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[Attributor] Clarify volatile null pointer behavior (NFCI) (#193190)

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The comment was referring to volatile stores in particular, which
are specified as non-willreturn. However, allowing volatile accesses
on null (independently of null_pointer_is_valid) is a general
provision that is independent of the access kind.

The actual behavior was still correct, because volatile loads are
considered as writing inaccessible memory, so the mayWriteToMemory()
check was ultimately redundant.

Add a test to make sure volatile load is handled correctly.
This commit is contained in:
Nikita Popov
2026-04-21 12:54:25 +02:00
committed by GitHub
parent 47918c2c0a
commit af5fb3870a
2 changed files with 64 additions and 87 deletions
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4
llvm/lib/Transforms/IPO/AttributorAttributes.cpp
View File

@@ -2955,8 +2955,8 @@ struct AAUndefinedBehaviorImpl : public AAUndefinedBehavior {
const size_t NoUBPrevSize = AssumedNoUBInsts.size();
auto InspectMemAccessInstForUB = [&](Instruction &I) {
// Lang ref now states volatile store is not UB, let's skip them.
if (I.isVolatile() && I.mayWriteToMemory())
// Volatile accesses on null are not necessarily UB.
if (I.isVolatile())
return true;
// Skip instructions that are already saved.

147
llvm/test/Transforms/Attributor/undefined_behavior.ll
View File

@@ -20,6 +20,17 @@ define void @load_wholly_unreachable() {
ret void
}
define void @load_wholly_unreachable_volatile() {
; CHECK: Function Attrs: mustprogress nofree norecurse nounwind willreturn memory(none)
; CHECK-LABEL: define {{[^@]+}}@load_wholly_unreachable_volatile
; CHECK-SAME: () #[[ATTR1:[0-9]+]] {
; CHECK-NEXT: [[A:%.*]] = load volatile i32, ptr null, align 4
; CHECK-NEXT: ret void
;
%a = load volatile i32, ptr null
ret void
}
define void @loads_wholly_unreachable() {
; CHECK: Function Attrs: mustprogress nofree norecurse nosync nounwind willreturn memory(none)
; CHECK-LABEL: define {{[^@]+}}@loads_wholly_unreachable
@@ -55,7 +66,7 @@ e:
define void @load_null_pointer_is_defined() null_pointer_is_valid {
; CHECK: Function Attrs: mustprogress nofree norecurse nosync nounwind null_pointer_is_valid willreturn memory(none)
; CHECK-LABEL: define {{[^@]+}}@load_null_pointer_is_defined
; CHECK-SAME: () #[[ATTR1:[0-9]+]] {
; CHECK-SAME: () #[[ATTR2:[0-9]+]] {
; CHECK-NEXT: ret void
;
%a = load i32, ptr null
@@ -79,7 +90,7 @@ define void @load_null_propagated() {
;
; CGSCC: Function Attrs: mustprogress nofree nosync nounwind willreturn memory(none)
; CGSCC-LABEL: define {{[^@]+}}@load_null_propagated
; CGSCC-SAME: () #[[ATTR2:[0-9]+]] {
; CGSCC-SAME: () #[[ATTR3:[0-9]+]] {
; CGSCC-NEXT: ret void
;
%ptr = call ptr @ret_null()
@@ -100,17 +111,11 @@ define void @store_wholly_unreachable() {
}
define void @store_wholly_unreachable_volatile() {
; TUNIT: Function Attrs: mustprogress nofree norecurse nounwind willreturn memory(none)
; TUNIT-LABEL: define {{[^@]+}}@store_wholly_unreachable_volatile
; TUNIT-SAME: () #[[ATTR2:[0-9]+]] {
