {
+  S_large a, b;
+
+  Combiner(S_large);
+  Combiner f();  
+};
+
+extern S_small foo_small();
+extern S_large foo_large();
+extern void bar_small(S_small*);
+extern void bar_large(S_large*);
+
+// Prevent mangling of function names.
+extern "C" {
+
+void small_rvoed_unnamed_temporary_object() {
+// CHECK-LABEL: define void @small_rvoed_unnamed_temporary_object
+// CHECK: call void @llvm.lifetime.start
+// CHECK: call void @_Z9foo_smallv
+// CHECK: call void @llvm.lifetime.end
+// CHECK: call void @llvm.lifetime.start
+// CHECK: call void @_Z9foo_smallv
+// CHECK: call void @llvm.lifetime.end
+
+  foo_small();
+  foo_small();
+}
+
+void large_rvoed_unnamed_temporary_object() {
+// CHECK-LABEL: define void @large_rvoed_unnamed_temporary_object
+// CHECK: call void @llvm.lifetime.start
+// CHECK: call void @_Z9foo_largev
+// CHECK: call void @llvm.lifetime.end
+// CHECK: call void @llvm.lifetime.start
+// CHECK: call void @_Z9foo_largev
+// CHECK: call void @llvm.lifetime.end
+
+  foo_large();
+  foo_large();
+}
+
+void small_rvoed_named_temporary_object() {
+// CHECK-LABEL: define void @small_rvoed_named_temporary_object
+// CHECK: call void @llvm.lifetime.start
+// CHECK: call void @_Z9foo_smallv
+// CHECK: call void @llvm.lifetime.end
+// CHECK: call void @llvm.lifetime.start
+// CHECK: call void @_Z9foo_smallv
+// CHECK: call void @llvm.lifetime.end
+
+  {
+    S_small s = foo_small();
+  }
+  {
+    S_small s = foo_small();
+  }
+}
+
+void large_rvoed_named_temporary_object() {
+// CHECK-LABEL: define void @large_rvoed_named_temporary_object
+// CHECK: call void @llvm.lifetime.start
+// CHECK: call void @_Z9foo_largev
+// CHECK: call void @llvm.lifetime.end
+// CHECK: call void @llvm.lifetime.start
+// CHECK: call void @_Z9foo_largev
+// CHECK: call void @llvm.lifetime.end
+
+  {
+    S_large s = foo_large();
+  }
+  {
+    S_large s = foo_large();
+  }
+}
+
+void small_auto_object() {
+// CHECK-LABEL: define void @small_auto_object
+// CHECK: call void @llvm.lifetime.start
+// CHECK: call void @_Z9bar_smallP7S_small
+// CHECK: call void @llvm.lifetime.end
+// CHECK: call void @llvm.lifetime.start
+// CHECK: call void @_Z9bar_smallP7S_small
+// CHECK: call void @llvm.lifetime.end
+
+  {
+    S_small s;
+    bar_small(&s);
+  }
+  {
+    S_small s;
+    bar_small(&s);
+  }
+}
+
+void large_auto_object() {
+// CHECK-LABEL: define void @large_auto_object
+// CHECK: call void @llvm.lifetime.start
+// CHECK: call void @_Z9bar_largeP7S_large
+// CHECK: call void @llvm.lifetime.end
+// CHECK: call void @llvm.lifetime.start
+// CHECK: call void @_Z9bar_largeP7S_large
+// CHECK: call void @llvm.lifetime.end
+
+  {
+    S_large s;
+    bar_large(&s);
+  }
+  {
+    S_large s;
+    bar_large(&s);
+  }
+}
+
+int large_combiner_test(S_large s) {
+// CHECK-LABEL: define i32 @large_combiner_test
+// CHECK: %1 = alloca %struct.Combiner
+// CHECK: %2 = alloca %struct.Combiner
+// CHECK: %3 = call %struct.Combiner* @_ZN8CombinerC1E7S_large(%struct.Combiner* %1, [9 x i32] %s.coerce)
+// CHECK: call void @_ZN8Combiner1fEv(%struct.Combiner* sret %2, %struct.Combiner* %1)
+// CHECK: %4 = getelementptr inbounds %struct.Combiner, %struct.Combiner* %2, i32 0, i32 0, i32 0, i32 0
+// CHECK: %5 = load i32, i32* %4
+// CHECK: ret i32 %5
+
+  return Combiner(s).f().a.a[0];
+}
+
+}