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3bb84c9bcc
The C and C++ semantics for compare_exchange require it to return a bool
indicating success. This gets mapped to LLVM IR which follows each cmpxchg with
an icmp of the value loaded against the desired value.
When lowered to ldxr/stxr loops, this extra comparison is redundant: its
results are implicit in the control-flow of the function.
This commit makes two changes: it replaces that icmp with appropriate PHI
nodes, and then makes sure earlyCSE is called after expansion to actually make
use of the opportunities revealed.
I've also added -{arm,aarch64}-enable-atomic-tidy options, so that
existing fragile tests aren't perturbed too much by the change. Many
of them either rely on undef/unreachable too pervasively to be
restored to something well-defined (particularly while making sure
they test the same obscure assert from many years ago), or depend on a
particular CFG shape, which is disrupted by SimplifyCFG.
rdar://problem/16227836
llvm-svn: 209883
36 lines
930 B
LLVM
36 lines
930 B
LLVM
; RUN: llc -mtriple=aarch64-none-linux-gnu -aarch64-atomic-cfg-tidy=0 -verify-machineinstrs -o - %s | FileCheck %s
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; LLVM should be able to cope with multiple uses of the same flag-setting
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; instruction at different points of a routine. Either by rematerializing the
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; compare or by saving and restoring the flag register.
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declare void @bar()
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@var = global i32 0
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define i32 @test_multiflag(i32 %n, i32 %m, i32 %o) {
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; CHECK-LABEL: test_multiflag:
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%test = icmp ne i32 %n, %m
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; CHECK: cmp [[LHS:w[0-9]+]], [[RHS:w[0-9]+]]
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%val = zext i1 %test to i32
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; CHECK: cset {{[xw][0-9]+}}, ne
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store i32 %val, i32* @var
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call void @bar()
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; CHECK: bl bar
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; Currently, the comparison is emitted again. An MSR/MRS pair would also be
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; acceptable, but assuming the call preserves NZCV is not.
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br i1 %test, label %iftrue, label %iffalse
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; CHECK: cmp [[LHS]], [[RHS]]
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; CHECK: b.eq
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iftrue:
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ret i32 42
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iffalse:
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ret i32 0
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}
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