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
This enables `LiveDebugValues` analysis for Wasm. `DBG_VALUE`s expire at
the end of a BB, and this is the analysis extends their lifetime when
possible, greatly increasing the coverage of variable debug info.
Specifically, this removes the current constraint that this analysis is
only used with physical registers, which was first introduced in D18421,
because Wasm uses only virtual registers. I don't think there's anything
inherent in this analysis that only applies to physical registers; it
was just because all targets using this analysis ran this at the end of
their compiliation pipeline, at which point all their vregs had been
allocated, and Wasm's debug info infrastructure was not really set up
yet, so it was not using it.
This adds supports to Wasm-specific target-index operands, defined in
2166d9529a/llvm/lib/Target/WebAssembly/WebAssembly.h (L87-L100).
Among these, `TI_LOCAL`, `TI_LOCAL_INDIRECT`, and `TI_OPERAND_STACK` are
used by Wasm `DBG_VALUE` instructions.
This does not yet handle mutable target indices, i.e., this does not
terminate a `DBG_VALUE` for a local index when we encounter a new
`local.set` or `local.tee`. It will be implemented as a follow-up.
Reviewed By: dschuff, jmorse
Differential Revision: https://reviews.llvm.org/D138943
