[llvm-dev] LTO and intrinsics mangling

Philip Reames via llvm-dev llvm-dev at lists.llvm.org
Mon Apr 18 16:22:33 PDT 2016

On 04/18/2016 09:45 AM, Artur Pilipenko via llvm-dev wrote:
> 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.
This seems like a clear bug in the module loading.  If we're changing 
type names, we need to change the intrinsic signatures as well.
> 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?
Given our current intrinsic naming scheme, the approach you've described 
seems entirely reasonable.

An alternate scheme would be to make the intrinsic signatures 
insensitive to the struct naming.  (That was probably a bad idea on my 
part to start with, sorry!)  I would argue that we should not block your 
original change on a re-architecting effort here.
> Artur
> 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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