[PATCH] D37874: [TwoAddressInstructionPass] When prepending COPYs when processing tied operands, take the register class constraint from the instruction operands not the register we're copying.

[Craig Topper via Phabricator via llvm-commits]

craig.topper added inline comments.


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Comment at: lib/CodeGen/TwoAddressInstructionPass.cpp:1521-1522
     MIB.addReg(RegB, 0, SubRegB);
-    const TargetRegisterClass *RC = MRI->getRegClass(RegB);
+    const TargetRegisterClass *RC = TII->getRegClass(MI->getDesc(), SrcIdx, TRI,
+                                                     *MF);
     if (SubRegB) {
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arsenm wrote:
> craig.topper wrote:
> > arsenm wrote:
> > > Can't this now fail if the instruction uses an unknown register class operand?
> > Can you give an example? I'm not very familiar with some of this stuff.
> You can define an instruction operand with an unknown register class, e.g. PATCHPOINT uses this:
>   let OutOperandList = (outs unknown:$dst);
> 
> Similarly variable_ops instructions don't have statically known register classes from the operand definition.
How likely is that to be used on a tied operand?


https://reviews.llvm.org/D37874