Commits on Jun 18, 2024

1. [WebAssembly] Treat 'rethrow' as terminator in custom isel …

   `rethrow` instruction is a terminator, but when when its DAG is built in
   `SelectionDAGBuilder` in a custom routine, it was NOT treated as such.
   
   ```ll
   rethrow:                                          ; preds = %catch.start
     invoke void @llvm.wasm.rethrow() llvm#1 [ "funclet"(token %1) ]
             to label %unreachable unwind label %ehcleanup
   
   ehcleanup:                                        ; preds = %rethrow, %catch.dispatch
     %tmp = phi i32 [ 10, %catch.dispatch ], [ 20, %rethrow ]
     ...
   ```
   
   In this bitcode, because of the `phi`, a `CONST_I32` will be created
   in the `rethrow` BB. Without this patch, the DAG for the `rethrow` BB
   looks like this:
   ```
     t0: ch,glue = EntryToken
         t3: ch = CopyToReg t0, Register:i32 %9, Constant:i32<20>
         t5: ch = llvm.wasm.rethrow t0, TargetConstant:i32<12161>
       t6: ch = TokenFactor t3, t5
     t8: ch = br t6, BasicBlock:ch<unreachable 0x562532e43c50>
   ```
   Note that `CopyToReg` and `llvm.wasm.rethrow` don't have dependence so
   either can come first in the selected code, which can result in the code
   like
   ```mir
   bb.3.rethrow:
     RETHROW 0, implicit-def dead $arguments
     %9:i32 = CONST_I32 20, implicit-def dead $arguments
     BR %bb.6, implicit-def dead $arguments
   ```
   
   After this patch, `llvm.wasm.rethrow` is treated as a terminator, and
   the DAG will look like
   ```
           t0: ch,glue = EntryToken
         t3: ch = CopyToReg t0, Register:i32 %9, Constant:i32<20>
       t5: ch = llvm.wasm.rethrow t3, TargetConstant:i32<12161>
     t7: ch = br t5, BasicBlock:ch<unreachable 0x5555e3d32c70>
   ```
   Note that now `rethrow` takes a token from `CopyToReg`, so `rethrow` has
   to come after `CopyToReg`. And the resulting code will be
   ```mir
   bb.3.rethrow:
     %9:i32 = CONST_I32 20, implicit-def dead $arguments
     RETHROW 0, implicit-def dead $arguments
     BR %bb.6, implicit-def dead $arguments
   ```
   
   I'm not very familiar with the internals of `getRoot` vs.
   `getControlRoot`, but other terminator instructions seem to use the
   latter, and using it for `rethrow` too worked.

   

   aheejin committed Jun 18, 2024
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