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c64e878f84
Summary:
This patch is crucial for proving equality laundered/stripped
pointers. eg:
bool foo(A *a) {
return a == std::launder(a);
}
Clang with -fstrict-vtable-pointers will emit something like:
define dso_local zeroext i1 @_Z3fooP1A(%struct.A* %a) {
entry:
%c = bitcast %struct.A* %a to i8*
%call = tail call i8* @llvm.launder.invariant.group.p0i8(i8* %c)
%0 = bitcast %struct.A* %a to i8*
%1 = tail call i8* @llvm.strip.invariant.group.p0i8(i8* %0)
%2 = tail call i8* @llvm.strip.invariant.group.p0i8(i8* %call)
%cmp = icmp eq i8* %1, %2
ret i1 %cmp
}
and because %2 can be replaced with @llvm.strip.invariant.group(%0)
and that %2 and %1 will produce the same value (because strip is readnone)
we can replace compare with true.
Reviewers: rsmith, hfinkel, majnemer, amharc, kuhar
Subscribers: llvm-commits, hiraditya
Differential Revision: https://reviews.llvm.org/D47423
llvm-svn: 336963
35 lines
998 B
LLVM
35 lines
998 B
LLVM
; RUN: opt -S -instsimplify -instcombine < %s | FileCheck %s
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; CHECK-LABEL: define void @checkNonnullLaunder()
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define void @checkNonnullLaunder() {
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; CHECK: %[[p:.*]] = call i8* @llvm.launder.invariant.group.p0i8(i8* nonnull %0)
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; CHECK: call void @use(i8* nonnull %[[p]])
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entry:
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%0 = alloca i8, align 8
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%p = call i8* @llvm.launder.invariant.group.p0i8(i8* %0)
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%p2 = call i8* @llvm.launder.invariant.group.p0i8(i8* %p)
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call void @use(i8* %p2)
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ret void
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}
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; CHECK-LABEL: define void @checkNonnullStrip()
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define void @checkNonnullStrip() {
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; CHECK: %[[p:.*]] = call i8* @llvm.strip.invariant.group.p0i8(i8* nonnull %0)
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; CHECK: call void @use(i8* nonnull %[[p]])
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entry:
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%0 = alloca i8, align 8
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%p = call i8* @llvm.strip.invariant.group.p0i8(i8* %0)
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%p2 = call i8* @llvm.strip.invariant.group.p0i8(i8* %p)
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call void @use(i8* %p2)
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ret void
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}
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declare i8* @llvm.launder.invariant.group.p0i8(i8*)
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declare i8* @llvm.strip.invariant.group.p0i8(i8*)
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declare void @use(i8*)
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