[all-commits] [llvm/llvm-project] 6cca23: [SPIRV] Prevent creation of jump tables from switc...

[Vyacheslav Levytskyy via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 6cca23a3b91e12c0b6639449bc1e5eb564067db3
      https://github.com/llvm/llvm-project/commit/6cca23a3b91e12c0b6639449bc1e5eb564067db3
  Author: Vyacheslav Levytskyy <89994100+VyacheslavLevytskyy at users.noreply.github.com>
  Date:   2024-02-22 (Thu, 22 Feb 2024)

  Changed paths:
    M llvm/lib/Target/SPIRV/SPIRVISelLowering.h
    A llvm/test/CodeGen/SPIRV/switch-no-jump-table.ll

  Log Message:
  -----------
  [SPIRV] Prevent creation of jump tables from switch (#82287)

This PR is to prevent creation of jump tables from switch. The reason is
that SPIR-V doesn't know how to lower jump tables, and a sequence of
commands that IRTranslator generates for switch via jump tables breaks
SPIR-V Backend code generation with complains to G_BRJT. The next
example is the shortest code to break SPIR-V Backend code generation in
this way:

```
target datalayout = "e-i64:64-v16:16-v24:32-v32:32-v48:64-v96:128-v192:256-v256:256-v512:512-v1024:1024-n8:16:32:64"
target triple = "spir64-unknown-unknown"

define spir_func void @foo(i32 noundef %val) {
entry:
  switch i32 %val, label %sw.epilog [
    i32 0, label %sw.bb
    i32 1, label %sw.bb2
    i32 2, label %sw.bb3
    i32 3, label %sw.bb4
  ]
sw.bb:
  br label %sw.epilog
sw.bb2:
  br label %sw.epilog
sw.bb3:
  br label %sw.epilog
sw.bb4:
  br label %sw.epilog
sw.epilog:
  ret void
}
```

To resolve the issue we set a high lower limit for number of blocks in a
jump table via getMinimumJumpTableEntries() and prevent undesirable (or
rather unsupported at the moment) path of code generation.



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