; TUNIT-NEXT: store volatile i32 5, ptr null, align 4
; TUNIT-NEXT: ret void
;
; CGSCC: Function Attrs: mustprogress nofree norecurse nounwind willreturn memory(none)
; CGSCC-LABEL: define {{[^@]+}}@store_wholly_unreachable_volatile
; CGSCC-SAME: () #[[ATTR3:[0-9]+]] {
; CGSCC-NEXT: store volatile i32 5, ptr null, align 4
; CGSCC-NEXT: ret void
; CHECK: Function Attrs: mustprogress nofree norecurse nounwind willreturn memory(none)
; CHECK-LABEL: define {{[^@]+}}@store_wholly_unreachable_volatile
; CHECK-SAME: () #[[ATTR1]] {
; CHECK-NEXT: store volatile i32 5, ptr null, align 4
; CHECK-NEXT: ret void
;
store volatile i32 5, ptr null
ret void
@@ -174,38 +179,24 @@ define void @store_null_propagated() {
; -- AtomicRMW tests --
define void @atomicrmw_wholly_unreachable() {
; TUNIT: Function Attrs: mustprogress nofree norecurse nounwind willreturn memory(none)
; TUNIT-LABEL: define {{[^@]+}}@atomicrmw_wholly_unreachable
; TUNIT-SAME: () #[[ATTR2]] {
; TUNIT-NEXT: unreachable
;
; CGSCC: Function Attrs: mustprogress nofree norecurse nounwind willreturn memory(none)
; CGSCC-LABEL: define {{[^@]+}}@atomicrmw_wholly_unreachable
; CGSCC-SAME: () #[[ATTR3]] {
; CGSCC-NEXT: unreachable
; CHECK: Function Attrs: mustprogress nofree norecurse nounwind willreturn memory(none)
; CHECK-LABEL: define {{[^@]+}}@atomicrmw_wholly_unreachable
; CHECK-SAME: () #[[ATTR1]] {
; CHECK-NEXT: unreachable
;
%a = atomicrmw add ptr null, i32 1 acquire
ret void
}
define void @atomicrmw_single_bb_unreachable(i1 %cond) {
; TUNIT: Function Attrs: mustprogress nofree norecurse nounwind willreturn memory(none)
; TUNIT-LABEL: define {{[^@]+}}@atomicrmw_single_bb_unreachable
; TUNIT-SAME: (i1 noundef [[COND:%.*]]) #[[ATTR2]] {
; TUNIT-NEXT: br i1 [[COND]], label [[T:%.*]], label [[E:%.*]]
; TUNIT: t:
; TUNIT-NEXT: unreachable
; TUNIT: e:
; TUNIT-NEXT: ret void
;
; CGSCC: Function Attrs: mustprogress nofree norecurse nounwind willreturn memory(none)
; CGSCC-LABEL: define {{[^@]+}}@atomicrmw_single_bb_unreachable
; CGSCC-SAME: (i1 noundef [[COND:%.*]]) #[[ATTR3]] {
; CGSCC-NEXT: br i1 [[COND]], label [[T:%.*]], label [[E:%.*]]
; CGSCC: t:
; CGSCC-NEXT: unreachable
; CGSCC: e:
; CGSCC-NEXT: ret void
; CHECK: Function Attrs: mustprogress nofree norecurse nounwind willreturn memory(none)
; CHECK-LABEL: define {{[^@]+}}@atomicrmw_single_bb_unreachable
; CHECK-SAME: (i1 noundef [[COND:%.*]]) #[[ATTR1]] {
; CHECK-NEXT: br i1 [[COND]], label [[T:%.*]], label [[E:%.*]]
; CHECK: t:
; CHECK-NEXT: unreachable
; CHECK: e:
; CHECK-NEXT: ret void
;
br i1 %cond, label %t, label %e
t:
@@ -238,7 +229,7 @@ define void @atomicrmw_null_propagated() {
;
; TUNIT: Function Attrs: mustprogress nofree norecurse nounwind willreturn memory(none)
; TUNIT-LABEL: define {{[^@]+}}@atomicrmw_null_propagated
; TUNIT-SAME: () #[[ATTR2]] {
; TUNIT-SAME: () #[[ATTR1]] {
; TUNIT-NEXT: unreachable
;
; CGSCC: Function Attrs: mustprogress nofree nounwind willreturn
@@ -256,38 +247,24 @@ define void @atomicrmw_null_propagated() {
; -- AtomicCmpXchg tests --
define void @atomiccmpxchg_wholly_unreachable() {
; TUNIT: Function Attrs: mustprogress nofree norecurse nounwind willreturn memory(none)
