[PATCH] D68488: [PATCH 03/27] [noalias] [IR] Introduce ptr_provenance for LoadInst/StoreInst

[Jeroen Dobbelaere via Phabricator via llvm-commits]

jeroen.dobbelaere added a comment.

I have 3 variants of this patch:

- variant 0 : always reserve place for the ptr_provenance; Introduce NumOfOperandsDelta to get the correct number of operands
  - extra space overhead for load/store instructions;
  - extra instruction overhead for ALL instructions ('getNumOperand()');
  - low overhead when adding/removing ptr_provenance
  - NOTE: this is the current provided patch
- variant 1 : always reserve place for the ptr_provenance; Move arguments around when adding/removing ptr_provenance
  - extra space overhead for load/store instructions;
  - NO impact on other instructions;
  - slightly more overhead when accessing operands of load/store instructions;
  - medium overhead when adding/removing ptr_provenance
- variant 2 : Have a LoadInst, LoadWithProvInst and StoreInst, StoreWithProvInst. Only the 'WithProv' variant reserves place for optional argument. When the ptr_provenance is added, it can involve  creating a Load/StoreWithProv based on the original Load/Store. Adding/removing the ptr_provenance argument involves moving arguments around.
  - extra space only needed when we know we will need it.
  - NO impact on other instructions;
  - slightly more overhead when accessing operands of load/store instructions;
  - medium to high overhead when adding ptr_provenance. medium when removing it.
  - higher risk in keeping things correct in optimization: adding the ptr_provenance can require recreating the Load/Store instruction. This might be difficult if the optimization pass is tracking pointers to the original Load/Store instruction.
  - main benefit: almost no impact from this change if the feature is not used (aka -fno-full-restrict)

Any preference in the way forward ? variant 1 is the easy one, as it is just a drop-in. Variant 2 is at the moment less-stable as it requires changes in all optimization passes that need to track the ptr_provenance.


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  https://reviews.llvm.org/D68488/new/

https://reviews.llvm.org/D68488