LoopIdiom: Give up when the loop is not in canonical form.

We rely on it when doing the transforms. This can happen when there is an
indirectbr in  the loop.

Fixes PR13892.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@164383 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 39 insertions, 0 deletions

diff --git a/lib/Transforms/Scalar/LoopIdiomRecognize.cpp b/lib/Transforms/Scalar/LoopIdiomRecognize.cpp
index a72e288303..1553328c07 100644
--- a/lib/Transforms/Scalar/LoopIdiomRecognize.cpp
+++ b/lib/Transforms/Scalar/LoopIdiomRecognize.cpp
@@ -175,6 +175,11 @@ static void deleteIfDeadInstruction(Value *V, ScalarEvolution &SE,
 bool LoopIdiomRecognize::runOnLoop(Loop *L, LPPassManager &LPM) {
   CurLoop = L;
 
+  // If the loop could not be converted to canonical form, it must have an
+  // indirectbr in it, just give up.
+  if (!L->getLoopPreheader())
+    return false;
+
   // Disable loop idiom recognition if the function's name is a common idiom.
   StringRef Name = L->getHeader()->getParent()->getName();
   if (Name == "memset" || Name == "memcpy")
diff --git a/test/Transforms/LoopIdiom/non-canonical-loop.ll b/test/Transforms/LoopIdiom/non-canonical-loop.ll
new file mode 100644
index 0000000000..a6a4f9227f
--- /dev/null
+++ b/test/Transforms/LoopIdiom/non-canonical-loop.ll
@@ -0,0 +1,34 @@
+; RUN: opt -S -loop-idiom < %s
+; Don't crash
+; PR13892
+
+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-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define void @test(i32* %currMB) nounwind uwtable {
+entry:
+  br i1 undef, label %start.exit, label %if.then.i
+
+if.then.i:                                        ; preds = %entry
+  unreachable
+
+start.exit:                       ; preds = %entry
+  indirectbr i8* undef, [label %0, label %for.bodyprime]
+
+; <label>:0                                       ; preds = %start.exit
+  unreachable
+
+for.bodyprime:                                    ; preds = %for.bodyprime, %start.exit
+  %i.057375 = phi i32 [ 0, %start.exit ], [ %1, %for.bodyprime ]
+  %arrayidx8prime = getelementptr inbounds i32* %currMB, i32 %i.057375
+  store i32 0, i32* %arrayidx8prime, align 4
+  %1 = add i32 %i.057375, 1
+  %cmp5prime = icmp slt i32 %1, 4
+  br i1 %cmp5prime, label %for.bodyprime, label %for.endprime
+
+for.endprime:                                     ; preds = %for.bodyprime
+  br label %for.body23prime
+
+for.body23prime:                                  ; preds = %for.body23prime, %for.endprime
+  br label %for.body23prime
+}