From 1693b80bd567cd398365c5f23af0b7ce86cd1f6b Mon Sep 17 00:00:00 2001 From: Roman Lebedev Date: Mon, 22 Jul 2019 22:09:02 +0000 Subject: [PATCH] [SimplifyCFG][NFC] Test that we fail to flatten CFG in JPEG "sign" value extend pattern MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit This comes up in JPEG decoding, see e.g. Figure F.12 – Extending the sign bit of a decoded value in V of ITU T.81 (JPEG specification). llvm-svn: 366750 --- .../SimplifyCFG/signbit-like-value-extension.ll | 39 ++++++++++++++++++++++ 1 file changed, 39 insertions(+) create mode 100644 llvm/test/Transforms/SimplifyCFG/signbit-like-value-extension.ll diff --git a/llvm/test/Transforms/SimplifyCFG/signbit-like-value-extension.ll b/llvm/test/Transforms/SimplifyCFG/signbit-like-value-extension.ll new file mode 100644 index 0000000..ea013ef --- /dev/null +++ b/llvm/test/Transforms/SimplifyCFG/signbit-like-value-extension.ll @@ -0,0 +1,39 @@ +; NOTE: Assertions have been autogenerated by utils/update_test_checks.py +; RUN: opt < %s -simplifycfg -S | FileCheck %s + +; This looks like a normal sign extension, but it's not. +; This comes up in JPEG decoding. This check is really unpredictable, +; so it is likely beneficial to avoid the branch. + +define i32 @extend_value(i32 %storage, i32 %nbits) { +; CHECK-LABEL: @extend_value( +; CHECK-NEXT: bb: +; CHECK-NEXT: [[SKIPNBITS:%.*]] = sub i32 32, [[NBITS:%.*]] +; CHECK-NEXT: [[VALUE:%.*]] = lshr i32 [[STORAGE:%.*]], [[SKIPNBITS]] +; CHECK-NEXT: [[SHOULDEXTEND:%.*]] = icmp sgt i32 [[STORAGE]], -1 +; CHECK-NEXT: br i1 [[SHOULDEXTEND]], label [[EXTEND:%.*]], label [[END:%.*]] +; CHECK: extend: +; CHECK-NEXT: [[HIGHBITMASK:%.*]] = shl nsw i32 -1, [[NBITS]] +; CHECK-NEXT: [[HIGHBITMASKPLUSONE:%.*]] = add nsw i32 [[HIGHBITMASK]], 1 +; CHECK-NEXT: [[EXTENDED:%.*]] = add i32 [[HIGHBITMASKPLUSONE]], [[VALUE]] +; CHECK-NEXT: br label [[END]] +; CHECK: end: +; CHECK-NEXT: [[RES:%.*]] = phi i32 [ [[EXTENDED]], [[EXTEND]] ], [ [[VALUE]], [[BB:%.*]] ] +; CHECK-NEXT: ret i32 [[RES]] +; +bb: + %skipnbits = sub i32 32, %nbits + %value = lshr i32 %storage, %skipnbits + %shouldextend = icmp sgt i32 %storage, -1 + br i1 %shouldextend, label %extend, label %end + +extend: ; preds = %bb + %highbitmask = shl nsw i32 -1, %nbits + %highbitmaskplusone = add nsw i32 %highbitmask, 1 + %extended = add i32 %highbitmaskplusone, %value + br label %end + +end: ; preds = %extend, %bb + %res = phi i32 [ %extended, %extend ], [ %value, %bb ] + ret i32 %res +} -- 2.7.4