GlobalOpt: Be more aggressive about elminating side-effect free static dtors.
GlobalOpt runs early in the pipeline (before inlining) and complex class
hierarchies often introduce bitcasts or GEPs which weren't optimized away.
Teach it to ignore side-effect free instructions instead of depending on
other passes to remove them.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@150174 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/IPO/GlobalOpt.cpp b/lib/Transforms/IPO/GlobalOpt.cpp
index 6fa57b4..788fee0 100644
--- a/lib/Transforms/IPO/GlobalOpt.cpp
+++ b/lib/Transforms/IPO/GlobalOpt.cpp
@@ -2753,7 +2753,8 @@
/// destructor and can therefore be eliminated.
/// Note that we assume that other optimization passes have already simplified
/// the code so we only look for a function with a single basic block, where
-/// the only allowed instructions are 'ret' or 'call' to empty C++ dtor.
+/// the only allowed instructions side-effect free, 'ret' or 'call' to empty
+/// C++ dtor.
static bool cxxDtorIsEmpty(const Function &Fn,
SmallPtrSet<const Function *, 8> &CalledFunctions) {
// FIXME: We could eliminate C++ destructors if they're readonly/readnone and
@@ -2786,9 +2787,9 @@
if (!cxxDtorIsEmpty(*CalledFn, NewCalledFunctions))
return false;
} else if (isa<ReturnInst>(*I))
- return true;
- else
- return false;
+ return true; // We're done.
+ else if (I->mayHaveSideEffects())
+ return false; // Destructor with side effects, bail.
}
return false;