; TUNIT-LABEL: define {{[^@]+}}@atomiccmpxchg_wholly_unreachable
; TUNIT-SAME: () #[[ATTR2]] {
; TUNIT-NEXT: unreachable
;
; CGSCC: Function Attrs: mustprogress nofree norecurse nounwind willreturn memory(none)
; CGSCC-LABEL: define {{[^@]+}}@atomiccmpxchg_wholly_unreachable
; CGSCC-SAME: () #[[ATTR3]] {
; CGSCC-NEXT: unreachable
; CHECK: Function Attrs: mustprogress nofree norecurse nounwind willreturn memory(none)
; CHECK-LABEL: define {{[^@]+}}@atomiccmpxchg_wholly_unreachable
; CHECK-SAME: () #[[ATTR1]] {
; CHECK-NEXT: unreachable
;
%a = cmpxchg ptr null, i32 2, i32 3 acq_rel monotonic
ret void
}
define void @atomiccmpxchg_single_bb_unreachable(i1 %cond) {
; TUNIT: Function Attrs: mustprogress nofree norecurse nounwind willreturn memory(none)
; TUNIT-LABEL: define {{[^@]+}}@atomiccmpxchg_single_bb_unreachable
; TUNIT-SAME: (i1 noundef [[COND:%.*]]) #[[ATTR2]] {
; TUNIT-NEXT: br i1 [[COND]], label [[T:%.*]], label [[E:%.*]]
; TUNIT: t:
; TUNIT-NEXT: unreachable
; TUNIT: e:
; TUNIT-NEXT: ret void
;
; CGSCC: Function Attrs: mustprogress nofree norecurse nounwind willreturn memory(none)
; CGSCC-LABEL: define {{[^@]+}}@atomiccmpxchg_single_bb_unreachable
; CGSCC-SAME: (i1 noundef [[COND:%.*]]) #[[ATTR3]] {
; CGSCC-NEXT: br i1 [[COND]], label [[T:%.*]], label [[E:%.*]]
; CGSCC: t:
; CGSCC-NEXT: unreachable
; CGSCC: e:
; CGSCC-NEXT: ret void
; CHECK: Function Attrs: mustprogress nofree norecurse nounwind willreturn memory(none)
; CHECK-LABEL: define {{[^@]+}}@atomiccmpxchg_single_bb_unreachable
; CHECK-SAME: (i1 noundef [[COND:%.*]]) #[[ATTR1]] {
; CHECK-NEXT: br i1 [[COND]], label [[T:%.*]], label [[E:%.*]]
; CHECK: t:
; CHECK-NEXT: unreachable
; CHECK: e:
; CHECK-NEXT: ret void
;
br i1 %cond, label %t, label %e
t:
@@ -320,7 +297,7 @@ define void @atomiccmpxchg_null_propagated() {
;
; TUNIT: Function Attrs: mustprogress nofree norecurse nounwind willreturn memory(none)
; TUNIT-LABEL: define {{[^@]+}}@atomiccmpxchg_null_propagated
; TUNIT-SAME: () #[[ATTR2]] {
; TUNIT-SAME: () #[[ATTR1]] {
; TUNIT-NEXT: unreachable
;
; CGSCC: Function Attrs: mustprogress nofree nounwind willreturn
@@ -414,7 +391,7 @@ define void @cond_br_on_undef_interproc() {
;
; CGSCC: Function Attrs: mustprogress nofree nosync nounwind willreturn memory(none)
; CGSCC-LABEL: define {{[^@]+}}@cond_br_on_undef_interproc
; CGSCC-SAME: () #[[ATTR2]] {
; CGSCC-SAME: () #[[ATTR3]] {
; CGSCC-NEXT: [[COND:%.*]] = call i1 @ret_undef() #[[ATTR10]]
; CGSCC-NEXT: br i1 [[COND]], label [[T:%.*]], label [[E:%.*]]
; CGSCC: t:
@@ -460,7 +437,7 @@ define void @cond_br_on_undef_interproc2() {
;
; CGSCC: Function Attrs: mustprogress nofree nosync nounwind willreturn memory(none)
; CGSCC-LABEL: define {{[^@]+}}@cond_br_on_undef_interproc2
; CGSCC-SAME: () #[[ATTR2]] {
; CGSCC-SAME: () #[[ATTR3]] {
; CGSCC-NEXT: [[COND:%.*]] = call i1 @ret_undef2() #[[ATTR10]]
; CGSCC-NEXT: br i1 [[COND]], label [[T:%.*]], label [[E:%.*]]
; CGSCC: t:
@@ -570,7 +547,7 @@ define i32 @foo() {
;
; CGSCC: Function Attrs: mustprogress nofree nosync nounwind willreturn memory(none)
; CGSCC-LABEL: define {{[^@]+}}@foo
; CGSCC-SAME: () #[[ATTR2]] {
