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

Originally reviewed here: http://reviews.llvm.org/D17463

llvm-svn: 272023

1 files changed, 5 insertions, 2 deletions

diff --git a/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp b/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
index 8d9124670b0..8d103843b5e 100644
--- a/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
+++ b/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
@@ -7313,14 +7313,17 @@ EVT AArch64TargetLowering::getOptimalMemOpType(uint64_t Size, unsigned DstAlign,
 
 // 12-bit optionally shifted immediates are legal for adds.
 bool AArch64TargetLowering::isLegalAddImmediate(int64_t Immed) const {
+  // Avoid UB for INT64_MIN.
+  if (Immed == std::numeric_limits<int64_t>::min())
+    return false;
+  // Same encoding for add/sub, just flip the sign.
+  Immed = std::abs(Immed);
   return ((Immed >> 12) == 0 || ((Immed & 0xfff) == 0 && Immed >> 24 == 0));
 }
 
 // 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);
 }