[PATCH] D37034: Insert IMPLICIT_DEFS for undef uses in tail merging

[Krzysztof Parzyszek via Phabricator via llvm-commits]

kparzysz added inline comments.


================
Comment at: lib/CodeGen/BranchFolding.cpp:379
+      LiveOuts.clear();
+      LiveOuts.addLiveOuts(*Pred);
 
----------------
This needs to calculate liveouts with the tail removed.

This testcase still fails:

```
# RUN: llc -march=hexagon -run-pass branch-folder %s -o - 
---
name: fred
tracksRegLiveness: true

body: |
  bb.0:
    successors: %bb.1, %bb.2
      J2_jumpt undef %p0, %bb.2, implicit-def %pc
      J2_jump %bb.1, implicit-def %pc

  bb.1:
    successors: %bb.3
      %r1 = A2_tfrsi 1
      PS_storerhabs 0, undef %r0
      %r0 = A2_tfrsi 1
      J2_jump %bb.3, implicit-def %pc

  bb.2:
    successors: %bb.3
      %r0 = L2_loadruh_io undef %r1, 0
      PS_storerhabs 0, killed %r0
      %r0 = A2_tfrsi 1
      J2_jump %bb.3, implicit-def %pc

  bb.3:
      PS_jmpret killed %r31, implicit undef %r0, implicit-def %pc
...
```

The output is

```
body:             |
  bb.0:
    successors: %bb.1(0x40000000), %bb.2(0x40000000)
  
    J2_jumpt undef %p0, %bb.2, implicit-def %pc
  
  bb.1:
    successors: %bb.3(0x80000000)
  
    %r1 = A2_tfrsi 1
    J2_jump %bb.3, implicit-def %pc
  
  bb.2:
    successors: %bb.3(0x80000000)
  
    %r0 = L2_loadruh_io undef %r1, 0
  
  bb.3:
    liveins: %r0
  
    PS_storerhabs 0, killed %r0
    %r0 = A2_tfrsi 1
    PS_jmpret killed %r31, implicit undef %r0, implicit-def %pc

...
```

The path `bb.0` -> `bb.1` -> `bb.3` does not define `r0`, but `r0` is a live-in to `bb.3`.


Repository:
  rL LLVM

https://reviews.llvm.org/D37034