Do not track subregister liveness when it brings no benefits

Some subregisters are only to indicate different access sizes, while not
providing any way to actually divide the register up into multiple
disjunct parts. Avoid tracking subregister liveness in these cases as it
is not beneficial.

Differential Revision: http://reviews.llvm.org/D8429

llvm-svn: 232695

1 files changed, 2 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/MachineVerifier.cpp b/llvm/lib/CodeGen/MachineVerifier.cpp
index d39733be6c4..22990e3d5d7 100644
--- a/llvm/lib/CodeGen/MachineVerifier.cpp
+++ b/llvm/lib/CodeGen/MachineVerifier.cpp
@@ -1573,7 +1573,8 @@ void MachineVerifier::verifyLiveRangeSegment(const LiveRange &LR,
       if (!hasRead) {
         // When tracking subregister liveness, the main range must start new
         // values on partial register writes, even if there is no read.
-        if (!MRI->tracksSubRegLiveness() || LaneMask != 0 || !hasSubRegDef) {
+        if (!MRI->shouldTrackSubRegLiveness(Reg) || LaneMask != 0 ||
+            !hasSubRegDef) {
           report("Instruction ending live segment doesn't read the register",
                  MI);
           errs() << S << " in " << LR << '\n';