[all-commits] [llvm/llvm-project] d198c7: [WebAssembly][LiveDebugValues] Handle target index...

[Heejin Ahn via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: d198c75e5ae0415bf457f0d1a46940ee758c6b0d
      https://github.com/llvm/llvm-project/commit/d198c75e5ae0415bf457f0d1a46940ee758c6b0d
  Author: Heejin Ahn <aheejin at gmail.com>
  Date:   2023-01-10 (Tue, 10 Jan 2023)

  Changed paths:
    M llvm/include/llvm/CodeGen/TargetInstrInfo.h
    M llvm/lib/CodeGen/LiveDebugValues/VarLocBasedImpl.cpp
    M llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyMCTargetDesc.h
    M llvm/lib/Target/WebAssembly/WebAssemblyInstrInfo.cpp
    M llvm/lib/Target/WebAssembly/WebAssemblyInstrInfo.h
    M llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp
    M llvm/test/DebugInfo/WebAssembly/live-debug-values.mir

  Log Message:
  -----------
  [WebAssembly][LiveDebugValues] Handle target index defs

This adds the missing handling for defs for target index operands, as is
already done for registers.

There are two kinds of target indices: local indices and stack operands.

- Locals are something similar to registers in Wasm-land. For local
  indices, we can check for local-defining instructions (`local.set` or
  `local.tee`).

- Wasm is a stack machine, so we have values in certain Wasm value stack
  location, which change when Wasm instructions produce or consume
  values. So basically any value-producing instrucion, i.e., instruction
  with defs, can change values in the Wasm stack. But I think we don't
  need to worry about this here, because `WebAssemblyDebugFixup`, which
  runs right before this analysis, makes sure to insert terminating
  `DBG_VALUE $noreg` instructions whenever a stack value gets popped.
  After `WebAssemblyDebugFixup`, there shouldn't be any `DBG_VALUE`s for
  stack operands that don't have a terminating `DBG_VALUE $noreg` within
  the same BB.

So this CL only works on `DBG_VALUE`s for locals. When we encounter a
`local.set` or `local.tee` instructions, we delete `DBG_VALUE`s for
those target index locations from the open range set, so they will not
be availble in `OutLocs`. For example,
```
bb.0:
  successors: %bb.1
  DBG_VALUE target-index(wasm-local) + 2, $noreg, "var", ...
  ...
  local.set 2 ...

bb.1:
; predecessors: %bb.0
  ; We shouldn't add `DBG_VALUE target (wasm-local) + 2 here because
  ; it was killed by 'local.set' in bb.0
```

After disabling register coalescing at -O1, the average PC ranges
covered for Emscripten core benchmarks is currently 20.6% in the LLVM
tot. After applying D138943 and this CL, the coverage goes up to 57%.
This also enables LiveDebugValues analysis in the Wasm pipeline by
default.

Reviewed By: dschuff, jmorse

Differential Revision: https://reviews.llvm.org/D140373