[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:
> 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
> 
> ...
> 
> ```
For some reason this failure only manifests further up the stack of patches 


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

https://reviews.llvm.org/D156345