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94e52ce7ad
Summary: It seems that negative offset was accidentally allowed in D17967. AFAICT small negative offset should be valid (always raise segfault) on all archs that I'm aware of (especially x86, which is the only one with this optimization enabled) and such case can be useful when loading hiden metadata from an object. However, like the positive side, it should only be done within a certain limit. For now, use the same limit on the positive side for the negative side. A separate option can be added if needs appear. Reviewers: mcrosier, skatkov Reviewed By: skatkov Subscribers: sanjoy, llvm-commits Differential Revision: https://reviews.llvm.org/D38925 llvm-svn: 315991
113 lines
2.6 KiB
LLVM
113 lines
2.6 KiB
LLVM
; RUN: llc -mtriple=x86_64-apple-macosx -O3 -debug-only=faultmaps -enable-implicit-null-checks < %s 2>&1 | FileCheck %s
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; REQUIRES: asserts
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; List cases where we should *not* be emitting implicit null checks.
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; CHECK-NOT: Fault Map Output
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define i32 @imp_null_check_load(i32* %x, i32* %y) {
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entry:
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%c = icmp eq i32* %x, null
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; It isn't legal to move the load from %x from "not_null" to here --
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; the store to %y could be aliasing it.
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br i1 %c, label %is_null, label %not_null, !make.implicit !0
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is_null:
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ret i32 42
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not_null:
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store i32 0, i32* %y
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%t = load i32, i32* %x
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ret i32 %t
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}
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define i32 @imp_null_check_gep_load(i32* %x) {
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entry:
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%c = icmp eq i32* %x, null
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br i1 %c, label %is_null, label %not_null, !make.implicit !0
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is_null:
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ret i32 42
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not_null:
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; null + 5000 * sizeof(i32) lies outside the null page and hence the
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; load to %t cannot be assumed to be reliably faulting.
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%x.gep = getelementptr i32, i32* %x, i32 5000
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%t = load i32, i32* %x.gep
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ret i32 %t
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}
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define i32 @imp_null_check_neg_gep_load(i32* %x) {
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entry:
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%c = icmp eq i32* %x, null
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br i1 %c, label %is_null, label %not_null, !make.implicit !0
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is_null:
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ret i32 42
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not_null:
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; null - 5000 * sizeof(i32) lies outside the null page and hence the
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; load to %t cannot be assumed to be reliably faulting.
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%x.gep = getelementptr i32, i32* %x, i32 -5000
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%t = load i32, i32* %x.gep
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ret i32 %t
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}
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define i32 @imp_null_check_load_no_md(i32* %x) {
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; This is fine, except it is missing the !make.implicit metadata.
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entry:
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%c = icmp eq i32* %x, null
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br i1 %c, label %is_null, label %not_null
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is_null:
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ret i32 42
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not_null:
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%t = load i32, i32* %x
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ret i32 %t
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}
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define i32 @imp_null_check_no_hoist_over_acquire_load(i32* %x, i32* %y) {
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; We cannot hoist %t1 over %t0 since %t0 is an acquire load
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entry:
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%c = icmp eq i32* %x, null
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br i1 %c, label %is_null, label %not_null, !make.implicit !0
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is_null:
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ret i32 42
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not_null:
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%t0 = load atomic i32, i32* %y acquire, align 4
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%t1 = load i32, i32* %x
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%p = add i32 %t0, %t1
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ret i32 %p
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}
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define i32 @imp_null_check_add_result(i32* %x, i32* %y) {
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; This will codegen to:
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;
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; movl (%rsi), %eax
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; addl (%rdi), %eax
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;
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; The load instruction we wish to hoist is the addl, but there is a
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; write-after-write hazard preventing that from happening. We could
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; get fancy here and exploit the commutativity of addition, but right
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; now -implicit-null-checks isn't that smart.
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;
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entry:
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%c = icmp eq i32* %x, null
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br i1 %c, label %is_null, label %not_null, !make.implicit !0
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is_null:
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ret i32 42
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not_null:
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%t0 = load i32, i32* %y
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%t1 = load i32, i32* %x
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%p = add i32 %t0, %t1
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ret i32 %p
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}
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!0 = !{}
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