[flang][hlfir] Potential excessive stack usage

[vzakhari]

During converting AssignOp to FIR we insert AllocaOp here:

llvm-project/flang/lib/Optimizer/HLFIR/Transforms/ConvertToFIR.cpp

Line 99 in be5f35e

mlir::Value temp = builder.create<fir::AllocaOp>(loc, lhsValueType);

If the AssignOp is inside a loop, this alloca may cause excessive stack usage. We need to either insert stacksave/stackrestore around it or use fir::FirOpBuilder::createTemporary as discussed in https://reviews.llvm.org/D149222.

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[jeanPerier]

Thanks for noticing this. At that level of the flow, I think we should stick to fir::FirOpBuilder::createTemporary, that is what the current lowering is doing.

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