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[LangRef] Adjust guarantee for llvm.memcpy to also allow equal arguments.

Browse Source 
This adjusts the description of `llvm.memcpy` to also allow operands
to be equal. This is in line with what Clang currently expects.

This change is intended to be temporary and followed by re-introduce
a variant with the non-overlapping guarantee for cases where we can
actually ensure that property in the front-end.

See the links below for more details:
http://lists.llvm.org/pipermail/cfe-dev/2020-August/066614.html
and PR11763.

Reviewed By: nikic

Differential Revision: https://reviews.llvm.org/D86815
This commit is contained in:
Florian Hahn 2020-09-04 20:43:28 +01:00
parent 39d0c7029b
commit 6276196b86
8 changed files with 55 additions and 59 deletions
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10
docs/LangRef.rst
View File

@ -12479,11 +12479,11 @@ very cleanly specified and it is unwise to depend on it.
Semantics:
""""""""""
The '``llvm.memcpy.*``' intrinsics copy a block of memory from the
source location to the destination location, which are not allowed to
overlap. It copies "len" bytes of memory over. If the argument is known
to be aligned to some boundary, this can be specified as an attribute on
the argument.
The '``llvm.memcpy.*``' intrinsics copy a block of memory from the source
location to the destination location, which must either be equal or
non-overlapping. It copies "len" bytes of memory over. If the argument is known
to be aligned to some boundary, this can be specified as an attribute on the
argument.
If "len" is 0, the pointers may be NULL, dangling, ``undef``, or ``poison``
pointers. However, they must still be appropriately aligned.

22
lib/Analysis/BasicAliasAnalysis.cpp
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@ -975,22 +975,14 @@ ModRefInfo BasicAAResult::getModRefInfo(const CallBase *Call,
return ModRefInfo::NoModRef;
}
// The semantics of memcpy intrinsics forbid overlap between their respective
// operands, i.e., source and destination of any given memcpy must no-alias.
// If Loc must-aliases either one of these two locations, then it necessarily
// no-aliases the other.
// The semantics of memcpy intrinsics either exactly overlap or do not
// overlap, i.e., source and destination of any given memcpy are either
// no-alias or must-alias.
if (auto *Inst = dyn_cast<AnyMemCpyInst>(Call)) {
AliasResult SrcAA, DestAA;
if ((SrcAA = getBestAAResults().alias(MemoryLocation::getForSource(Inst),
Loc, AAQI)) == MustAlias)
// Loc is exactly the memcpy source thus disjoint from memcpy dest.
return ModRefInfo::Ref;
if ((DestAA = getBestAAResults().alias(MemoryLocation::getForDest(Inst),
Loc, AAQI)) == MustAlias)
// The converse case.
return ModRefInfo::Mod;
AliasResult SrcAA =
getBestAAResults().alias(MemoryLocation::getForSource(Inst), Loc, AAQI);
AliasResult DestAA =
getBestAAResults().alias(MemoryLocation::getForDest(Inst), Loc, AAQI);
// It's also possible for Loc to alias both src and dest, or neither.
ModRefInfo rv = ModRefInfo::NoModRef;
if (SrcAA != NoAlias)

4
test/Analysis/BasicAA/assume.ll
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@ -14,8 +14,8 @@ define void @test1(i8* %P, i8* %Q) nounwind ssp {
; CHECK: MayAlias: i8* %P, i8* %Q
; CHECK: NoModRef: Ptr: i8* %P <-> tail call void @llvm.assume(i1 true)
; CHECK: NoModRef: Ptr: i8* %Q <-> tail call void @llvm.assume(i1 true)
; CHECK: Just Mod: Ptr: i8* %P <-> tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
; CHECK: Just Ref: Ptr: i8* %Q <-> tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
; CHECK: Both ModRef: Ptr: i8* %P <-> tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
; CHECK: Both ModRef: Ptr: i8* %Q <-> tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
; CHECK: NoModRef: tail call void @llvm.assume(i1 true) <-> tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
; CHECK: NoModRef: tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false) <-> tail call void @llvm.assume(i1 true)
}

