tree e0bed919d73d6ada7298ff5f2abee75ab28f8fd3
parent 7f5bf77c657719f6f305139f7dd6d1871f4041e5
author Ryan Buchner <92571492+bababuck@users.noreply.github.com> 1746469056 -0700
committer GitHub <noreply@github.com> 1746469056 +0200
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[AMDGPU] Remove implicit definition of register group when restoring the last sub-register after a spill (#133986)

Extension of https://reviews.llvm.org/D141101 to remove the define flag
from the last stack memory access. Fixes case where COPY instructions
are used for some of the stack restoration, but the copies get optimized
away during the machine-cp pass.

Prior to this change, was possible to produce the following code:
$agpr16_agpr17_agpr18_agpr19 = SCRATCH_LOAD_DWORDX4_ST 64, 0, implicit
$exec, implicit $flat_scr, implicit-def
$agpr16_agpr17_agpr18_agpr19_agpr20_agpr21_agpr22_agpr23_agpr24_agpr25_agpr26_agpr27_agpr28_agpr29_agpr30_agpr31
:: (load (s128) from %stack.17, align 4, addrspace 5)
$agpr20_agpr21_agpr22_agpr23 = SCRATCH_LOAD_DWORDX4_ST 80, 0, implicit
$exec, implicit $flat_scr :: (load (s128) from %stack.17 + 16, align 4,
addrspace 5)
$agpr24_agpr25_agpr26_agpr27 = SCRATCH_LOAD_DWORDX4_ST 96, 0, implicit
$exec, implicit $flat_scr :: (load (s128) from %stack.17 + 32, align 4,
addrspace 5)
$agpr31 = COPY $agpr112, implicit
$agpr16_agpr17_agpr18_agpr19_agpr20_agpr21_agpr22_agpr23_agpr24_agpr25_agpr26_agpr27_agpr28_agpr29_agpr30_agpr31
$agpr30 = COPY $agpr208, implicit
$agpr16_agpr17_agpr18_agpr19_agpr20_agpr21_agpr22_agpr23_agpr24_agpr25_agpr26_agpr27_agpr28_agpr29_agpr30_agpr31
$agpr28_agpr29 = SCRATCH_LOAD_DWORDX2_ST 112, 0, implicit $exec,
implicit $flat_scr, implicit-def
$agpr16_agpr17_agpr18_agpr19_agpr20_agpr21_agpr22_agpr23_agpr24_agpr25_agpr26_agpr27_agpr28_agpr29_agpr30_agpr31
:: (load (s64) from %stack.17 + 48, align 4, addrspace 5)

where `$agpr30 = COPY $agpr208` would be optimized away by `machine-cp`
pass. Instead, change to:
$agpr28_agpr29 = SCRATCH_LOAD_DWORDX2_ST 112, 0, implicit $exec,
implicit $flat_scr :: (load (s64) from %stack.17 + 48, align 4,
addrspace 5)

Fixes #131386.

Made the simple fix, but I'm not completely comfortable with this change
since the reason for the previous inclusion of `IsLastSubReg` is unclear
to me.

@krzysz00