[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, 39 insertions, 0 deletions

diff --git a/clang/test/CodeGenCXX/stack-reuse-miscompile.cpp b/clang/test/CodeGenCXX/stack-reuse-miscompile.cpp
new file mode 100644
index 00000000000..e6b9cbe3365
--- /dev/null
+++ b/clang/test/CodeGenCXX/stack-reuse-miscompile.cpp
@@ -0,0 +1,39 @@
+// RUN: %clang -S -emit-llvm -O1 -mllvm -disable-llvm-optzns -S %s -o - | FileCheck %s
+
+// This test should not to generate llvm.lifetime.start/llvm.lifetime.end for
+// f function because all temporary objects in this function are used for the
+// final result
+
+class S {
+  char *ptr;
+  unsigned int len;
+};
+
+class T {
+  S left;
+  S right;
+
+public:
+  T(const char s[]);
+  T(S);
+
+  T concat(const T &Suffix) const;
+  const char * str() const;
+};
+
+const char * f(S s)
+{
+// CHECK: %1 = alloca %class.T, align 4
+// CHECK: %2 = alloca %class.T, align 4
+// CHECK: %3 = alloca %class.S, align 4
+// CHECK: %4 = alloca %class.T, align 4
+// CHECK: %5 = call x86_thiscallcc %class.T* @"\01??0T@@QAE@QBD@Z"
+// CHECK: %6 = bitcast %class.S* %3 to i8*
+// CHECK: %7 = bitcast %class.S* %s to i8*
+// CHECK: call void @llvm.memcpy.p0i8.p0i8.i32
+// CHECK: %8 = call x86_thiscallcc %class.T* @"\01??0T@@QAE@VS@@@Z"
+// CHECK: call x86_thiscallcc void @"\01?concat@T@@QBE?AV1@ABV1@@Z"
+// CHECK: %9 = call x86_thiscallcc i8* @"\01?str@T@@QBEPBDXZ"(%class.T* %4)
+
+  return T("[").concat(T(s)).str();
+}