Sander de Smalen bae8f1336d
Reland "RegisterCoalescer: Add implicit-def of super register when coalescing SUBREG_TO_REG" (#134408)
This tries to reland #123632 (previously reverted by commit
6b1db79887df19bc8e8c946108966aa6021c8b87)

This PR aims to fix coalescing of SUBREG_TO_REG when sub-register
liveness tracking is enabled and this is now the so-manieth
reincarnation of this effort :)

This change is needed in order to enable subreg liveness tracking for 
AArch64, because without the implicit-def, Machine Copy Propagation
would remove a 'redundant' copy because it doesn't realise that the 
top 32-bits of the register are zeroed, which subsequent instructions
rely on. 

Changes compared to previous PR: 

* Rather than updating all instructions that define the source register
(SrcReg) of the SUBREG_TO_REG, this new approach only updates
instructions
that define SrcReg when they dominate the SUBREG_TO_REG. The live-ranges
  are updated accordingly.
2025-07-30 14:42:24 +01:00
..
2025-05-22 15:42:22 +01:00
2023-02-14 10:25:24 -04:00