[X86] Call removeDeadNode when we're done doing custom isel for mul, div and test

Summary:
Once we've done our custom isel for these nodes, I think we should be calling removeDeadNode to prune them out of the DAG. Table driven isel ultimately either calls morphNodeTo which modifies a node and doesn't leave dead nodes. Or it emits new nodes and then calls removeDeadNode as part of Opc_CompleteMatch.

If you run a simple multiply test case like this through llc with -debug you'll see a umul_lohi node get printed as part of the dump for Instruction Selection ends.

```
define i64 @foo(i64 %a, i64 %b) local_unnamed_addr #0 {
entry:
  %conv = zext i64 %a to i128
  %conv1 = zext i64 %b to i128
  %mul = mul nuw nsw i128 %conv1, %conv
  %shr = lshr i128 %mul, 64
  %conv2 = trunc i128 %shr to i64
  ret i64 %conv2
}
```

Reviewers: RKSimon, spatel, zvi, guyblank, niravd

Reviewed By: niravd

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D37547

llvm-svn: 312857

0 files changed, 0 insertions, 0 deletions