remove a bogus assertion: the latch block of a loop is not

neccesarily an uncond branch to the header.  This fixes 
PR8955 (the assertion tripping).

llvm-svn: 123219

2 files changed, 36 insertions, 6 deletions

diff --git a/llvm/lib/Transforms/Scalar/LoopRotation.cpp b/llvm/lib/Transforms/Scalar/LoopRotation.cpp
index d1c975f2e99..3bc4b1d2f1c 100644
--- a/llvm/lib/Transforms/Scalar/LoopRotation.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopRotation.cpp
@@ -335,12 +335,11 @@ bool LoopRotate::rotateLoop(Loop *L) {
   assert(L->getLoopPreheader() && "Invalid loop preheader after loop rotation");
   assert(L->getLoopLatch() && "Invalid loop latch after loop rotation");
 
-  // Now that the CFG and DomTree are in a consistent state again, merge the
-  // OrigHeader block into OrigLatch.  We know that they are joined by an
-  // unconditional branch.  This is just a cleanup so the emitted code isn't
-  // too gross.
-  bool DidIt = MergeBlockIntoPredecessor(OrigHeader, this);
-  assert(DidIt && "Block merge failed??"); (void)DidIt;
+  // Now that the CFG and DomTree are in a consistent state again, try to merge
+  // the OrigHeader block into OrigLatch.  This will succeed if they are
+  // connected by an unconditional branch.  This is just a cleanup so the
+  // emitted code isn't too gross in this common case.
+  MergeBlockIntoPredecessor(OrigHeader, this);
   
   ++NumRotated;
   return true;
diff --git a/llvm/test/Transforms/LoopRotate/crash.ll b/llvm/test/Transforms/LoopRotate/crash.ll
new file mode 100644
index 00000000000..d9dc803cd11
--- /dev/null
+++ b/llvm/test/Transforms/LoopRotate/crash.ll
@@ -0,0 +1,31 @@
+; RUN: opt -loop-rotate %s -disable-output
+
+target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64"
+target triple = "x86_64-apple-darwin10.0.0"
+
+; PR8955 - Rotating an outer loop that has a condbr for a latch block.
+define void @test1() nounwind ssp {
+entry:
+  br label %lbl_283
+
+lbl_283:                                          ; preds = %if.end, %entry
+  br i1 undef, label %if.else, label %if.then
+
+if.then:                                          ; preds = %lbl_283
+  br i1 undef, label %if.end, label %for.condthread-pre-split
+
+for.condthread-pre-split:                         ; preds = %if.then
+  br label %for.cond
+
+for.cond:                                         ; preds = %for.cond, %for.condthread-pre-split
+  br i1 undef, label %lbl_281, label %for.cond
+
+lbl_281:                                          ; preds = %if.end, %for.cond
+  br label %if.end
+
+if.end:                                           ; preds = %lbl_281, %if.then
+  br i1 undef, label %lbl_283, label %lbl_281
+
+if.else:                                          ; preds = %lbl_283
+  ret void
+}