4479c0c2c0
Currently LLVM is relying on ValueTracking's `isKnownNonZero` to attach `nonnull`, which can return true when the value is poison.
To make the semantics of `nonnull` consistent with the behavior of `isKnownNonZero`, this makes the semantics of `nonnull` to accept poison, and return poison if the input pointer isn't null.
This makes many transformations like below legal:
```
%p = gep inbounds %x, 1 ; % p is non-null pointer or poison
call void @f(%p) ; instcombine converts this to call void @f(nonnull %p)
```
Instead, this semantics makes propagation of `nonnull` to caller illegal.
The reason is that, passing poison to `nonnull` does not immediately raise UB anymore, so such program is still well defined, if the callee does not use the argument.
Having `noundef` attribute there re-allows this.
```
define void @f(i8* %p) { ; functionattr cannot mark %p nonnull here anymore
call void @g(i8* nonnull %p) ; .. because @g never raises UB if it never uses %p.
ret void
}
```
Another attribute that needs to be updated is `align`. This patch updates the semantics of align to accept poison as well.
Reviewed By: jdoerfert
Differential Revision: https://reviews.llvm.org/D90529
64 lines
1.9 KiB
LLVM
64 lines
1.9 KiB
LLVM
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
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; RUN: opt < %s -instcombine -S | FileCheck %s
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; InstCombine should mark null-checked argument as nonnull at callsite
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declare void @dummy(i32*, i32)
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define void @test(i32* %a, i32 %b) {
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; CHECK-LABEL: @test(
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; CHECK-NEXT: entry:
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; CHECK-NEXT: [[COND1:%.*]] = icmp eq i32* [[A:%.*]], null
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; CHECK-NEXT: br i1 [[COND1]], label [[DEAD:%.*]], label [[NOT_NULL:%.*]]
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; CHECK: not_null:
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; CHECK-NEXT: [[COND2:%.*]] = icmp eq i32 [[B:%.*]], 0
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; CHECK-NEXT: br i1 [[COND2]], label [[DEAD]], label [[NOT_ZERO:%.*]]
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; CHECK: not_zero:
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; CHECK-NEXT: call void @dummy(i32* nonnull [[A]], i32 [[B]])
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; CHECK-NEXT: ret void
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; CHECK: dead:
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; CHECK-NEXT: unreachable
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;
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entry:
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%cond1 = icmp eq i32* %a, null
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br i1 %cond1, label %dead, label %not_null
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not_null:
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%cond2 = icmp eq i32 %b, 0
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br i1 %cond2, label %dead, label %not_zero
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not_zero:
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call void @dummy(i32* %a, i32 %b)
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ret void
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dead:
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unreachable
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}
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; The nonnull attribute in the 'bar' declaration is
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; propagated to the parameters of the 'baz' callsite.
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declare void @bar(i8*, i8* nonnull noundef)
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declare void @bar_without_noundef(i8*, i8* nonnull)
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declare void @baz(i8*, i8*)
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define void @deduce_nonnull_from_another_call(i8* %a, i8* %b) {
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; CHECK-LABEL: @deduce_nonnull_from_another_call(
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; CHECK-NEXT: call void @bar(i8* [[A:%.*]], i8* [[B:%.*]])
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; CHECK-NEXT: call void @baz(i8* nonnull [[B]], i8* nonnull [[B]])
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; CHECK-NEXT: ret void
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;
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call void @bar(i8* %a, i8* %b)
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call void @baz(i8* %b, i8* %b)
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ret void
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}
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define void @deduce_nonnull_from_another_call2(i8* %a, i8* %b) {
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; CHECK-LABEL: @deduce_nonnull_from_another_call2(
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; CHECK-NEXT: call void @bar_without_noundef(i8* [[A:%.*]], i8* [[B:%.*]])
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; CHECK-NEXT: call void @baz(i8* [[B]], i8* [[B]])
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; CHECK-NEXT: ret void
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;
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call void @bar_without_noundef(i8* %a, i8* %b)
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call void @baz(i8* %b, i8* %b)
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ret void
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}
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