[llvm] [SPIR-V] Fix some GEP legalization (PR #150943)

[Nathan Gauër via llvm-commits]

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@@ -1395,6 +1521,13 @@ Instruction *SPIRVEmitIntrinsics::visitSwitchInst(SwitchInst &I) {
 }
 
 Instruction *SPIRVEmitIntrinsics::visitGetElementPtrInst(GetElementPtrInst &I) {
+  if (I.getSourceElementType() == IntegerType::getInt8Ty(CurrF->getContext()) &&
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Keenuts wrote:

Right, wrote this code before restricting to i8, but now seems better to revisit & simplify it

https://github.com/llvm/llvm-project/pull/150943