[inferattrs] Don't infer lib func attributes for nobuiltin functions
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.
GitOrigin-RevId: 11707435ccb44a9377bfed407453e0646a159636
diff --git a/lib/Transforms/IPO/InferFunctionAttrs.cpp b/lib/Transforms/IPO/InferFunctionAttrs.cpp
index 30402f1..c32e098 100644
--- a/lib/Transforms/IPO/InferFunctionAttrs.cpp
+++ b/lib/Transforms/IPO/InferFunctionAttrs.cpp
@@ -31,7 +31,8 @@
// 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);
}
diff --git a/test/Transforms/InferFunctionAttrs/nobuiltin.ll b/test/Transforms/InferFunctionAttrs/nobuiltin.ll
new file mode 100644
index 0000000..1239a22
--- /dev/null
+++ b/test/Transforms/InferFunctionAttrs/nobuiltin.ll
@@ -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)
