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/atomic-ops.ll b/llvm/test/CodeGen/AArch64/atomic-ops.ll
index 58b5d1d..36d0eda 100644
--- a/llvm/test/CodeGen/AArch64/atomic-ops.ll
+++ b/llvm/test/CodeGen/AArch64/atomic-ops.ll
@@ -889,8 +889,7 @@
; function there.
; CHECK-NEXT: cmp w[[OLD]], w0
; CHECK-NEXT: b.ne [[GET_OUT:.LBB[0-9]+_[0-9]+]]
- ; As above, w1 is a reasonable guess.
-; CHECK: stxrb [[STATUS:w[0-9]+]], w1, [x[[ADDR]]]
+; CHECK: stxrb [[STATUS:w[0-9]+]], {{w[0-9]+}}, [x[[ADDR]]]
; CHECK-NEXT: cbnz [[STATUS]], [[STARTAGAIN]]
; CHECK-NOT: dmb
@@ -911,8 +910,7 @@
; function there.
; CHECK-NEXT: cmp w[[OLD]], w0
; CHECK-NEXT: b.ne [[GET_OUT:.LBB[0-9]+_[0-9]+]]
- ; As above, w1 is a reasonable guess.
-; CHECK: stlxrh [[STATUS:w[0-9]+]], w1, [x[[ADDR]]]
+; CHECK: stlxrh [[STATUS:w[0-9]+]], {{w[0-9]+}}, [x[[ADDR]]]
; CHECK-NEXT: cbnz [[STATUS]], [[STARTAGAIN]]
; CHECK-NOT: dmb
@@ -933,8 +931,7 @@
; function there.
; CHECK-NEXT: cmp w[[OLD]], w0
; CHECK-NEXT: b.ne [[GET_OUT:.LBB[0-9]+_[0-9]+]]
- ; As above, w1 is a reasonable guess.
-; CHECK: stlxr [[STATUS:w[0-9]+]], w1, [x[[ADDR]]]
+; CHECK: stlxr [[STATUS:w[0-9]+]], {{w[0-9]+}}, [x[[ADDR]]]
; CHECK-NEXT: cbnz [[STATUS]], [[STARTAGAIN]]
; CHECK-NOT: dmb