https://llvm.org/bugs/show_bug.cgi?id=25457
Bug ID: 25457
Summary: [AArch64] Aliases of WZR/XZR are not considered
constant
Product: libraries
Version: trunk
Hardware: PC
OS: Windows NT
Status: NEW
Severity: normal
Priority: P
Component: Backend: AArch64
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected], [email protected],
[email protected], [email protected]
Classification: Unclassified
The alias registers of WZR/XZR are WZR_W0, W30_WZR, LR_XZR, and XZR_X0. None
of these aliases are marked as constant, so WZR/XZR is not considered as
constant.
The %wzr_w0 alias was added here:
http://reviews.llvm.org/rL238818
One practical implication is that in passes such as machine-cse and
machine-sink an instruction such as %v = copy %wzr cannot be moved because llvm
thinks %wzr is not a constant physical register.
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