[WinEH] Ignore lifetime.end PHI nodes in empty cleanuppads

[andrew.w.kaylor]

Summary

This fixes a bug where a PHI node that is only referenced by a lifetime.end intrinsic in an otherwise empty cleanuppad can cause SimplyCFG to create an SSA violation while removing the empty cleanuppad. Theoretically the same problem can occur with debug intrinsics.

We were already deleting cleanup pads that contain lifetime.end intrinsics, and thus deleting the lifetime.end in the process. This patch just allows us to continue doing that correctly when the lifetime.end takes a local PHI as its pointer operand.

[rnk]

lgtm

llvm/lib/Transforms/Utils/SimplifyCFG.cpp

if (UnwindDest) {
     // Sink any remaining PHI nodes directly into UnwindDest.
     Instruction *InsertPt = DestEHPad;
     for (BasicBlock::iterator I = BB->begin(),
                               IE = BB->getFirstNonPHI()->getIterator();
          I != IE;) {
       // The iterator must be incremented here because the instructions are
       // being moved to another block.
       PHINode *PN = cast<PHINode>(I++);
-      if (PN->use_empty())
-        // If the PHI node has no uses, just leave it.  It will be erased
-        // when we erase BB below.
+      if (PN->use_empty() || !PN->isUsedOutsideOfBlock(BB))
+        // If the PHI node has no uses or all of its uses are in this basic
+        // block (meaning they are debug or lifetime intrinsics), just leave
+        // it.  It will be erased when we erase BB below.
         continue;
 
       // Otherwise, sink this PHI node into UnwindDest.
       // Any predecessors to UnwindDest which are not already represented
       // must be back edges which inherit the value from the path through
       // BB.  In this case, the PHI value must reference itself.
       for (auto *pred : predecessors(UnwindDest))
         if (pred != BB)

llvm/test/Transforms/SimplifyCFG/empty-cleanuppad.ll

 
 cleanupret1:
   cleanupret from %cp unwind to caller
 
 cleanupret2:
   cleanupret from %cp unwind to caller
 }
 
+; CHECK-LABEL: define void @f11(
+;   This case tests the handling of an empty cleanup pad that
+;   contains a lifetime_end intrinsic and does not dominate its
+;   successor.
+; CHECK: entry:
+; CHECK:   invoke void @g()
+; CHECK: invoke.cont:
+; CHECK:   invoke void @g()
+; CHECK: invoke.cont2:
+; CHECK:   invoke void @g()
+; CHECK-NOT: ehcleanup:
+; CHECK-NOT:   phi
+; CHECK-NOT:   cleanuppad
+; CHECK-NOT:   lifetime.end
+; CHECK: catch.dispatch:
+; CHECK:   catchswitch
+; CHECK: catch:
+; CHECK:   catchret
+; CHECK: }
+define void @f11() personality i8* bitcast (i32 (...)* @__CxxFrameHandler3 to i8*) {
+entry:
+  invoke void @g()
+          to label %invoke.cont unwind label %ehcleanup
+
+invoke.cont:                                      ; preds = %entry
+  invoke void @g()
+          to label %invoke.cont2 unwind label %ehcleanup
+
+invoke.cont2:                                     ; preds = %invoke.cont
+  invoke void @g()
+          to label %return unwind label %catch.dispatch
+
+ehcleanup:                                        ; preds = %invoke.cont, %entry
+  %x = phi i8* [ undef, %invoke.cont ], [ undef, %entry ]
+  %0 = cleanuppad within none []
+  call void @llvm.lifetime.end.p0i8(i64 16, i8* nonnull %x)
+  cleanupret from %0 unwind label %catch.dispatch
+
+catch.dispatch:                                   ; preds = %ehcleanup, %invoke.cont
+  %cs1 = catchswitch within none [label %catch] unwind to caller
+
+catch:                                            ; preds = %catch.dispatch
+  %1 = catchpad within %cs1 [i8* null, i32 u0x40, i8* null]
+  catchret from %1 to label %return
+
+return:                                           ; preds = %invoke.cont, %catch.cont
+  ret void
+}
+
 %struct.S = type { i8 }
 %struct.S2 = type { i8 }
 declare void @"\01??1S2@@QEAA@XZ"(%struct.S2*)
 declare void @g()
 declare void @use_x(i32 %x)
 
 declare i32 @__CxxFrameHandler3(...)
 
 declare void @llvm.lifetime.start.p0i8(i64, i8* nocapture)
 declare void @llvm.lifetime.end.p0i8(i64, i8* nocapture)