; CGSCC-SAME: () #[[ATTR3]] {
; CGSCC-NEXT: [[X:%.*]] = call noundef i32 @callee() #[[ATTR10]]
; CGSCC-NEXT: ret i32 [[X]]
;
@@ -707,7 +684,7 @@ define void @arg_nonnull_violation1_1() {
;
; CGSCC: Function Attrs: mustprogress nofree nosync nounwind willreturn memory(none)
; CGSCC-LABEL: define {{[^@]+}}@arg_nonnull_violation1_1
; CGSCC-SAME: () #[[ATTR2]] {
; CGSCC-SAME: () #[[ATTR3]] {
; CGSCC-NEXT: unreachable
;
call void @arg_nonnull_1(ptr null)
@@ -722,7 +699,7 @@ define void @arg_nonnull_violation1_2() {
;
; CGSCC: Function Attrs: mustprogress nofree nosync nounwind willreturn memory(none)
; CGSCC-LABEL: define {{[^@]+}}@arg_nonnull_violation1_2
; CGSCC-SAME: () #[[ATTR2]] {
; CGSCC-SAME: () #[[ATTR3]] {
; CGSCC-NEXT: unreachable
;
call void @arg_nonnull_1_noundef_1(ptr null)
@@ -738,7 +715,7 @@ define void @arg_nonnull_violation2_1(i1 %c) {
;
; CGSCC: Function Attrs: mustprogress nofree nosync nounwind willreturn memory(none)
; CGSCC-LABEL: define {{[^@]+}}@arg_nonnull_violation2_1
; CGSCC-SAME: (i1 [[C:%.*]]) #[[ATTR2]] {
; CGSCC-SAME: (i1 [[C:%.*]]) #[[ATTR3]] {
; CGSCC-NEXT: unreachable
;
%mustnull = select i1 %c, ptr null, ptr null
@@ -754,7 +731,7 @@ define void @arg_nonnull_violation2_2(i1 %c) {
;
; CGSCC: Function Attrs: mustprogress nofree nosync nounwind willreturn memory(none)
; CGSCC-LABEL: define {{[^@]+}}@arg_nonnull_violation2_2
; CGSCC-SAME: (i1 [[C:%.*]]) #[[ATTR2]] {
; CGSCC-SAME: (i1 [[C:%.*]]) #[[ATTR3]] {
; CGSCC-NEXT: unreachable
;
%mustnull = select i1 %c, ptr null, ptr null
@@ -780,7 +757,7 @@ define void @arg_nonnull_violation3_1(i1 %c) {
;
; CGSCC: Function Attrs: mustprogress nofree nosync nounwind willreturn memory(none)
; CGSCC-LABEL: define {{[^@]+}}@arg_nonnull_violation3_1
; CGSCC-SAME: (i1 noundef [[C:%.*]]) #[[ATTR2]] {
; CGSCC-SAME: (i1 noundef [[C:%.*]]) #[[ATTR3]] {
; CGSCC-NEXT: [[PTR:%.*]] = alloca i32, align 4
; CGSCC-NEXT: br i1 [[C]], label [[T:%.*]], label [[F:%.*]]
; CGSCC: t:
@@ -827,7 +804,7 @@ define void @arg_nonnull_violation3_2(i1 %c) {
;
; CGSCC: Function Attrs: mustprogress nofree nosync nounwind willreturn memory(none)
; CGSCC-LABEL: define {{[^@]+}}@arg_nonnull_violation3_2
; CGSCC-SAME: (i1 noundef [[C:%.*]]) #[[ATTR2]] {
; CGSCC-SAME: (i1 noundef [[C:%.*]]) #[[ATTR3]] {
; CGSCC-NEXT: [[PTR:%.*]] = alloca i32, align 4
; CGSCC-NEXT: br i1 [[C]], label [[T:%.*]], label [[F:%.*]]
; CGSCC: t:
@@ -987,7 +964,7 @@ define i32 @violate_noundef_nonpointer() {
;
; CGSCC: Function Attrs: mustprogress nofree nosync nounwind willreturn memory(none)
; CGSCC-LABEL: define {{[^@]+}}@violate_noundef_nonpointer
; CGSCC-SAME: () #[[ATTR2]] {
; CGSCC-SAME: () #[[ATTR3]] {
; CGSCC-NEXT: unreachable
;
%ret = call i32 @argument_noundef1(i32 undef)
@@ -1011,7 +988,7 @@ define ptr @violate_noundef_pointer() {
;
; CGSCC: Function Attrs: mustprogress nofree nosync nounwind willreturn memory(none)
; CGSCC-LABEL: define {{[^@]+}}@violate_noundef_pointer
; CGSCC-SAME: () #[[ATTR2]] {
; CGSCC-SAME: () #[[ATTR3]] {
; CGSCC-NEXT: ret ptr undef
;
%ret = call ptr @argument_noundef2(ptr undef)
@@ -1021,7 +998,7 @@ define ptr @violate_noundef_pointer() {
