[DeadArgElim] Split the invoke successor edge

Invoking a function which returns an aggregate can sometimes be
transformed to return a scalar value.  However, this means that we need
to create an insertvalue instruction(s) to recreate the correct
aggregate type.  We achieved this by inserting an insertvalue
instruction at the invoke's normal successor.  However, this is not
feasible if the normal successor uses the invoke's return value inside a
PHI node.

Instead, split the edge between the invoke and the unwind successor and
create the insertvalue instruction in the new basic block.  The new
basic block's successor will be the old invoke successor which leaves
us with IR which is well behaved.

This fixes PR24906.

llvm-svn: 248387

llvm/lib/Transforms/IPO/DeadArgumentElimination.cpp

@@ -35,6 +35,7 @@
 #include "llvm/Pass.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/raw_ostream.h"
+#include "llvm/Transforms/Utils/BasicBlockUtils.h"
 #include <map>
 #include <set>
 #include <tuple>
@@ -967,7 +968,7 @@ bool DAE::RemoveDeadStuffFromFunction(Function *F) {
     Instruction *New;
     if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
       New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(),
-                               Args, "", Call);
+                               Args, "", Call->getParent());
       cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv());
       cast<InvokeInst>(New)->setAttributes(NewCallPAL);
     } else {
@@ -997,9 +998,8 @@ bool DAE::RemoveDeadStuffFromFunction(Function *F) {
                " must have been a struct or an array!");
         Instruction *InsertPt = Call;
         if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
-          BasicBlock::iterator IP = II->getNormalDest()->begin();
-          while (isa<PHINode>(IP)) ++IP;
-          InsertPt = IP;
+          BasicBlock *NewEdge = SplitEdge(New->getParent(), II->getNormalDest());
+          InsertPt = NewEdge->getFirstInsertionPt();
         }
 
         // We used to return a struct or array. Instead of doing smart stuff

llvm/test/Transforms/DeadArgElim/aggregates.ll

@@ -159,4 +159,28 @@ define internal i8 @outer() {
 
   %val = load i8, i8* %resptr
   ret i8 %val
-}
+}
+
+define internal { i32 } @agg_ret() {
+entry:
+  unreachable
+}
+
+; CHECK-LABEL: define void @PR24906
+; CHECK: %[[invoke:.*]] = invoke i32 @agg_ret()
+; CHECK: %[[oldret:.*]] = insertvalue { i32 } undef, i32 %[[invoke]], 0
+; CHECK: phi { i32 } [ %[[oldret]],
+define void @PR24906() personality i32 (i32)* undef {
+entry:
+  %tmp2 = invoke { i32 } @agg_ret()
+          to label %bb3 unwind label %bb4
+
+bb3:
+  %tmp3 = phi { i32 } [ %tmp2, %entry ]
+  unreachable
+
+bb4:
+  %tmp4 = landingpad { i8*, i32 }
+          cleanup
+  unreachable
+}