[SimplifyCFG] Remove cleanuppads which are empty except for calls to lifetime.end

A cleanuppad is not cheap, they turn into many instructions and result
in additional spills and fills.  It is not worth keeping a cleanuppad
around if all it does is hold a lifetime.end instruction.

N.B.  We first try to merge the cleanuppad with another cleanuppad to
avoid dropping the lifetime and debug info markers.

llvm-svn: 270314

2 files changed, 48 insertions, 5 deletions

diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index fb6a13fadc5..25baf1bf640 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -3424,11 +3424,23 @@ static bool removeEmptyCleanup(CleanupReturnInst *RI) {
     // This isn't an empty cleanup.
     return false;
 
-  // Check that there are no other instructions except for debug intrinsics.
+  // Check that there are no other instructions except for benign intrinsics.
   BasicBlock::iterator I = CPInst->getIterator(), E = RI->getIterator();
-  while (++I != E)
-    if (!isa<DbgInfoIntrinsic>(I))
+  while (++I != E) {
+    auto *II = dyn_cast<IntrinsicInst>(I);
+    if (!II)
+      return false;
+
+    Intrinsic::ID IntrinsicID = II->getIntrinsicID();
+    switch (IntrinsicID) {
+    case Intrinsic::dbg_declare:
+    case Intrinsic::dbg_value:
+    case Intrinsic::lifetime_end:
+      break;
+    default:
       return false;
+    }
+  }
 
   // If the cleanup return we are simplifying unwinds to the caller, this will
   // set UnwindDest to nullptr.
@@ -3567,10 +3579,10 @@ bool SimplifyCFGOpt::SimplifyCleanupReturn(CleanupReturnInst *RI) {
   if (isa<UndefValue>(RI->getOperand(0)))
     return false;
 
-  if (removeEmptyCleanup(RI))
+  if (mergeCleanupPad(RI))
     return true;
 
-  if (mergeCleanupPad(RI))
+  if (removeEmptyCleanup(RI))
     return true;
 
   return false;
diff --git a/llvm/test/Transforms/SimplifyCFG/empty-cleanuppad.ll b/llvm/test/Transforms/SimplifyCFG/empty-cleanuppad.ll
index 57b36288995..e83cbb50e58 100644
--- a/llvm/test/Transforms/SimplifyCFG/empty-cleanuppad.ll
+++ b/llvm/test/Transforms/SimplifyCFG/empty-cleanuppad.ll
@@ -404,6 +404,35 @@ catch.cont:                                       ; preds = %catch
 return:                                           ; preds = %invoke.cont, %catch.cont
   ret void
 }
+; CHECK-LABEL: define i32 @f9()
+; CHECK: entry:
+; CHECK:   invoke void @"\01??1S2@@QEAA@XZ"(
+; CHECK-NOT:   cleanuppad
+; CHECK: catch.dispatch:
+; CHECK: }
+define i32 @f9() personality i32 (...)* @__CxxFrameHandler3 {
+entry:
+  %s = alloca i8, align 1
+  call void @llvm.lifetime.start(i64 1, i8* nonnull %s)
+  %bc = bitcast i8* %s to %struct.S2*
+  invoke void @"\01??1S2@@QEAA@XZ"(%struct.S2* %bc)
+          to label %try.cont unwind label %ehcleanup
+
+ehcleanup:
+  %cleanup.pad = cleanuppad within none []
+  call void @llvm.lifetime.end(i64 1, i8* nonnull %s)
+  cleanupret from %cleanup.pad unwind label %catch.dispatch
+
+catch.dispatch:
+  %catch.switch = catchswitch within none [label %catch] unwind to caller
+
+catch:
+  %catch.pad = catchpad within %catch.switch [i8* null, i32 0, i8* null]
+  catchret from %catch.pad to label %try.cont
+
+try.cont:
+  ret i32 0
+}
 
 %struct.S = type { i8 }
 %struct.S2 = type { i8 }
@@ -413,3 +442,5 @@ declare void @use_x(i32 %x)
 
 declare i32 @__CxxFrameHandler3(...)
 
+declare void @llvm.lifetime.start(i64, i8* nocapture)
+declare void @llvm.lifetime.end(i64, i8* nocapture)