Rework a bit of the implementation of loop block rotation to not rely so

heavily on AnalyzeBranch. That routine doesn't behave as we want given
that rotation occurs mid-way through re-ordering the function. Instead
merely check that there are not unanalyzable branching constructs
present, and then reason about the CFG via successor lists. This
actually simplifies my mental model for all of this as well.

The concrete result is that we now will rotate more loop chains. I've
added a test case from Olden highlighting the effect. There is still
a bit more to do here though in order to regain all of the performance
in Olden.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@145179 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 39 insertions, 1 deletions

diff --git a/test/CodeGen/X86/block-placement.ll b/test/CodeGen/X86/block-placement.ll
index 66def49e4b..52f7c3081c 100644
--- a/test/CodeGen/X86/block-placement.ll
+++ b/test/CodeGen/X86/block-placement.ll
@@ -199,6 +199,44 @@ exit:
   ret i32 %base
 }
 
+define void @test_loop_rotate_reversed_blocks() {
+; This test case (greatly reduced from an Olden bencmark) ensures that the loop
+; rotate implementation doesn't assume that loops are laid out in a particular
+; order. The first loop will get split into two basic blocks, with the loop
+; header coming after the loop latch.
+;
+; CHECK: test_loop_rotate_reversed_blocks
+; CHECK: %entry
+; Look for a jump into the middle of the loop, and no branches mid-way.
+; CHECK: jmp
+; CHECK: %loop1
+; CHECK-NOT: j{{\w*}} .LBB{{.*}}
+; CHECK: %loop1
+; CHECK: je
+
+entry:
+  %cond1 = load volatile i1* undef
+  br i1 %cond1, label %loop2.preheader, label %loop1
+
+loop1:
+  call i32 @f()
+  %cond2 = load volatile i1* undef
+  br i1 %cond2, label %loop2.preheader, label %loop1
+
+loop2.preheader:
+  call i32 @f()
+  %cond3 = load volatile i1* undef
+  br i1 %cond3, label %exit, label %loop2
+
+loop2:
+  call i32 @f()
+  %cond4 = load volatile i1* undef
+  br i1 %cond4, label %exit, label %loop2
+
+exit:
+  ret void
+}
+
 define i32 @test_loop_align(i32 %i, i32* %a) {
 ; Check that we provide basic loop body alignment with the block placement
 ; pass.
@@ -567,8 +605,8 @@ define void @test_unnatural_cfg_backwards_inner_loop() {
 ; CHECK: test_unnatural_cfg_backwards_inner_loop
 ; CHECK: %entry
 ; CHECK: %body
-; CHECK: %loop1
 ; CHECK: %loop2b
+; CHECK: %loop1
 ; CHECK: %loop2a
 
 entry: