[LoopUnrolling] Fix loop size check for peeling

Summary:
We should check if loop size allows us to peel at least one iteration
before we do so.

Patch by Max Kazantsev!

Reviewers: sanjoy, mkuper, efriedma

Reviewed By: mkuper

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D30632

llvm-svn: 297122

1 files changed, 29 insertions, 1 deletions

diff --git a/llvm/test/Transforms/LoopUnroll/peel-loop-not-forced.ll b/llvm/test/Transforms/LoopUnroll/peel-loop-not-forced.ll
index afb03a22900..3dcac87f824 100644
--- a/llvm/test/Transforms/LoopUnroll/peel-loop-not-forced.ll
+++ b/llvm/test/Transforms/LoopUnroll/peel-loop-not-forced.ll
@@ -1,4 +1,4 @@
-; RUN: opt < %s -S -loop-unroll | FileCheck %s
+; RUN: opt < %s -S -loop-unroll -unroll-threshold=4 | FileCheck %s
 
 define i32 @invariant_backedge_1(i32 %a, i32 %b) {
 ; CHECK-LABEL: @invariant_backedge_1
@@ -18,6 +18,34 @@ loop:
   %incsum = add i32 %sum, %plus
   %inc = add i32 %i, 1
   %cmp = icmp slt i32 %i, 1000
+
+  br i1 %cmp, label %loop, label %exit
+
+exit:
+  ret i32 %sum
+}
+
+; Peeling should fail due to method size.
+define i32 @invariant_backedge_2(i32 %a, i32 %b) {
+; CHECK-LABEL: @invariant_backedge_2
+; CHECK-NOT:   loop.peel:
+; CHECK:       loop:
+; CHECK:         %i = phi
+; CHECK:         %sum = phi
+; CHECK:         %plus = phi
+entry:
+  br label %loop
+
+loop:
+  %i = phi i32 [ 0, %entry ], [ %inc, %loop ]
+  %sum = phi i32 [ 0, %entry ], [ %incsum2, %loop ]
+  %plus = phi i32 [ %a, %entry ], [ %b, %loop ]
+
+  %incsum = add i32 %sum, %plus
+  %incsum2 = add i32 %incsum, %plus
+  %inc = add i32 %i, 1
+  %cmp = icmp slt i32 %i, 1000
+
   br i1 %cmp, label %loop, label %exit
 
 exit: