llvm/test/Transforms/DeadStoreElimination/fence.ll

; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 6
; RUN: opt -S -passes=dse < %s | FileCheck %s

; We conservative choose to prevent dead store elimination
; across release or stronger fences.  It's not required
; (since the must still be a race on %addd.i), but
; it is conservatively correct.  A legal optimization
; could hoist the second store above the fence, and then
; DSE one of them.
define void @test1(ptr %addr.i) {
; CHECK-LABEL: define void @test1(
; CHECK-SAME: ptr [[ADDR_I:%.*]]) {
; CHECK-NEXT:    store i32 5, ptr [[ADDR_I]], align 4
; CHECK-NEXT:    fence release
; CHECK-NEXT:    store i32 5, ptr [[ADDR_I]], align 4
; CHECK-NEXT:    ret void
;
  store i32 5, ptr %addr.i, align 4
  fence release
  store i32 5, ptr %addr.i, align 4
  ret void
}

; Same as previous, but with different values.  If we ever optimize
; this more aggressively, this allows us to check that the correct
; store is retained (the 'i32 1' store in this case)
define void @test1b(ptr %addr.i) {
; CHECK-LABEL: define void @test1b(
; CHECK-SAME: ptr [[ADDR_I:%.*]]) {
; CHECK-NEXT:    store i32 42, ptr [[ADDR_I]], align 4
; CHECK-NEXT:    fence release
; CHECK-NEXT:    store i32 1, ptr [[ADDR_I]], align 4
; CHECK-NEXT:    ret void
;
  store i32 42, ptr %addr.i, align 4
  fence release
  store i32 1, ptr %addr.i, align 4
  ret void
}

; We *could* DSE across this fence, but don't.  No other thread can
; observe the order of the acquire fence and the store.
define void @test2(ptr %addr.i) {
; CHECK-LABEL: define void @test2(
; CHECK-SAME: ptr [[ADDR_I:%.*]]) {
; CHECK-NEXT:    store i32 5, ptr [[ADDR_I]], align 4
; CHECK-NEXT:    fence acquire
; CHECK-NEXT:    store i32 5, ptr [[ADDR_I]], align 4
; CHECK-NEXT:    ret void
;
  store i32 5, ptr %addr.i, align 4
  fence acquire
  store i32 5, ptr %addr.i, align 4
  ret void
}

; We DSE stack alloc'ed and byval locations, in the presence of fences.
; Fence does not make an otherwise thread local store visible.
; Right now the DSE in presence of fence is only done in end blocks (with no successors),
; but the same logic applies to other basic blocks as well.
; The store to %addr.i can be removed since it is a byval attribute
define void @test3(ptr byval(i32) %addr.i) {
; CHECK-LABEL: define void @test3(
; CHECK-SAME: ptr byval(i32) [[ADDR_I:%.*]]) {
; CHECK-NEXT:    fence release
; CHECK-NEXT:    ret void
;
  store i32 5, ptr %addr.i, align 4
  fence release
  ret void
}

declare void @foo(ptr nocapture %p)

declare noalias ptr @malloc(i32)

; DSE of stores in locations allocated through library calls.
define void @test_nocapture() {
; CHECK-LABEL: define void @test_nocapture() {
; CHECK-NEXT:    [[M:%.*]] = call ptr @malloc(i32 24)
; CHECK-NEXT:    call void @foo(ptr [[M]])
; CHECK-NEXT:    fence release
; CHECK-NEXT:    ret void
;
  %m  =  call ptr @malloc(i32 24)
  call void @foo(ptr %m)
  store i8 4, ptr %m
  fence release
  ret void
}

; This is a full fence, but it does not make a thread local store visible.
; We can DSE the store in presence of the fence.
define void @fence_seq_cst() {
; CHECK-LABEL: define void @fence_seq_cst() {
; CHECK-NEXT:    fence seq_cst
; CHECK-NEXT:    ret void
;
  %P1 = alloca i32
  store i32 0, ptr %P1, align 4
  fence seq_cst
  store i32 4, ptr %P1, align 4
  ret void
}