libLTO, llvm-lto, gold: Introduce flag for controlling optimization level.

This change also introduces a link-time optimization level of 1. This
optimization level runs only the globaldce pass as well as cleanup passes for
passes that run at -O0, specifically simplifycfg which cleans up lowerbitsets.

http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20150316/266951.html

llvm-svn: 232769

1 files changed, 12 insertions, 4 deletions

diff --git a/llvm/lib/Transforms/IPO/PassManagerBuilder.cpp b/llvm/lib/Transforms/IPO/PassManagerBuilder.cpp
index 8c1e039484b..46e221037ca 100644
--- a/llvm/lib/Transforms/IPO/PassManagerBuilder.cpp
+++ b/llvm/lib/Transforms/IPO/PassManagerBuilder.cpp
@@ -491,10 +491,10 @@ void PassManagerBuilder::addLTOOptimizationPasses(legacy::PassManagerBase &PM) {
   addExtensionsToPM(EP_Peephole, PM);
 
   PM.add(createJumpThreadingPass());
+}
 
-  // Lower bitset metadata to bitsets.
-  PM.add(createLowerBitSetsPass());
-
+void PassManagerBuilder::addLateLTOOptimizationPasses(
+    legacy::PassManagerBase &PM) {
   // Delete basic blocks, which optimization passes may have killed.
   PM.add(createCFGSimplificationPass());
 
@@ -516,9 +516,17 @@ void PassManagerBuilder::populateLTOPassManager(legacy::PassManagerBase &PM) {
     PM.add(createDebugInfoVerifierPass());
   }
 
-  if (OptLevel != 0)
+  if (OptLevel > 1)
     addLTOOptimizationPasses(PM);
 
+  // Lower bit sets to globals. This pass supports Clang's control flow
+  // integrity mechanisms (-fsanitize=cfi*) and needs to run at link time if CFI
+  // is enabled. The pass does nothing if CFI is disabled.
+  PM.add(createLowerBitSetsPass());
+
+  if (OptLevel != 0)
+    addLateLTOOptimizationPasses(PM);
+
   if (VerifyOutput) {
     PM.add(createVerifierPass());
     PM.add(createDebugInfoVerifierPass());