[MBP] do not reorder and move up loop latch block

Do not reorder and move up a loop latch block before a loop header
when optimising for size because this will generate an extra 
unconditional branch.

Differential Revision: https://reviews.llvm.org/D22521

llvm-svn: 278840

1 files changed, 35 insertions, 0 deletions

diff --git a/llvm/test/CodeGen/X86/loop-blocks.ll b/llvm/test/CodeGen/X86/loop-blocks.ll
index 1a1d11e6cb3..fc6a357523f 100644
--- a/llvm/test/CodeGen/X86/loop-blocks.ll
+++ b/llvm/test/CodeGen/X86/loop-blocks.ll
@@ -228,6 +228,41 @@ done:
   ret void
 }
 
+; This is exactly the same function as slightly_more_involved.
+; The difference is that when optimising for size, we do not want
+; to see this reordering.
+
+; CHECK-LABEL: slightly_more_involved_2:
+; CHECK-NOT:      jmp .LBB5_1
+; CHECK:          .LBB5_1:
+; CHECK-NEXT:     callq body
+
+define void @slightly_more_involved_2() #0 {
+entry:
+  br label %loop
+
+loop:
+  call void @body()
+  %t0 = call i32 @get()
+  %t1 = icmp slt i32 %t0, 2
+  br i1 %t1, label %block_a, label %bb
+
+bb:
+  %t2 = call i32 @get()
+  %t3 = icmp slt i32 %t2, 99
+  br i1 %t3, label %exit, label %loop
+
+block_a:
+  call void @bar99()
+  br label %loop
+
+exit:
+  call void @exit()
+  ret void
+}
+
+attributes #0 = { minsize norecurse nounwind optsize readnone uwtable }
+
 declare void @bar99() nounwind
 declare void @bar100() nounwind
 declare void @bar101() nounwind