48
test/Analysis/BasicAA/cs-cs.ll
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@ -17,12 +17,12 @@ define void @test2(i8* %P, i8* %Q) #3 {
; CHECK-LABEL: Function: test2:
; CHECK: MayAlias: i8* %P, i8* %Q
; CHECK: Just Mod: Ptr: i8* %P <-> tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
; CHECK: Just Ref: Ptr: i8* %Q <-> tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
; CHECK: Just Mod: Ptr: i8* %P <-> tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
; CHECK: Just Ref: Ptr: i8* %Q <-> tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
; CHECK: Just Mod: tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false) <-> tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
; CHECK: Just Mod: tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false) <-> tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
; CHECK: Both ModRef: Ptr: i8* %P <-> tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
; CHECK: Both ModRef: Ptr: i8* %Q <-> tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
; CHECK: Both ModRef: Ptr: i8* %P <-> tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
; CHECK: Both ModRef: Ptr: i8* %Q <-> tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
; CHECK: Both ModRef: tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false) <-> tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
; CHECK: Both ModRef: tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false) <-> tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
}
define void @test2_atomic(i8* %P, i8* %Q) #3 {
@ -33,12 +33,12 @@ define void @test2_atomic(i8* %P, i8* %Q) #3 {
; CHECK-LABEL: Function: test2_atomic:
; CHECK: MayAlias: i8* %P, i8* %Q
; CHECK: Just Mod: Ptr: i8* %P <-> tail call void @llvm.memcpy.element.unordered.atomic.p0i8.p0i8.i64(i8* align 1 %P, i8* align 1 %Q, i64 12, i32 1)
; CHECK: Just Ref: Ptr: i8* %Q <-> tail call void @llvm.memcpy.element.unordered.atomic.p0i8.p0i8.i64(i8* align 1 %P, i8* align 1 %Q, i64 12, i32 1)
; CHECK: Just Mod: Ptr: i8* %P <-> tail call void @llvm.memcpy.element.unordered.atomic.p0i8.p0i8.i64(i8* align 1 %P, i8* align 1 %Q, i64 12, i32 1)
; CHECK: Just Ref: Ptr: i8* %Q <-> tail call void @llvm.memcpy.element.unordered.atomic.p0i8.p0i8.i64(i8* align 1 %P, i8* align 1 %Q, i64 12, i32 1)
; CHECK: Just Mod: tail call void @llvm.memcpy.element.unordered.atomic.p0i8.p0i8.i64(i8* align 1 %P, i8* align 1 %Q, i64 12, i32 1) <-> tail call void @llvm.memcpy.element.unordered.atomic.p0i8.p0i8.i64(i8* align 1 %P, i8* align 1 %Q, i64 12, i32 1)
; CHECK: Just Mod: tail call void @llvm.memcpy.element.unordered.atomic.p0i8.p0i8.i64(i8* align 1 %P, i8* align 1 %Q, i64 12, i32 1) <-> tail call void @llvm.memcpy.element.unordered.atomic.p0i8.p0i8.i64(i8* align 1 %P, i8* align 1 %Q, i64 12, i32 1)
; CHECK: Both ModRef: Ptr: i8* %P <-> tail call void @llvm.memcpy.element.unordered.atomic.p0i8.p0i8.i64(i8* align 1 %P, i8* align 1 %Q, i64 12, i32 1)
; CHECK: Both ModRef: Ptr: i8* %Q <-> tail call void @llvm.memcpy.element.unordered.atomic.p0i8.p0i8.i64(i8* align 1 %P, i8* align 1 %Q, i64 12, i32 1)
; CHECK: Both ModRef: Ptr: i8* %P <-> tail call void @llvm.memcpy.element.unordered.atomic.p0i8.p0i8.i64(i8* align 1 %P, i8* align 1 %Q, i64 12, i32 1)
; CHECK: Both ModRef: Ptr: i8* %Q <-> tail call void @llvm.memcpy.element.unordered.atomic.p0i8.p0i8.i64(i8* align 1 %P, i8* align 1 %Q, i64 12, i32 1)
; CHECK: Both ModRef: tail call void @llvm.memcpy.element.unordered.atomic.p0i8.p0i8.i64(i8* align 1 %P, i8* align 1 %Q, i64 12, i32 1) <-> tail call void @llvm.memcpy.element.unordered.atomic.p0i8.p0i8.i64(i8* align 1 %P, i8* align 1 %Q, i64 12, i32 1)
; CHECK: Both ModRef: tail call void @llvm.memcpy.element.unordered.atomic.p0i8.p0i8.i64(i8* align 1 %P, i8* align 1 %Q, i64 12, i32 1) <-> tail call void @llvm.memcpy.element.unordered.atomic.p0i8.p0i8.i64(i8* align 1 %P, i8* align 1 %Q, i64 12, i32 1)
}
define void @test2a(i8* noalias %P, i8* noalias %Q) #3 {
@ -149,12 +149,12 @@ define void @test3(i8* %P, i8* %Q) #3 {
; CHECK-LABEL: Function: test3:
; CHECK: MayAlias: i8* %P, i8* %Q
; CHECK: Just Mod: Ptr: i8* %P <-> tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 8, i1 false)
; CHECK: Just Ref: Ptr: i8* %Q <-> tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 8, i1 false)
; CHECK: Just Mod: Ptr: i8* %P <-> tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
; CHECK: Just Ref: Ptr: i8* %Q <-> tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
; CHECK: Just Mod: tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 8, i1 false) <-> tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
; CHECK: Just Mod: tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false) <-> tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 8, i1 false)
; CHECK: Both ModRef: Ptr: i8* %P <-> tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 8, i1 false)
; CHECK: Both ModRef: Ptr: i8* %Q <-> tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 8, i1 false)
; CHECK: Both ModRef: Ptr: i8* %P <-> tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
; CHECK: Both ModRef: Ptr: i8* %Q <-> tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
; CHECK: Both ModRef: tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 8, i1 false) <-> tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
; CHECK: Both ModRef: tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false) <-> tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 8, i1 false)
}
define void @test3a(i8* noalias %P, i8* noalias %Q) #3 {
@ -199,14 +199,14 @@ define void @test5(i8* %P, i8* %Q, i8* %R) #3 {
; CHECK: MayAlias: i8* %P, i8* %Q
; CHECK: MayAlias: i8* %P, i8* %R
; CHECK: MayAlias: i8* %Q, i8* %R
; CHECK: Just Mod: Ptr: i8* %P <-> tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
; CHECK: Just Ref: Ptr: i8* %Q <-> tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
; CHECK: Both ModRef: Ptr: i8* %P <-> tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
; CHECK: Both ModRef: Ptr: i8* %Q <-> tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
; CHECK: Both ModRef: Ptr: i8* %R <-> tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
; CHECK: Just Mod: Ptr: i8* %P <-> tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %R, i64 12, i1 false)
; CHECK: Both ModRef: Ptr: i8* %P <-> tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %R, i64 12, i1 false)
; CHECK: Both ModRef: Ptr: i8* %Q <-> tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %R, i64 12, i1 false)
; CHECK: Just Ref: Ptr: i8* %R <-> tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %R, i64 12, i1 false)
; CHECK: Just Mod: tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false) <-> tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %R, i64 12, i1 false)
; CHECK: Just Mod: tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %R, i64 12, i1 false) <-> tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
; CHECK: Both ModRef: Ptr: i8* %R <-> tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %R, i64 12, i1 false)
; CHECK: Both ModRef: tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false) <-> tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %R, i64 12, i1 false)
; CHECK: Both ModRef: tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %R, i64 12, i1 false) <-> tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
}
define void @test5a(i8* noalias %P, i8* noalias %Q, i8* noalias %R) nounwind ssp {

