R600: Add carry and borrow instructions. Use them to implement UADDO/USUBO

v2: tighten the sub64 tests
v3: rename to CARRY/BORROW
v4: fixup test cmdline
    add known bits computation
    use sign extend instead of sub 0,x
    better add test
v5: remove redundant break
    move lowering to separate functions
    fix comments

Signed-off-by: Jan Vesely <jan.vesely@rutgers.edu>
Reviewers: arsenm

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@234759 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/R600/AMDGPUISelLowering.cpp

@@ -2763,6 +2763,12 @@ void AMDGPUTargetLowering::computeKnownBitsForTargetNode(
                               KnownZero, KnownOne, DAG, Depth);
     break;
 
+  case AMDGPUISD::CARRY:
+  case AMDGPUISD::BORROW: {
+    KnownZero = APInt::getHighBitsSet(32, 31);
+    break;
+  }
+
   case AMDGPUISD::BFE_I32:
   case AMDGPUISD::BFE_U32: {
     ConstantSDNode *CWidth = dyn_cast<ConstantSDNode>(Op.getOperand(2));
@@ -2805,6 +2811,10 @@ unsigned AMDGPUTargetLowering::ComputeNumSignBitsForTargetNode(
     return Width ? 32 - (Width->getZExtValue() & 0x1f) : 1;
   }
 
+  case AMDGPUISD::CARRY:
+  case AMDGPUISD::BORROW:
+    return 31;
+
   default:
     return 1;
   }