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[RegisterCoalescer] Fix subrange update when rematerialization widens a def #151974

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Merged
merged 1 commit into from
Aug 5, 2025
Merged

[RegisterCoalescer] Fix subrange update when rematerialization widens a def #151974

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10 changes: 5 additions & 5 deletions llvm/lib/CodeGen/RegisterCoalescer.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1624,11 +1624,11 @@ bool RegisterCoalescer::reMaterializeTrivialDef(const CoalescerPair &CP,
UpdatedSubRanges = true;
} else {
// We know that this lane is defined by this instruction,
// but at this point it may be empty because it is not used by
// anything. This happens when updateRegDefUses adds the missing
// lanes. Assign that lane a dead def so that the interferences
// are properly modeled.
if (SR.empty())
// but at this point it might not be live because it was not defined
// by the original instruction. This happens when the
// rematerialization widens the defined register. Assign that lane a
// dead def so that the interferences are properly modeled.
if (!SR.liveAt(DefIndex))
SR.createDeadDef(DefIndex, Alloc);
}
}
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25 changes: 25 additions & 0 deletions llvm/test/CodeGen/SystemZ/regcoal-subranges-update-remat.mir
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Expand Up @@ -43,3 +43,28 @@ body: |
%3:gr32bit = COPY killed %1
Return implicit %3
...

---
name: test_dead_at_remat_later_defined
tracksRegLiveness: true
body: |
bb.0:
; CHECK-LABEL: name: test_dead_at_remat_later_defined
; CHECK: undef [[LHI:%[0-9]+]].subreg_l32:gr128bit = LHI 0
; CHECK-NEXT: [[LHI:%[0-9]+]].subreg_l64:gr128bit = LGHI 2
; CHECK-NEXT: [[LHI1:%[0-9]+]]:gr32bit = LHI 1
; CHECK-NEXT: [[LHI:%[0-9]+]].subreg_lh32:gr128bit = COPY [[LHI1]]
; CHECK-NEXT: [[LGHI:%[0-9]+]]:gr64bit = LGHI 2
; CHECK-NEXT: [[LHI:%[0-9]+]].subreg_h32:gr128bit = COPY [[LGHI]].subreg_l32
; CHECK-NEXT: $r0q = COPY [[LHI]]
; CHECK-NEXT: $r4d = COPY [[LGHI]].subreg_h32
%0:gr64bit = LGHI 2
%1:gr32bit = LHI 0
%2:gr32bit = LHI 1
undef %3.subreg_ll32:gr128bit = COPY %0.subreg_l32
%3.subreg_lh32:gr128bit = COPY %2
%3.subreg_l32:gr128bit = COPY %1
%3.subreg_h32:gr128bit = COPY %0.subreg_l32
$r0q = COPY %3
$r4d = COPY %0.subreg_h32
...