[llvm-commits] [llvm] r150174 - in /llvm/trunk: lib/Transforms/IPO/GlobalOpt.cpp test/Transforms/GlobalOpt/cxx-dtor.ll

[Benjamin Kramer]

Author: d0k
Date: Thu Feb  9 08:26:06 2012
New Revision: 150174

URL: http://llvm.org/viewvc/llvm-project?rev=150174&view=rev
Log:
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.

Modified:
    llvm/trunk/lib/Transforms/IPO/GlobalOpt.cpp
    llvm/trunk/test/Transforms/GlobalOpt/cxx-dtor.ll

Modified: llvm/trunk/lib/Transforms/IPO/GlobalOpt.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/IPO/GlobalOpt.cpp?rev=150174&r1=150173&r2=150174&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/IPO/GlobalOpt.cpp (original)
+++ llvm/trunk/lib/Transforms/IPO/GlobalOpt.cpp Thu Feb  9 08:26:06 2012
@@ -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;

Modified: llvm/trunk/test/Transforms/GlobalOpt/cxx-dtor.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/GlobalOpt/cxx-dtor.ll?rev=150174&r1=150173&r2=150174&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/GlobalOpt/cxx-dtor.ll (original)
+++ llvm/trunk/test/Transforms/GlobalOpt/cxx-dtor.ll Thu Feb  9 08:26:06 2012
@@ -2,6 +2,7 @@
 
 %0 = type { i32, void ()* }
 %struct.A = type { i8 }
+%struct.B = type { }
 
 @a = global %struct.A zeroinitializer, align 1
 @__dso_handle = external global i8*
@@ -15,13 +16,14 @@
 }
 
 define linkonce_odr void @_ZN1AD1Ev(%struct.A* %this) nounwind align 2 {
-  call void @_ZN1AD2Ev(%struct.A* %this)
+  %t = bitcast %struct.A* %this to %struct.B*
+  call void @_ZN1BD1Ev(%struct.B* %t)
   ret void
 }
 
 declare i32 @__cxa_atexit(void (i8*)*, i8*, i8*)
 
-define linkonce_odr void @_ZN1AD2Ev(%struct.A* %this) nounwind align 2 {
+define linkonce_odr void @_ZN1BD1Ev(%struct.B* %this) nounwind align 2 {
   ret void
 }