[PATCH] D67602: GlobalISel: Handle llvm.read_register

[Matt Arsenault via Phabricator via llvm-commits]

arsenm marked an inline comment as done.
arsenm added inline comments.


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Comment at: lib/CodeGen/GlobalISel/IRTranslator.cpp:1529
+    EVT VT = TLI->getValueType(*DL, CI.getType());
+    Register Reg = TLI->getRegisterByName(RegStr->getString().data(), VT, *MF);
+    if (!Reg.isValid())
----------------
paquette wrote:
> rengolin wrote:
> > paquette wrote:
> > > `TLI->getRegisterByName` can't handle sysregs on the AArch64 side, since they're modelled as immediate operands. So, this approach can't work for AArch64.
> > > 
> > > (see llvm/test/CodeGen/AArch64/special-reg.ll for an example)
> > By design, they can only get the stack pointer, I think on any target. It should be an assembler error otherwise.
> I don't think that's true in AArch64. E.g.:
> 
> https://reviews.llvm.org/D53115
> 
> The test added there uses read/write_register to access other special registers. This change made the test added there fail.
> 
> There's also the special-reg.ll test I mentioned above which has stuff like this:
> 
> ```
> %reg = call i64 @llvm.read_register.i64(metadata !1)
> ...
> !1 = !{!"daif"}
> ```
> 
> Which is supposed to produce this (which does not involve SP):
> 
> ```
> mrs x0, DAIF
> ```
> 
> So I don't think that the stack pointer is the only thing we have to think about here. (Unless I'm seriously misunderstanding something, which is entirely possible. :P)
> 
We use this for the EXEC mask (with the special consideration that the call site needs to be marked convergent)


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  https://reviews.llvm.org/D67602/new/

https://reviews.llvm.org/D67602