[ARM] GlobalISel: Select G_CONSTANT with CImm operands

When selecting a G_CONSTANT to a MOVi, we need the value to be an Imm
operand. We used to just leave the G_CONSTANT operand unchanged, which
works in some cases (such as the GEP offsets that we create when
referring to stack slots). However, in many other places the G_CONSTANTs
are created with CImm operands. This patch makes sure to handle those as
well, and to error out gracefully if in the end we don't end up with an
Imm operand.

Thanks to Oliver Stannard for reporting this issue.

llvm-svn: 301162

1 files changed, 12 insertions, 0 deletions

diff --git a/llvm/lib/Target/ARM/ARMInstructionSelector.cpp b/llvm/lib/Target/ARM/ARMInstructionSelector.cpp
index 3b62c3878c3..a99dc159d11 100644
--- a/llvm/lib/Target/ARM/ARMInstructionSelector.cpp
+++ b/llvm/lib/Target/ARM/ARMInstructionSelector.cpp
@@ -351,6 +351,18 @@ bool ARMInstructionSelector::select(MachineInstr &I) const {
            "Expected constant to live in a GPR");
     I.setDesc(TII.get(ARM::MOVi));
     MIB.add(predOps(ARMCC::AL)).add(condCodeOp());
+
+    auto &Val = I.getOperand(1);
+    if (Val.isCImm()) {
+      if (Val.getCImm()->getBitWidth() > 32)
+        return false;
+      Val.ChangeToImmediate(Val.getCImm()->getZExtValue());
+    }
+
+    if (!Val.isImm()) {
+      return false;
+    }
+
     break;
   }
   case G_STORE: