Allow negative immediates in ARM and Thumb2 compares.

ARM and Thumb2 mode can use cmn instructions to compare against negative
immediates. Thumb1 mode can't.

llvm-svn: 154183

1 files changed, 4 insertions, 2 deletions

diff --git a/llvm/lib/Target/ARM/ARMISelLowering.cpp b/llvm/lib/Target/ARM/ARMISelLowering.cpp
index fab3e24551b..c20ee674ce8 100644
--- a/llvm/lib/Target/ARM/ARMISelLowering.cpp
+++ b/llvm/lib/Target/ARM/ARMISelLowering.cpp
@@ -8614,10 +8614,12 @@ bool ARMTargetLowering::isLegalAddressingMode(const AddrMode &AM,
 /// a register against the immediate without having to materialize the
 /// immediate into a register.
 bool ARMTargetLowering::isLegalICmpImmediate(int64_t Imm) const {
+  // Thumb2 and ARM modes can use cmn for negative immediates.
   if (!Subtarget->isThumb())
-    return ARM_AM::getSOImmVal(Imm) != -1;
+    return ARM_AM::getSOImmVal(std::abs(Imm)) != -1;
   if (Subtarget->isThumb2())
-    return ARM_AM::getT2SOImmVal(Imm) != -1;
+    return ARM_AM::getT2SOImmVal(std::abs(Imm)) != -1;
+  // Thumb1 doesn't have cmn, and only 8-bit immediates.
   return Imm >= 0 && Imm <= 255;
 }