[DAGCombiner] add missing folds for scalar select of {-1,0,1}

The motivation for filling out these select-of-constants cases goes back to D24480, 
where we discussed removing an IR fold from add(zext) --> select. And that goes back to:
https://reviews.llvm.org/rL75531
https://reviews.llvm.org/rL159230

The idea is that we should always canonicalize patterns like this to a select-of-constants 
in IR because that's the smallest IR and the best for value tracking. Note that we currently 
do the opposite in some cases (like the cases in *this* patch). Ie, the proposed folds in 
this patch already exist in InstCombine today:
https://github.com/llvm-mirror/llvm/blob/master/lib/Transforms/InstCombine/InstCombineSelect.cpp#L1151

As this patch shows, most targets generate better machine code for simple ext/add/not ops 
rather than a select of constants. So the follow-up steps to make this less of a patchwork 
of special-case folds and missing IR canonicalization:

1. Have DAGCombiner convert any select of constants into ext/add/not ops.
2  Have InstCombine canonicalize in the other direction (create more selects).

Differential Revision: https://reviews.llvm.org/D30180


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@296137 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 1 insertions, 1 deletions

diff --git a/test/CodeGen/NVPTX/add-128bit.ll b/test/CodeGen/NVPTX/add-128bit.ll
index 29e3cdffae7..a077c3fcf89 100644
--- a/test/CodeGen/NVPTX/add-128bit.ll
+++ b/test/CodeGen/NVPTX/add-128bit.ll
@@ -8,7 +8,7 @@ define void @foo(i64 %a, i64 %add, i128* %retptr) {
 ; CHECK:        add.s64
 ; CHECK:        setp.lt.u64
 ; CHECK:        setp.lt.u64
-; CHECK:        selp.b64
+; CHECK:        selp.u64
 ; CHECK:        selp.b64
 ; CHECK:        add.s64
   %t1 = sext i64 %a to i128