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[LICM] Only check for provenance captures (#141731)

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When performing scalar promotions, only consider provenance captures,
which may lead to non-thread-safe accesses. Address captures can be
ignored.
This commit is contained in:
Nikita Popov 2025-05-28 11:57:30 +02:00 committed by GitHub
parent 9262e37d8c
commit eea6969190
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GPG Key ID: B5690EEEBB952194
2 changed files with 55 additions and 2 deletions
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5
llvm/lib/Transforms/Scalar/LICM.cpp
View File

@ -1928,8 +1928,9 @@ bool isNotCapturedBeforeOrInLoop(const Value *V, const Loop *L,
// loop header, as the loop header is reachable from any instruction inside
// the loop.
// TODO: ReturnCaptures=true shouldn't be necessary here.
return !PointerMayBeCapturedBefore(V, /* ReturnCaptures */ true,
L->getHeader()->getTerminator(), DT);
return capturesNothing(PointerMayBeCapturedBefore(
V, /*ReturnCaptures=*/true, L->getHeader()->getTerminator(), DT,
/*IncludeI=*/false, CaptureComponents::Provenance));
}
/// Return true if we can prove that a caller cannot inspect the object if an

52
llvm/test/Transforms/LICM/promote-capture.ll
View File

@ -158,6 +158,58 @@ exit:
ret void
}
define void @test_captured_before_loop_address_only(i32 %len) {
; CHECK-LABEL: @test_captured_before_loop_address_only(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[COUNT:%.*]] = alloca i32, align 4
; CHECK-NEXT: store i32 0, ptr [[COUNT]], align 4
; CHECK-NEXT: call void @capture(ptr captures(address) [[COUNT]])
; CHECK-NEXT: [[COUNT_PROMOTED:%.*]] = load i32, ptr [[COUNT]], align 4
; CHECK-NEXT: br label [[LOOP:%.*]]
; CHECK: loop:
; CHECK-NEXT: [[C_INC2:%.*]] = phi i32 [ [[COUNT_PROMOTED]], [[ENTRY:%.*]] ], [ [[C_INC1:%.*]], [[LATCH:%.*]] ]
; CHECK-NEXT: [[I:%.*]] = phi i32 [ 0, [[ENTRY]] ], [ [[I_NEXT:%.*]], [[LATCH]] ]
; CHECK-NEXT: [[COND:%.*]] = call i1 @cond(i32 [[I]])
; CHECK-NEXT: br i1 [[COND]], label [[IF:%.*]], label [[LATCH]]
; CHECK: if:
; CHECK-NEXT: [[C_INC:%.*]] = add i32 [[C_INC2]], 1
; CHECK-NEXT: br label [[LATCH]]
; CHECK: latch:
; CHECK-NEXT: [[C_INC1]] = phi i32 [ [[C_INC]], [[IF]] ], [ [[C_INC2]], [[LOOP]] ]
; CHECK-NEXT: [[I_NEXT]] = add nuw i32 [[I]], 1
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i32 [[I_NEXT]], [[LEN:%.*]]
; CHECK-NEXT: br i1 [[CMP]], label [[EXIT:%.*]], label [[LOOP]]
; CHECK: exit:
; CHECK-NEXT: [[C_INC1_LCSSA:%.*]] = phi i32 [ [[C_INC1]], [[LATCH]] ]
; CHECK-NEXT: store i32 [[C_INC1_LCSSA]], ptr [[COUNT]], align 4
; CHECK-NEXT: ret void
;
entry:
%count = alloca i32
store i32 0, ptr %count
call void @capture(ptr captures(address) %count)
br label %loop
loop:
%i = phi i32 [ 0, %entry ], [ %i.next, %latch ]
%cond = call i1 @cond(i32 %i)
br i1 %cond, label %if, label %latch
if:
%c = load i32, ptr %count
%c.inc = add i32 %c, 1
store i32 %c.inc, ptr %count
br label %latch
latch:
%i.next = add nuw i32 %i, 1
%cmp = icmp eq i32 %i.next, %len
br i1 %cmp, label %exit, label %loop
exit:
ret void
}
; Should not get promoted, because the pointer is captured and may not
; be thread-local.
define void @test_captured_before_loop_byval(ptr byval(i32) align 4 %count, i32 %len) {