Relax an invariant that block placement was trying to assert a bit

further. This invariant just wasn't going to work in the face of
unanalyzable branches; we need to be resillient to the phenomenon of
chains poking into a loop and poking out of a loop. In fact, we already
were, we just needed to not assert on it.

This was found during a bootstrap with block placement turned on.

llvm-svn: 145100

1 files changed, 25 insertions, 0 deletions

diff --git a/llvm/test/CodeGen/X86/block-placement.ll b/llvm/test/CodeGen/X86/block-placement.ll
index c03b03ed02d..782e1542513 100644
--- a/llvm/test/CodeGen/X86/block-placement.ll
+++ b/llvm/test/CodeGen/X86/block-placement.ll
@@ -568,3 +568,28 @@ loop3:
   %next.phi = phi i32* [ %next.load, %loop2b ], [ %next.var, %loop2a ]
   br label %loop1
 }
+
+define void @unanalyzable_branch_to_loop_header() {
+; Ensure that we can handle unanalyzable branches into loop headers. We
+; pre-form chains for unanalyzable branches, and will find the tail end of that
+; at the start of the loop. This function uses floating point comparison
+; fallthrough because that happens to always produce unanalyzable branches on
+; x86.
+;
+; CHECK: unanalyzable_branch_to_loop_header
+; CHECK: %entry
+; CHECK: %loop
+; CHECK: %exit
+
+entry:
+  %cmp = fcmp une double 0.000000e+00, undef
+  br i1 %cmp, label %loop, label %exit
+
+loop:
+  %cond = icmp eq i8 undef, 42
+  br i1 %cond, label %exit, label %loop
+
+exit:
+  ret void
+}
+