[Polly CodeGen] Break critical edge from RTC to original loop.

This makes polly generate a CFG which is closer to what we want
in LLVM IR, with a loop preheader for the original loop. This is
just a cleanup, but it exposes some fragile assumptions.

I'm not completely happy with the changes related to expandCodeFor;
RTCBB->getTerminator() is basically a random insertion point which
happens to work due to the way we generate runtime checks. I'm not
sure what the right answer looks like, though.

Differential Revision: https://reviews.llvm.org/D26053

llvm-svn: 285864

1 files changed, 2 insertions, 1 deletions

diff --git a/polly/lib/CodeGen/IslNodeBuilder.cpp b/polly/lib/CodeGen/IslNodeBuilder.cpp
index 0869a7fc86b..5c50fbf0e88 100644
--- a/polly/lib/CodeGen/IslNodeBuilder.cpp
+++ b/polly/lib/CodeGen/IslNodeBuilder.cpp
@@ -1286,7 +1286,8 @@ Value *IslNodeBuilder::generateSCEV(const SCEV *Expr) {
          "Insert location points after last valid instruction");
   Instruction *InsertLocation = &*Builder.GetInsertPoint();
   return expandCodeFor(S, SE, DL, "polly", Expr, Expr->getType(),
-                       InsertLocation, &ValueMap);
+                       InsertLocation, &ValueMap,
+                       StartBlock->getSinglePredecessor());
 }
 
 /// The AST expression we generate to perform the run-time check assumes