Fix ARMTargetLowering::isLegalAddImmediate to consider thumb encodings.

Based on Evan's suggestion without a commitable test.

llvm-svn: 160441

1 files changed, 11 insertions, 4 deletions

diff --git a/llvm/lib/Target/ARM/ARMISelLowering.cpp b/llvm/lib/Target/ARM/ARMISelLowering.cpp
index 6094811caa5..04370c095cd 100644
--- a/llvm/lib/Target/ARM/ARMISelLowering.cpp
+++ b/llvm/lib/Target/ARM/ARMISelLowering.cpp
@@ -9046,12 +9046,19 @@ bool ARMTargetLowering::isLegalICmpImmediate(int64_t Imm) const {
   return Imm >= 0 && Imm <= 255;
 }
 
-/// isLegalAddImmediate - Return true if the specified immediate is legal
-/// add immediate, that is the target has add instructions which can add
-/// a register with the immediate without having to materialize the
+/// isLegalAddImmediate - Return true if the specified immediate is a legal add
+/// *or sub* immediate, that is the target has add or sub instructions which can
+/// add a register with the immediate without having to materialize the
 /// immediate into a register.
 bool ARMTargetLowering::isLegalAddImmediate(int64_t Imm) const {
-  return ARM_AM::getSOImmVal(Imm) != -1;
+  // Same encoding for add/sub, just flip the sign.
+  int64_t AbsImm = llvm::abs64(Imm);
+  if (!Subtarget->isThumb())
+    return ARM_AM::getSOImmVal(AbsImm) != -1;
+  if (Subtarget->isThumb2())
+    return ARM_AM::getT2SOImmVal(AbsImm) != -1;
+  // Thumb1 only has 8-bit unsigned immediate.
+  return AbsImm >= 0 && AbsImm <= 255;
 }
 
 static bool getARMIndexedAddressParts(SDNode *Ptr, EVT VT,