[ThinLTO] Disable importing and other cross-module optis at -O0

Summary:
There is no point to importing at -O0, since we won't inline. We should
also disable other cross-module optimizations.

(Plan to backport this fix to the 3.9 branch to fix PR30774)

Reviewers: pcc

Subscribers: johanengelen, mehdi_amini

Differential Revision: https://reviews.llvm.org/D25918

llvm-svn: 285648

1 files changed, 7 insertions, 0 deletions

diff --git a/llvm/tools/llvm-lto2/llvm-lto2.cpp b/llvm/tools/llvm-lto2/llvm-lto2.cpp
index 042f874596f..b48f6c1993e 100644
--- a/llvm/tools/llvm-lto2/llvm-lto2.cpp
+++ b/llvm/tools/llvm-lto2/llvm-lto2.cpp
@@ -26,6 +26,11 @@ using namespace llvm;
 using namespace lto;
 using namespace object;
 
+static cl::opt<char>
+    OptLevel("O", cl::desc("Optimization level. [-O0, -O1, -O2, or -O3] "
+                           "(default = '-O2')"),
+             cl::Prefix, cl::ZeroOrMore, cl::init('2'));
+
 static cl::list<std::string> InputFilenames(cl::Positional, cl::OneOrMore,
                                             cl::desc("<input bitcode files>"));
 
@@ -145,6 +150,8 @@ int main(int argc, char **argv) {
   Conf.OptPipeline = OptPipeline;
   Conf.AAPipeline = AAPipeline;
 
+  Conf.OptLevel = OptLevel - '0';
+
   ThinBackend Backend;
   if (ThinLTODistributedIndexes)
     Backend = createWriteIndexesThinBackend("", "", true, "");