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[inferattrs] Don't infer lib func attributes for nobuiltin functions

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If we have a nobuiltin function, we can't assume we know anything about the implementation.

I noticed this when tracing through a log from an in the wild miscompile (https://github.com/emscripten-core/emscripten/issues/9443) triggered after 8666463.  We were incorrectly assuming that a custom allocator could not free.  (It's not clear yet this is the only problem in said issue.)

I also noticed something similiar mentioned in the commit message of ab243e when scrolling back through history.  Through, from what I can tell, that commit fixed symptom not root cause.

The interface we have for library function detection is extremely error prone, but given the interaction between ``nobuiltin`` decls and ``builtin`` callsites, it's really hard to imagine something much cleaner.  I may iterate on that, but it'll be invasive enough I didn't want to hold an obvious functional fix on it.
This commit is contained in:
Philip Reames 2021-04-16 15:28:15 -07:00
parent af14859209
commit e84c42802f
2 changed files with 7 additions and 1 deletions
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3
lib/Transforms/IPO/InferFunctionAttrs.cpp
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@ -31,7 +31,8 @@ static bool inferAllPrototypeAttributes(
// attribute logic on all calls to declarations (as declarations aren't
// explicitly visited by CGSCC passes in the new pass manager.)
if (F.isDeclaration() && !F.hasOptNone()) {
Changed |= inferLibFuncAttributes(F, GetTLI(F));
if (!F.hasFnAttribute(Attribute::NoBuiltin))
Changed |= inferLibFuncAttributes(F, GetTLI(F));
Changed |= inferAttributesFromOthers(F);
}

5
test/Transforms/InferFunctionAttrs/nobuiltin.ll Normal file
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@ -0,0 +1,5 @@
; RUN: opt -S -inferattrs < %s | FileCheck %s
; CHECK: Function Attrs: nobuiltin allocsize(0)
; CHECK: declare i8* @_Znwm(i32)
declare i8* @_Znwm(i32) nobuiltin allocsize(0)