[SPIR-V] Unexpected label emitted in SPIRVAsmPrinter when debug info is present

[seven-mile]

I used -g to emit debug info in Clang and get a LLVM IR module. When I tried to invoke llc and use SPIR-V backend to emit the final SPIR-V, an unexpected label is emitted after OpFunctionEnd:

... omitted
        OpBranchConditional %56 %61 %59
        %59 = OpLabel
        OpReturn
        OpFunctionEnd
Lfunc_end0:
                                        ; -- End function

, which prevented the SPIR-V to be consumed by spirv-as. After disabling -g, the label is gone. I believe it's caused by these lines in the base class AsmPrinter:

llvm-project/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp

Lines 1945 to 1949 in 9a227ba

	if (EmitFunctionSize || needFuncLabels(*MF, *this)) {
	// Create a symbol for the end of function.
	CurrentFnEnd = createTempSymbol("func_end");
	OutStreamer->emitLabel(CurrentFnEnd);
	}

We need some overrides to disable this behaviour for SPIR-V.

[VyacheslavLevytskyy]

@seven-mile Thank you for the report! I don't see any good workarounds using existing hooks/overrides. needFuncLabels() is always true if we have debug info, and a flag for the debug info is private (

llvm-project/llvm/include/llvm/CodeGen/AsmPrinter.h

Line 229 in 9a227ba

bool DbgInfoAvailable = false;

).

A path that I see is that we fix it as a part of AsmPrinter.cpp itself by checking !TT.isSPIRV() before emitting a label after the function body and referring to the SPIR-V specification that supports label instructions only inside a block, not after the function body.

[seven-mile]

Resolved by #107013