[PATCH] D94355: [SimplifyCFG] Add relative switch lookup tables

[Gulfem Savrun Yeniceri via Phabricator via cfe-commits]

gulfem marked an inline comment as done.
gulfem added a comment.

In D94355#2530225 <https://reviews.llvm.org/D94355#2530225>, @lebedev.ri wrote:

> Can you please add an explanation to the patch's description as to why
> we don't want to instead convert non-relative/relative LUT's elsewhere,
> please.

@mcgrathr gave some explanation to that:

>> Many backends generate PIC-friendly jump tables. This is about generating IR initializers that translate to the same kind of backend assembly expressions as those backends use for their jump tables.

I also want to add to that:
This task specifically tries make switch-to-lookup tables PIC-friendly, but it does not necessarily try to make all the jump tables PIC-friendly.
There is also another work going on to generate PIC-friendly vtables.
Therefore, converting non-relative lookup tables to relative tables elsewhere can be explored as a separate task.



================
Comment at: llvm/lib/Transforms/Utils/SimplifyCFG.cpp:5512-5525
+  // If not in x86 or aarch64 mode, do not generate a relative lookup table.
+  Triple TargetTriple(M.getTargetTriple());
+  if (!(TargetTriple.getArch() == Triple::x86_64 ||
+        TargetTriple.getArch() == Triple::aarch64))
+    return false;
+
+  // If not tiny or small code model, do not generate a relative lookup table.
----------------
lebedev.ri wrote:
> This should be some TLI/TTI hook.
> This should be some TLI/TTI hook.
Could you please elaborate on that?
Are you talking about getting the PIC level?



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