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
50 lines
1.5 KiB
LLVM
50 lines
1.5 KiB
LLVM
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --function-signature
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; RUN: opt -S -O3 -o - %s | FileCheck %s
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; PR44154: LLVM c3b06d0c393e caused the body of @main to be replaced with
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; unreachable. Check that we perform the expected calls and optimizations.
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target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
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target triple = "x86_64-unknown-linux-gnu"
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define i32 @main(i32 %argc, i8** %argv) #0 {
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; CHECK-LABEL: define {{[^@]+}}@main
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; CHECK-SAME: (i32 [[ARGC:%.*]], i8** nocapture readnone [[ARGV:%.*]]) local_unnamed_addr #0
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; CHECK-NEXT: entry:
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; CHECK-NEXT: [[TMP0:%.*]] = icmp slt i32 [[ARGC]], 2
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; CHECK-NEXT: [[SPEC_SELECT:%.*]] = select i1 [[TMP0]], i32 0, i32 [[ARGC]]
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; CHECK-NEXT: ret i32 [[SPEC_SELECT]]
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;
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entry:
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%0 = getelementptr inbounds i8*, i8** %argv, i32 0
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%ptr = load i8*, i8** %0
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%1 = call i32 @compute(i8* %ptr, i32 %argc)
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%2 = icmp slt i32 %argc, 2
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br i1 %2, label %done, label %do_work
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do_work:
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%3 = icmp eq i8* %ptr, null
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br i1 %3, label %null, label %done
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null:
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call void @call_if_null(i8* %ptr)
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br label %done
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done:
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%retval = phi i32 [0, %entry], [%1, %do_work], [%1, %null]
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ret i32 %retval
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}
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define i32 @compute(i8* noundef nonnull %ptr, i32 %x) #1 {
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; CHECK-LABEL: define {{[^@]+}}@compute
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; CHECK-SAME: (i8* nocapture noundef nonnull readnone [[PTR:%.*]], i32 returned [[X:%.*]]) local_unnamed_addr #1
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; CHECK-NEXT: ret i32 [[X]]
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;
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ret i32 %x
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}
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declare void @call_if_null(i8* %ptr) #0
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attributes #0 = { nounwind }
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attributes #1 = { noinline nounwind readonly }
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