[llvm-bugs] [Bug 35072] New: [AArch64] cmpxchg not using Armv8.1-a instructions at -O0
llvm-bugs at lists.llvm.org
Wed Oct 25 06:08:06 PDT 2017
Bug ID: 35072
Summary: [AArch64] cmpxchg not using Armv8.1-a instructions at
Component: new bugs
Assignee: unassignedbugs at nondot.org
Reporter: Christof.Douma at arm.com
CC: llvm-bugs at lists.llvm.org
Created attachment 19337
The Armv8.1-a target has a compare-and-swap (CAS) instruction which is used to
implement cmpxchg operation of LLVM IR. However, at -O0 the code generator is
still emitting a long code sequence to emulate this instruction.
LLVM should use CAS even at -O0.
A reproducer that show the behaviour is attached. Compile using:
llc -mattr=+v8.1a cmpxchg.ll -O[0|2]
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