[PATCH] D78717: [SystemZ] Implement -fstack-clash-protection

[Jonas Paulsson via Phabricator via llvm-commits]

jonpa added a comment.

I experimented with inserting the probing directly in emitPrologue() instead of building the call with metadata, but then came back to the case with a single block function. Looking closer at this, it seems that this could be the motivation behind using the call/metadata stub. Splitting the Prologue/Epilogue block to insert the loop would cause the RestoreBlocks set of PEI to be incorrect, since the epilogue block has changed from MBB to DoneMBB (block after the loop / second half of original MBB).

This could theoretically be fixed by rearranging things so that MBB ended up to have the same instructions and the same place as DoneMBB now gets, but that seems impractical and besides that would break the SaveBlocks set of PEI... (I think perhaps a comment explaining this would be nice.)

There is an assert for the metadata attached to the call instruction, which kind of guards against users defining a function with the same name. Normally, I would have expected a pseudo MachineInstruction to be built here with an immediate operand for the size requirement...


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