[PATCH] D156345: RegisterCoalescer: Add implicit-def of super register when coalescing SUBREG_TO_REG

[Matt Arsenault via Phabricator via llvm-commits]

arsenm added inline comments.


================
Comment at: llvm/lib/CodeGen/RegisterCoalescer.cpp:2163
+  if (CP.getDstIdx()) {
+    assert(!IsSubregToReg && "can this happen?");
+    updateRegDefsUses(CP.getDstReg(), CP.getDstReg(), CP.getDstIdx(), false);
----------------
arsenm wrote:
> qcolombet wrote:
> > qcolombet wrote:
> > > Maybe it can happen if you have something like:
> > > ```
> > > %a = SUBREG_TO_REG ...
> > > %b = IMPLICIT_DEF
> > > %c = INSERT_SUBREG %b, %a, sub
> > > ```
> > > =>
> > > ```
> > > %a = SUBREG_TO_REG ...
> > > %c.sub = COPY %a
> > > ```
> > > =>
> > > ```
> > > %c.sub = SUBREG_TO_REG ...
> > > ```
> > Ditto on the can this happen.
> > Did you give a try to the example I gave?
> If I force subregister liveness on ninja check does find the failures.
> 
> Also the baseline ninja check with verify-coalescing forced on isn't clean :(
This does hit the assert / verifier error, so I'll push it somewhere

```

# RUN: llc -mtriple=x86_64-- -run-pass=register-coalescer -enable-subreg-liveness -o - %s
---
name:            test
tracksRegLiveness: true
body:             |
  bb.0:
    liveins: $eax
    %init_eax:gr32 = COPY $eax
    %a:gr64 = SUBREG_TO_REG 0, %init_eax, %subreg.sub_32bit
    %b:gr32 = IMPLICIT_DEF
    %c:gr64 = INSERT_SUBREG %a, %b, %subreg.sub_32bit
    JCC_1 %bb.2, 4, implicit undef $eflags

  bb.1:
    %imm0:gr32 = MOV32r0 implicit-def dead $eflags
    %a = SUBREG_TO_REG 0, %imm0, %subreg.sub_32bit
    %c.sub_32bit = COPY %a

  bb.2:
    %c.sub_32bit = SUBREG_TO_REG %a, %b, %subreg.sub_32bit
    RET 0, implicit %c

...

```


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D156345/new/

https://reviews.llvm.org/D156345