[ARM] Handle all-ones mask explicitly in targetShrinkDemandedConstant.

This avoids a potential infinite loop setting and unsetting bits in the
mask.

Reduced from a failure on the polly-aosp bot.

Differential Revision: https://reviews.llvm.org/D51066

llvm-svn: 340446

1 files changed, 35 insertions, 0 deletions

diff --git a/llvm/test/CodeGen/ARM/demanded-bits-and.ll b/llvm/test/CodeGen/ARM/demanded-bits-and.ll
new file mode 100644
index 00000000000..42b6ca5e644
--- /dev/null
+++ b/llvm/test/CodeGen/ARM/demanded-bits-and.ll
@@ -0,0 +1,35 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -mtriple=arm-eabi < %s | FileCheck %s
+
+; Make sure this doesn't hang, and there are no unnecessary
+; "and" instructions.
+
+define dso_local void @f(i16* %p) {
+; CHECK-LABEL: f:
+; CHECK:       @ %bb.0: @ %entry
+; CHECK-NEXT:  .LBB0_1: @ %bb
+; CHECK-NEXT:    @ =>This Inner Loop Header: Depth=1
+; CHECK-NEXT:    ldrh r1, [r0]
+; CHECK-NEXT:    and r2, r1, #255
+; CHECK-NEXT:    add r3, r2, r1, lsr #8
+; CHECK-NEXT:    add r2, r3, r2
+; CHECK-NEXT:    add r1, r2, r1, lsr #8
+; CHECK-NEXT:    add r1, r1, #2
+; CHECK-NEXT:    lsr r1, r1, #2
+; CHECK-NEXT:    strh r1, [r0]
+; CHECK-NEXT:    b .LBB0_1
+entry:
+  br label %bb
+
+bb:
+  %_p_scalar_ = load i16, i16* %p, align 2
+  %p_and = and i16 %_p_scalar_, 255
+  %p_ = lshr i16 %_p_scalar_, 8
+  %p_add = add nuw nsw i16 %p_, 2
+  %p_add14 = add nuw nsw i16 %p_add, %p_and
+  %p_add18 = add nuw nsw i16 %p_add14, %p_and
+  %p_add19 = add nuw nsw i16 %p_add18, %p_
+  %p_200 = lshr i16 %p_add19, 2
+  store i16 %p_200, i16* %p, align 2
+  br label %bb
+}