[Unroll] Do NOT unroll a loop with small runtime upperbound

For a runtime loop if we can compute its trip count upperbound:

Don't unroll if:
1. loop is not guaranteed to run either zero or upperbound iterations; and
2. trip count upperbound is less than UnrollMaxUpperBound
Unless user or TTI asked to do so.

If unrolling, limit unroll factor to loop's trip count upperbound.

Differential Revision: https://reviews.llvm.org/D62989

Change-Id: I6083c46a9d98b2e22cd855e60523fdc5a4929c73
llvm-svn: 373017

1 files changed, 70 insertions, 0 deletions

diff --git a/llvm/test/Transforms/LoopUnroll/runtime-small-upperbound.ll b/llvm/test/Transforms/LoopUnroll/runtime-small-upperbound.ll
new file mode 100644
index 00000000000..95632a5a3be
--- /dev/null
+++ b/llvm/test/Transforms/LoopUnroll/runtime-small-upperbound.ll
@@ -0,0 +1,70 @@
+; RUN: opt -S -loop-unroll -unroll-runtime %s -o - | FileCheck %s
+; RUN: opt -S -loop-unroll -unroll-runtime -unroll-max-upperbound=6 %s -o - | FileCheck %s --check-prefix=UPPER
+
+target datalayout = "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64"
+
+@global = dso_local local_unnamed_addr global i32 0, align 4
+@global.1 = dso_local local_unnamed_addr global i8* null, align 4
+
+; Check that loop in hoge_3, with a runtime upperbound of 3, is not unrolled.
+; CHECK-LABEL: hoge_3
+; CHECK: loop:
+; CHECK: store
+; CHECK-NOT: store
+; CHECK: br i1 %{{.*}}, label %loop
+; UPPER-LABEL: hoge_3
+; UPPER: loop:
+; UPPER: store
+; UPPER-NOT: store
+; UPPER: br i1 %{{.*}}, label %loop
+define dso_local void @hoge_3(i8 %arg) {
+entry:
+  %x = load i32, i32* @global, align 4
+  %y = load i8*, i8** @global.1, align 4
+  %0 = icmp ult i32 %x, 17
+  br i1 %0, label %loop, label %exit
+
+loop:
+  %iv = phi i32 [ %x, %entry ], [ %iv.next, %loop ]
+  %ptr = phi i8* [ %y, %entry ], [ %ptr.next, %loop ]
+  %iv.next = add nuw i32 %iv, 8
+  %ptr.next = getelementptr inbounds i8, i8* %ptr, i32 1
+  store i8 %arg, i8* %ptr.next, align 1
+  %1 = icmp ult i32 %iv.next, 17
+  br i1 %1, label %loop, label %exit
+
+exit:
+  ret void
+}
+
+; Check that loop in hoge_5, with a runtime upperbound of 5, is unrolled when -unroll-max-upperbound=4
+; CHECK-LABEL: hoge_5
+; CHECK: loop:
+; CHECK: store
+; CHECK-NOT: store
+; CHECK: br i1 %{{.*}}, label %loop
+; UPPER-LABEL: hoge_5
+; UPPER: loop:
+; UPPER: store
+; UPPER: store
+; UPPER: store
+; UPPER: br i1 %{{.*}}, label %loop
+define dso_local void @hoge_5(i8 %arg) {
+entry:
+  %x = load i32, i32* @global, align 4
+  %y = load i8*, i8** @global.1, align 4
+  %0 = icmp ult i32 %x, 17
+  br i1 %0, label %loop, label %exit
+
+loop:
+  %iv = phi i32 [ %x, %entry ], [ %iv.next, %loop ]
+  %ptr = phi i8* [ %y, %entry ], [ %ptr.next, %loop ]
+  %iv.next = add nuw i32 %iv, 4
+  %ptr.next = getelementptr inbounds i8, i8* %ptr, i32 1
+  store i8 %arg, i8* %ptr.next, align 1
+  %1 = icmp ult i32 %iv.next, 17
+  br i1 %1, label %loop, label %exit
+
+exit:
+  ret void
+}