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Fix handling of allocation functions without allocsize attribute - #1238 #1252

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Fix handling of allocation functions without allocsize attribute - #1238 #1252

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c1908c5
Handle alloc/realloc calls without AllocSize
IamYJLee Jan 5, 2026
2e0640f
Improve AllocSize handling following code review feedback
IamYJLee Jan 7, 2026
77db5dd
Add read-only attribute to addFnCall
IamYJLee Jan 21, 2026
b425d12
Merge branch 'AliveToolkit:master' into fix-1238
IamYJLee Jan 28, 2026
183a78f
Use addFnCall to mark allocator calls with inaccessible memory side e…
IamYJLee Feb 2, 2026
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1 change: 1 addition & 0 deletions ir/attrs.h
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Original file line number Diff line number Diff line change
Expand Up @@ -158,6 +158,7 @@ class FnAttrs final {
void add(AllocKind k) { allockind |= (uint8_t)k; }
bool has(AllocKind k) const { return allockind & (uint8_t)k; }
bool isAlloc() const { return allockind != 0 || has(AllocSize); }
bool isAllocWithoutSize() const { return allockind != 0 && !has(AllocSize); }

void inferImpliedAttributes();

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18 changes: 17 additions & 1 deletion ir/instr.cpp
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Expand Up @@ -2684,7 +2684,23 @@ StateValue FnCall::toSMT(State &s) const {
if (attrs.has(AllocKind::Alloc) ||
attrs.has(AllocKind::Realloc) ||
attrs.has(FnAttrs::AllocSize)) {
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auto [size, np_size] = attrs.computeAllocSize(s, args);

smt::expr size;
smt::expr np_size;

if (!attrs.has(FnAttrs::AllocSize)) {
static IntType sizet_type(string("size_t"), config::max_sizet_bits);
auto result = s.addFnCall(std::move(fnName_mangled).str(), std::move(inputs),
std::move(ptr_inputs), sizet_type, StateValue{},
nullptr, std::vector<StateValue>{}, attrs, indirect_hash);

@nunoplopes nunoplopes Jan 7, 2026

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I think we need to adjust the attrs here so the call is read-only.

@IamYJLee IamYJLee Jan 8, 2026 •
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FnAttrs readonly_attrs = attrs;
readonly_attrs.mem.setCanOnlyRead();
auto result = s.addFnCall(std::move(fnName_mangled).str(), std::move(inputs),
      std::move(ptr_inputs), sizet_type, StateValue{},
      nullptr, std::vector<StateValue>{}, readonly_attrs, indirect_hash);

I attempted the change as above, yet the error ERROR: Source and target don't have the same return domain persists.
I think this may be due to the existence of counterexamples in which the myalloc function fails to return.
Would it make sense to add the willreturn attribute to explicitly state that the user-defined allocator always returns (possibly with any value)?

@IamYJLee IamYJLee Jan 8, 2026 •
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The semantics of this behavior are not explicitly specified in the LLVM Language Reference.

@nunoplopes nunoplopes Jan 12, 2026

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Uhm, that's a good point about willreturn. LLVM currently removes calls to custom allocators, though.
Would you mind opening either a discussion on discourse or a bug report to clarify the assumptions on custom allocators, (and CC me) please? Thanks!

size = std::move(result.value);
np_size = std::move(result.non_poison);
} else {
auto result = attrs.computeAllocSize(s, args);
size = std::move(result.first);
np_size = std::move(result.second);
}

expr nonnull = attrs.isNonNull() ? expr(true)
: expr::mkBoolVar("malloc_never_fails");
// FIXME: alloc-family below
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14 changes: 14 additions & 0 deletions tests/alive-tv/attrs/noallocsize-fn.srctgt.ll
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@@ -0,0 +1,14 @@
; ERROR: Source and target don't have the same return domain

@nunoplopes nunoplopes Jan 7, 2026

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This is the wrong output. A call into an allocator can be removed.


define i64 @src() {
%stack = call ptr @myalloc()
%sz = call i64 @llvm.objectsize.i64.p0(ptr %stack, i1 false, i1 false, i1 false)
ret i64 %sz
}

define i64 @tgt() {
ret i64 -1
}

declare ptr @myalloc() allockind("alloc")
declare i64 @llvm.objectsize.i64.p0(ptr, i1, i1, i1)
3 changes: 3 additions & 0 deletions tools/transform.cpp
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Expand Up @@ -1163,6 +1163,9 @@ static void calculateAndInitConstants(Transform &t) {
inaccessiblememonly_fns.emplace(call->getName()).second)
++num_inaccessiblememonly_fns;
}
if(attrs.isAllocWithoutSize()) {

@nunoplopes nunoplopes Jan 7, 2026

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missing space here before (

has_write_fncall |= attrs.mem.canWriteSomething();

@nunoplopes nunoplopes Jan 7, 2026

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I don't think we want the call to get the object size to write anything.

@IamYJLee IamYJLee Jan 8, 2026 •
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I will adjust the arguments to addFnCall to make the call read-only, which enables the removal of this code.

}
if (call->isIndirect()) {
has_indirect_fncalls = true;
num_inaccessiblememonly_fns += is_src;
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