4
test/Analysis/BasicAA/guards.ll
View File

@ -14,8 +14,8 @@ define void @test1(i8* %P, i8* %Q) {
; CHECK: Just Ref: Ptr: i8* %P <-> tail call void (i1, ...) @llvm.experimental.guard(i1 true) [ "deopt"() ]
; CHECK: Just Ref: Ptr: i8* %Q <-> tail call void (i1, ...) @llvm.experimental.guard(i1 true) [ "deopt"() ]
; CHECK: Just Mod: Ptr: i8* %P <-> tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
; CHECK: Just Ref: Ptr: i8* %Q <-> tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
; CHECK: Both ModRef: Ptr: i8* %P <-> tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
; CHECK: Both ModRef: Ptr: i8* %Q <-> tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
; CHECK: Just Ref: tail call void (i1, ...) @llvm.experimental.guard(i1 true) [ "deopt"() ] <-> tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
; CHECK: Just Mod: tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false) <-> tail call void (i1, ...) @llvm.experimental.guard(i1 true) [ "deopt"() ]
}

2
test/Analysis/MemorySSA/basicaa-memcpy.ll
View File

@ -6,7 +6,7 @@ define void @source_clobber(i8* %a, i8* %b) {
; CHECK-LABEL: @source_clobber(
; CHECK-NEXT: ; 1 = MemoryDef(liveOnEntry)
; CHECK-NEXT: call void @llvm.memcpy.p0i8.p0i8.i64(i8* %a, i8* %b, i64 128, i1 false)
; CHECK-NEXT: ; MemoryUse(liveOnEntry)
; CHECK-NEXT: ; MemoryUse(1) MayAlias
; CHECK-NEXT: [[X:%.*]] = load i8, i8* %b
; CHECK-NEXT: ret void
;

