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[Attributes] Remove nonnull from UB-implying attributes

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From LangRef:

> if the parameter or return pointer is null, poison value is
> returned or passed instead. The nonnull attribute should be
> combined with the noundef attribute to ensure a pointer is not
> null or otherwise the behavior is undefined.

Dropping noundef is sufficient to prevent UB. Including nonnull
in this method just muddies the semantics.
This commit is contained in:
Nikita Popov 2021-07-25 18:04:50 +02:00
parent 4c407a3b35
commit adc5107b73
3 changed files with 7 additions and 8 deletions
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1
lib/IR/Attributes.cpp
View File

@ -1340,7 +1340,6 @@ AttributeList::removeParamUndefImplyingAttributes(LLVMContext &C,
unsigned ArgNo) const {
AttrBuilder B;
B.addAttribute(Attribute::NoUndef);
B.addAttribute(Attribute::NonNull);
B.addDereferenceableAttr(1);
B.addDereferenceableOrNullAttr(1);
return removeParamAttributes(C, ArgNo, B);

10
test/Transforms/DeadArgElim/NoundefAttrs.ll
View File

@ -1,10 +1,10 @@
; RUN: opt -deadargelim -S < %s | FileCheck %s
; If caller is changed to pass in undef, noundef and related attributes
; should be deleted.
; If caller is changed to pass in undef, noundef, dereferenceable and other
; attributes that imply immediate undefined behavior should be delete.
; Other attributes like nonnull, which only imply poison, can be safely kept.
; CHECK: define i64 @bar(i64* %0, i64 %1)
; CHECK: define i64 @bar(i64* nonnull %0, i64 %1)
define i64 @bar(i64* nonnull dereferenceable(8) %0, i64 %1) {
entry:
%2 = add i64 %1, 8
@ -12,7 +12,7 @@ entry:
}
define i64 @foo(i64* %p, i64 %v) {
; CHECK: %retval = call i64 @bar(i64* undef, i64 %v)
; CHECK: %retval = call i64 @bar(i64* nonnull undef, i64 %v)
%retval = call i64 @bar(i64* nonnull dereferenceable(8) %p, i64 %v)
ret i64 %retval
}

4
test/Transforms/InstCombine/unused-nonnull.ll
View File

@ -9,7 +9,7 @@ target triple = "x86_64-unknown-linux-gnu"
define i32 @main(i32 %argc, i8** %argv) #0 {
; CHECK-LABEL: define {{[^@]+}}@main
; CHECK-SAME: (i32 [[ARGC:%.*]], i8** nocapture readnone [[ARGV:%.*]]) local_unnamed_addr #0
; CHECK-SAME: (i32 [[ARGC:%.*]], i8** nocapture readnone [[ARGV:%.*]]) local_unnamed_addr #[[ATTR0:[0-9]+]] {
; CHECK-NEXT: entry:
; CHECK-NEXT: [[TMP0:%.*]] = icmp slt i32 [[ARGC]], 2
; CHECK-NEXT: [[SPEC_SELECT:%.*]] = select i1 [[TMP0]], i32 0, i32 [[ARGC]]
@ -37,7 +37,7 @@ done:
define i32 @compute(i8* noundef nonnull %ptr, i32 %x) #1 {
; CHECK-LABEL: define {{[^@]+}}@compute
; CHECK-SAME: (i8* nocapture readnone [[PTR:%.*]], i32 returned [[X:%.*]]) local_unnamed_addr #1
; CHECK-SAME: (i8* nocapture nonnull readnone [[PTR:%.*]], i32 returned [[X:%.*]]) local_unnamed_addr #[[ATTR1:[0-9]+]] {
; CHECK-NEXT: ret i32 [[X]]
;
ret i32 %x