[DebugInfo] Examine all uses of isDebugValue() for debug instructions.

Because we create a new kind of debug instruction, DBG_LABEL, we need to
check all passes which use isDebugValue() to check MachineInstr is debug
instruction or not. When expelling debug instructions, we should expel
both DBG_VALUE and DBG_LABEL. So, I create a new function,
isDebugInstr(), in MachineInstr to check whether the MachineInstr is
debug instruction or not.

This patch has no new test case. I have run regression test and there is
no difference in regression test.

Differential Revision: https://reviews.llvm.org/D45342

Patch by Hsiangkai Wang.

llvm-svn: 331844
diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyExplicitLocals.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyExplicitLocals.cpp
index cf14643..caf12a6 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyExplicitLocals.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyExplicitLocals.cpp
@@ -231,7 +231,7 @@
       MachineInstr &MI = *I++;
       assert(!WebAssembly::isArgument(MI));
 
-      if (MI.isDebugValue() || MI.isLabel())
+      if (MI.isDebugInstr() || MI.isLabel())
         continue;
 
       // Replace tee instructions with tee_local. The difference is that tee
@@ -375,7 +375,7 @@
   // Assert that all registers have been stackified at this point.
   for (const MachineBasicBlock &MBB : MF) {
     for (const MachineInstr &MI : MBB) {
-      if (MI.isDebugValue() || MI.isLabel())
+      if (MI.isDebugInstr() || MI.isLabel())
         continue;
       for (const MachineOperand &MO : MI.explicit_operands()) {
         assert(