12
test/Transforms/DeadStoreElimination/MSSA/memset-and-memcpy.ll
View File

@ -68,13 +68,12 @@ define void @test17v(i8* %P, i8* %Q) nounwind ssp {
ret void
}
; According to the current LangRef, memcpy's source and destination cannot
; overlap, hence the first memcpy is dead.
;
; Previously this was not allowed (PR8728), also discussed in PR11763.
; See PR11763 - LLVM allows memcpy's source and destination to be equal (but not
; inequal and overlapping).
define void @test18(i8* %P, i8* %Q, i8* %R) nounwind ssp {
; CHECK-LABEL: @test18(
; CHECK-NEXT: tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* [[P:%.*]], i8* [[R:%.*]], i64 12, i1 false)
; CHECK-NEXT: tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* [[P:%.*]], i8* [[Q:%.*]], i64 12, i1 false)
; CHECK-NEXT: tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* [[P]], i8* [[R:%.*]], i64 12, i1 false)
; CHECK-NEXT: ret void
;
tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
@ -84,7 +83,8 @@ define void @test18(i8* %P, i8* %Q, i8* %R) nounwind ssp {
define void @test18_atomic(i8* %P, i8* %Q, i8* %R) nounwind ssp {
; CHECK-LABEL: @test18_atomic(
; CHECK-NEXT: tail call void @llvm.memcpy.element.unordered.atomic.p0i8.p0i8.i64(i8* align 1 [[P:%.*]], i8* align 1 [[R:%.*]], i64 12, i32 1)
; CHECK-NEXT: tail call void @llvm.memcpy.element.unordered.atomic.p0i8.p0i8.i64(i8* align 1 [[P:%.*]], i8* align 1 [[Q:%.*]], i64 12, i32 1)
; CHECK-NEXT: tail call void @llvm.memcpy.element.unordered.atomic.p0i8.p0i8.i64(i8* align 1 [[P]], i8* align 1 [[R:%.*]], i64 12, i32 1)
; CHECK-NEXT: ret void
;
tail call void @llvm.memcpy.element.unordered.atomic.p0i8.p0i8.i64(i8* align 1 %P, i8* align 1 %Q, i64 12, i32 1)

12
test/Transforms/DeadStoreElimination/MSSA/simple.ll
View File

@ -554,10 +554,12 @@ define void @test37_atomic(i8* %P, i8* %Q, i8* %R) {
ret void
}
; The memmove is dead, because memcpy arguments cannot overlap.
; See PR11763 - LLVM allows memcpy's source and destination to be equal (but not
; inequal and overlapping).
define void @test38(i8* %P, i8* %Q, i8* %R) {
; CHECK-LABEL: @test38(
; CHECK-NEXT: tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* [[P:%.*]], i8* [[R:%.*]], i64 12, i1 false)
; CHECK-NEXT: tail call void @llvm.memmove.p0i8.p0i8.i64(i8* [[P:%.*]], i8* [[Q:%.*]], i64 12, i1 false)
; CHECK-NEXT: tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* [[P]], i8* [[R:%.*]], i64 12, i1 false)
; CHECK-NEXT: ret void
;
@ -566,10 +568,12 @@ define void @test38(i8* %P, i8* %Q, i8* %R) {
ret void
}
; The memmove is dead, because memcpy arguments cannot overlap.
; See PR11763 - LLVM allows memcpy's source and destination to be equal (but not
; inequal and overlapping).
define void @test38_atomic(i8* %P, i8* %Q, i8* %R) {
; CHECK-LABEL: @test38_atomic(
; CHECK-NEXT: tail call void @llvm.memcpy.element.unordered.atomic.p0i8.p0i8.i64(i8* align 1 [[P:%.*]], i8* align 1 [[R:%.*]], i64 12, i32 1)
; CHECK-NEXT: tail call void @llvm.memmove.element.unordered.atomic.p0i8.p0i8.i64(i8* align 1 [[P:%.*]], i8* align 1 [[Q:%.*]], i64 12, i32 1)
; CHECK-NEXT: tail call void @llvm.memcpy.element.unordered.atomic.p0i8.p0i8.i64(i8* align 1 [[P]], i8* align 1 [[R:%.*]], i64 12, i32 1)
; CHECK-NEXT: ret void
;