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6484d69f76
We can remove dead stores in the presence of fence instructions. Fence does not change an otherwise thread local store to visible. reviewers: reames, dexonsmith, jfb Differential Revision: http://reviews.llvm.org/D22001 llvm-svn: 274795
97 lines
2.5 KiB
LLVM
97 lines
2.5 KiB
LLVM
; RUN: opt -S -basicaa -dse < %s | FileCheck %s
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; We conservative choose to prevent dead store elimination
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; across release or stronger fences. It's not required
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; (since the must still be a race on %addd.i), but
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; it is conservatively correct. A legal optimization
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; could hoist the second store above the fence, and then
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; DSE one of them.
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define void @test1(i32* %addr.i) {
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; CHECK-LABEL: @test1
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; CHECK: store i32 5
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; CHECK: fence
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; CHECK: store i32 5
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; CHECK: ret
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store i32 5, i32* %addr.i, align 4
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fence release
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store i32 5, i32* %addr.i, align 4
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ret void
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}
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; Same as previous, but with different values. If we ever optimize
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; this more aggressively, this allows us to check that the correct
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; store is retained (the 'i32 1' store in this case)
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define void @test1b(i32* %addr.i) {
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; CHECK-LABEL: @test1b
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; CHECK: store i32 42
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; CHECK: fence release
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; CHECK: store i32 1
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; CHECK: ret
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store i32 42, i32* %addr.i, align 4
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fence release
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store i32 1, i32* %addr.i, align 4
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ret void
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}
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; We *could* DSE across this fence, but don't. No other thread can
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; observe the order of the acquire fence and the store.
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define void @test2(i32* %addr.i) {
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; CHECK-LABEL: @test2
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; CHECK: store
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; CHECK: fence
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; CHECK: store
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; CHECK: ret
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store i32 5, i32* %addr.i, align 4
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fence acquire
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store i32 5, i32* %addr.i, align 4
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ret void
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}
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; We DSE stack alloc'ed and byval locations, in the presence of fences.
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; Fence does not make an otherwise thread local store visible.
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; Right now the DSE in presence of fence is only done in end blocks (with no successors),
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; but the same logic applies to other basic blocks as well.
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; The store to %addr.i can be removed since it is a byval attribute
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define void @test3(i32* byval %addr.i) {
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; CHECK-LABEL: @test3
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; CHECK-NOT: store
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; CHECK: fence
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; CHECK: ret
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store i32 5, i32* %addr.i, align 4
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fence release
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ret void
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}
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declare void @foo(i8* nocapture %p)
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declare noalias i8* @malloc(i32)
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; DSE of stores in locations allocated through library calls.
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define void @test_nocapture() {
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; CHECK-LABEL: @test_nocapture
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; CHECK: malloc
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; CHECK: foo
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; CHECK-NOT: store
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; CHECK: fence
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%m = call i8* @malloc(i32 24)
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call void @foo(i8* %m)
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store i8 4, i8* %m
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fence release
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ret void
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}
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; This is a full fence, but it does not make a thread local store visible.
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; We can DSE the store in presence of the fence.
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define void @fence_seq_cst() {
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; CHECK-LABEL: @fence_seq_cst
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; CHECK-NEXT: fence seq_cst
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; CHECK-NEXT: ret void
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%P1 = alloca i32
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store i32 0, i32* %P1, align 4
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fence seq_cst
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store i32 4, i32* %P1, align 4
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ret void
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}
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