[AArch64] Fix isLegalAddImmediate() to return true for valid negative values.

Reviewers: t.p.northover, jmolloy

Subscribers: mcrosier, aemerson, llvm-commits, rengolin

Differential Revision: http://reviews.llvm.org/D17463

llvm-svn: 262248

1 files changed, 2 insertions, 2 deletions

diff --git a/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp b/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
index a18b7a61cc1..a6a9694a21d 100644
--- a/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
+++ b/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
@@ -7280,6 +7280,8 @@ EVT AArch64TargetLowering::getOptimalMemOpType(uint64_t Size, unsigned DstAlign,
 
 // 12-bit optionally shifted immediates are legal for adds.
 bool AArch64TargetLowering::isLegalAddImmediate(int64_t Immed) const {
+  // Same encoding for add/sub, just flip the sign.
+  Immed = std::abs(Immed);
   if ((Immed >> 12) == 0 || ((Immed & 0xfff) == 0 && Immed >> 24 == 0))
     return true;
   return false;
@@ -7288,8 +7290,6 @@ bool AArch64TargetLowering::isLegalAddImmediate(int64_t Immed) const {
 // Integer comparisons are implemented with ADDS/SUBS, so the range of valid
 // immediates is the same as for an add or a sub.
 bool AArch64TargetLowering::isLegalICmpImmediate(int64_t Immed) const {
-  if (Immed < 0)
-    Immed *= -1;
   return isLegalAddImmediate(Immed);
 }