SROA: Don't insert instructions before a PHI

SROA may decide that it needs to insert a bitcast and would set it's
insertion point before a PHI.  This will create an invalid module
right quick.

Instead, choose the first insertion point in the basic block that holds
our PHI.

This fixes PR20822.

Differential Revision: http://reviews.llvm.org/D5141

llvm-svn: 216891

1 files changed, 4 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/Scalar/SROA.cpp b/llvm/lib/Transforms/Scalar/SROA.cpp
index da5f14a7888..32a61a0b9f2 100644
--- a/llvm/lib/Transforms/Scalar/SROA.cpp
+++ b/llvm/lib/Transforms/Scalar/SROA.cpp
@@ -2708,7 +2708,10 @@ private:
     // the old pointer, which necessarily must be in the right position to
     // dominate the PHI.
     IRBuilderTy PtrBuilder(IRB);
-    PtrBuilder.SetInsertPoint(OldPtr);
+    if (isa<PHINode>(OldPtr))
+      PtrBuilder.SetInsertPoint(OldPtr->getParent()->getFirstInsertionPt());
+    else
+      PtrBuilder.SetInsertPoint(OldPtr);
     PtrBuilder.SetCurrentDebugLocation(OldPtr->getDebugLoc());
 
     Value *NewPtr = getNewAllocaSlicePtr(PtrBuilder, OldPtr->getType());