Protect user-supplied runtime library functions in LTO

Add user-supplied C runtime and compiler-rt library functions to
llvm.compiler.used to protect them from premature optimization by
passes like -globalopt and -ipsccp.  Calls to (seemingly unused)
runtime library functions can be added by -instcombine and instruction
lowering.

Patch by Duncan Exon Smith, thanks!

Fixes <rdar://problem/14740087>

llvm-svn: 194514

1 files changed, 27 insertions, 0 deletions

diff --git a/llvm/test/LTO/runtime-library.ll b/llvm/test/LTO/runtime-library.ll
new file mode 100644
index 00000000000..76fc6f0cc47
--- /dev/null
+++ b/llvm/test/LTO/runtime-library.ll
@@ -0,0 +1,27 @@
+; runtime library implementations should be added to llvm.compiler.used
+; RUN: llvm-as <%s >%t1
+; RUN: llvm-lto -o %t2 %t1
+; RUN: llvm-nm -no-sort %t2 | FileCheck %s -check-prefix=KEEP -check-prefix=LOSE
+
+target triple = "x86_64-apple-darwin9"
+
+; KEEP-LABEL: _puts
+define void @puts() {
+  ret void
+}
+
+; KEEP-LABEL: ___divti3
+define void @__divti3() {
+  ret void
+}
+
+; KEEP-LABEL: _memset
+define void @memset() {
+  ret void
+}
+
+; LOSE-NOT: _myprintf
+define void @myprintf() {
+  ret void
+}
+