define internal noundef i32 @assumed_undef_is_ok(i1 %c, i32 %arg) {
; CGSCC: Function Attrs: mustprogress nofree nosync nounwind willreturn memory(none)
; CGSCC-LABEL: define {{[^@]+}}@assumed_undef_is_ok
; CGSCC-SAME: (i1 noundef [[C:%.*]]) #[[ATTR2]] {
; CGSCC-SAME: (i1 noundef [[C:%.*]]) #[[ATTR3]] {
; CGSCC-NEXT: br i1 [[C]], label [[REC:%.*]], label [[RET:%.*]]
; CGSCC: rec:
; CGSCC-NEXT: br label [[RET]]
@@ -1048,7 +1025,7 @@ define noundef i32 @assumed_undef_is_ok_caller(i1 %c) {
;
; CGSCC: Function Attrs: mustprogress nofree nosync nounwind willreturn memory(none)
; CGSCC-LABEL: define {{[^@]+}}@assumed_undef_is_ok_caller
; CGSCC-SAME: (i1 noundef [[C:%.*]]) #[[ATTR2]] {
; CGSCC-SAME: (i1 noundef [[C:%.*]]) #[[ATTR3]] {
; CGSCC-NEXT: [[CALL:%.*]] = call i32 @assumed_undef_is_ok(i1 noundef [[C]]) #[[ATTR10]]
; CGSCC-NEXT: ret i32 [[CALL]]
;
@@ -1058,8 +1035,8 @@ define noundef i32 @assumed_undef_is_ok_caller(i1 %c) {
;.
; TUNIT: attributes #[[ATTR0]] = { mustprogress nofree norecurse nosync nounwind willreturn memory(none) }
; TUNIT: attributes #[[ATTR1]] = { mustprogress nofree norecurse nosync nounwind null_pointer_is_valid willreturn memory(none) }
; TUNIT: attributes #[[ATTR2]] = { mustprogress nofree norecurse nounwind willreturn memory(none) }
; TUNIT: attributes #[[ATTR1]] = { mustprogress nofree norecurse nounwind willreturn memory(none) }
; TUNIT: attributes #[[ATTR2]] = { mustprogress nofree norecurse nosync nounwind null_pointer_is_valid willreturn memory(none) }
; TUNIT: attributes #[[ATTR3]] = { mustprogress nofree norecurse nosync nounwind null_pointer_is_valid willreturn memory(write) }
; TUNIT: attributes #[[ATTR4]] = { mustprogress nofree norecurse nounwind null_pointer_is_valid willreturn }
; TUNIT: attributes #[[ATTR5]] = { mustprogress nofree norecurse noreturn nosync nounwind willreturn memory(none) }
@@ -1067,9 +1044,9 @@ define noundef i32 @assumed_undef_is_ok_caller(i1 %c) {
; TUNIT: attributes #[[ATTR7]] = { nofree nosync nounwind willreturn memory(write) }
;.
; CGSCC: attributes #[[ATTR0]] = { mustprogress nofree norecurse nosync nounwind willreturn memory(none) }
; CGSCC: attributes #[[ATTR1]] = { mustprogress nofree norecurse nosync nounwind null_pointer_is_valid willreturn memory(none) }
; CGSCC: attributes #[[ATTR2]] = { mustprogress nofree nosync nounwind willreturn memory(none) }
; CGSCC: attributes #[[ATTR3]] = { mustprogress nofree norecurse nounwind willreturn memory(none) }
; CGSCC: attributes #[[ATTR1]] = { mustprogress nofree norecurse nounwind willreturn memory(none) }
; CGSCC: attributes #[[ATTR2]] = { mustprogress nofree norecurse nosync nounwind null_pointer_is_valid willreturn memory(none) }
; CGSCC: attributes #[[ATTR3]] = { mustprogress nofree nosync nounwind willreturn memory(none) }
; CGSCC: attributes #[[ATTR4]] = { mustprogress nofree norecurse nosync nounwind null_pointer_is_valid willreturn memory(write) }
; CGSCC: attributes #[[ATTR5]] = { mustprogress nofree nosync nounwind willreturn memory(write) }
; CGSCC: attributes #[[ATTR6]] = { mustprogress nofree norecurse nounwind null_pointer_is_valid willreturn }