[llvm-dev] LTO and intrinsics mangling

Artur Pilipenko via llvm-dev llvm-dev at lists.llvm.org
Mon Apr 18 09:45:13 PDT 2016

In the current mangling scheme for overloaded intrinsics we include overloaded type names in the intrinsic name. For example:

%struct.foobar = type { i32 }
declare <4 x %struct.foobar*> @llvm.masked.load.v4p0struct.foobar(<4 x %struct.foobar*>*, i32, <4 x i1>, <4 x %struct.foobar*>)

Verifier checks that an overloaded intrinsic name matches with its signature.

When different modules are loaded in LTO configuration with the same LLVMContext, types with the same name from different modules are renamed so their names are unique (%struct.foobar in the second module becomes %struct.foobar.0). After renaming intrinsic names and signatures can become inconsistent.

Usually it slips unnoticed because we don't verify individual modules and eventually map isomorphic types to a single type. So isomorphic types get their original names. Although in some cases it causes problems.

Initially I came across the problem with my recent change which added an overloaded type to the masked load/store intrinsics (http://reviews.llvm.org/D17270). The discrepancy between the name and the signature triggers auto-upgrade bit from my patch converting an incorrect mangling to the correct one. But later after remapping of isomorphic types when we return to the original type name this “updated" intrinsic name become invalid.

Another way to trigger the problem is to have different types with the same name in different modules. Corresponding test case is attached. In this case types in different modules will be renamed but the intrinsics from different modules will have the same name which will be caught by verifier.

As a possible solution we can use AutoUpgrade to handle the situation when the name of the intrinsic doesn't match with its signature. In such cases we have to rename the intrinsic. Then during linking if we map some isomorphic types we have to update intrinsics names. To do that we have to teach IRMover to update intrinsics signatures according to the types mapping.

Does this sound reasonable? Are there any other alternatives?


To reproduce:
$ clang -O3 -S -march=core-avx2 -emit-llvm bar.c
$ clang -O3 -S -march=core-avx2 -emit-llvm foo.c
$ llvm-as bar.ll
$ llvm-as foo.ll
$ llvm-lto foo.bc bar.bc
Invalid user of intrinsic instruction!
<4 x %struct.foobar.0*> (<4 x %struct.foobar.0*>*, i32, <4 x i1>, <4 x %struct.foobar.0*>)* bitcast (<4 x %struct.foobar*> (<4 x %struct.foobar*>*, i32, <4 x i1>, <4 x %struct.foobar*>)* @llvm.masked.load.v4p0struct.foobar to <4 x %struct.foobar.0*> (<4 x %struct.foobar.0*>*, i32, <4 x i1>, <4 x %struct.foobar.0*>)*)
Invalid user of intrinsic instruction!
void (<4 x %struct.foobar.0*>, <4 x %struct.foobar.0*>*, i32, <4 x i1>)* bitcast (void (<4 x %struct.foobar*>, <4 x %struct.foobar*>*, i32, <4 x i1>)* @llvm.masked.store.v4p0struct.foobar to void (<4 x %struct.foobar.0*>, <4 x %struct.foobar.0*>*, i32, <4 x i1>)*)
LLVM ERROR: Broken module found, compilation aborted!
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