ARM & AArch64: make use of common cmpxchg idioms after expansion
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
diff --git a/llvm/test/CodeGen/AArch64/flags-multiuse.ll b/llvm/test/CodeGen/AArch64/flags-multiuse.ll
index c9b0b9f..77bbcdd 100644
--- a/llvm/test/CodeGen/AArch64/flags-multiuse.ll
+++ b/llvm/test/CodeGen/AArch64/flags-multiuse.ll
@@ -1,4 +1,4 @@
-; RUN: llc -mtriple=aarch64-none-linux-gnu -verify-machineinstrs -o - %s | FileCheck %s
+; RUN: llc -mtriple=aarch64-none-linux-gnu -aarch64-atomic-cfg-tidy=0 -verify-machineinstrs -o - %s | FileCheck %s
; LLVM should be able to cope with multiple uses of the same flag-setting
; instruction at different points of a routine. Either by rematerializing the