[ARM] GlobalISel: Select add i32, i32

Add the minimal support necessary to select a function that returns the sum of
two i32 values.

This includes some support for argument/return lowering of i32 values through
registers, as well as the handling of copy and add instructions throughout the
GlobalISel pipeline.

Differential Revision: https://reviews.llvm.org/D26677

llvm-svn: 289940

1 files changed, 5 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/GlobalISel/InstructionSelector.cpp b/llvm/lib/CodeGen/GlobalISel/InstructionSelector.cpp
index 9149864817c..3b2177c72c4 100644
--- a/llvm/lib/CodeGen/GlobalISel/InstructionSelector.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/InstructionSelector.cpp
@@ -43,6 +43,11 @@ bool InstructionSelector::constrainSelectedInstRegOperands(
     if (TRI.isPhysicalRegister(MO.getReg()))
       continue;
 
+    // Register operands with a value of 0 (e.g. predicate operands) don't need
+    // to be constrained.
+    if (MO.getReg() == 0)
+      continue;
+
     const TargetRegisterClass *RC = TII.getRegClass(I.getDesc(), OpI, &TRI, MF);
     assert(RC && "Selected inst should have regclass operand");