[llvm] [SPIR-V] Prevent generating OpTypePointer with OpTypeFunction pointee without extension (PR #207347)

[Juan Manuel Martinez Caamaño via llvm-commits]

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@@ -258,7 +258,9 @@ static void insertBitcasts(MachineFunction &MF, SPIRVGlobalRegistry *GR,
       Register Source = MI.getOperand(2).getReg();
       Type *ElemTy = getMDOperandAsType(MI.getOperand(3).getMetadata(), 0);
       auto SC =
-          isa<FunctionType>(ElemTy)
+          isa<FunctionType>(ElemTy) &&
+                  ST->canUseExtension(
+                      SPIRV::Extension::SPV_INTEL_function_pointers)
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jmmartinez wrote:

Wider question, but I don't have the whole context: why do we attempt to support function pointers when `SPV_INTEL_function_pointers` is not allowed?

I get why it could be useful, but is it really worth the pain we're inflicting on us by trying to hack around this extension not being present?

I would like to (at ir-level) replace all non-function call uses of functions as `poison` if the extension is not used.

@MrSidims @maarquitos14 

https://github.com/llvm/llvm-project/pull/207347