Commit Graph

3 Commits

Author SHA1 Message Date
Sam Clegg 3b8d2be527 Reland: "[lld][WebAssembly] Initial support merging string data"
This change was originally landed in: 5000a1b4b9
It was reverted in: 061e071d8c

This change adds support for a new WASM_SEG_FLAG_STRINGS flag in
the object format which works in a similar fashion to SHF_STRINGS
in the ELF world.

Unlike the ELF linker this support is currently limited:
- No support for SHF_MERGE (non-string merging)
- Always do full tail merging ("lo" can be merged with "hello")
- Only support single byte strings (p2align 0)

Like the ELF linker merging is only performed at `-O1` and above.

This fixes part of https://bugs.llvm.org/show_bug.cgi?id=48828,
although crucially it doesn't not currently support debug sections
because they are not represented by data segments (they are custom
sections)

Differential Revision: https://reviews.llvm.org/D97657
2021-05-10 16:03:38 -07:00
Nico Weber 061e071d8c Revert "[lld][WebAssembly] Initial support merging string data"
This reverts commit 5000a1b4b9.
Breaks tests, see https://reviews.llvm.org/D97657#2749151

Easily repros locally with `ninja check-llvm-mc-webassembly`.
2021-05-10 18:28:28 -04:00
Sam Clegg 5000a1b4b9 [lld][WebAssembly] Initial support merging string data
This change adds support for a new WASM_SEG_FLAG_STRINGS flag in
the object format which works in a similar fashion to SHF_STRINGS
in the ELF world.

Unlike the ELF linker this support is currently limited:
- No support for SHF_MERGE (non-string merging)
- Always do full tail merging ("lo" can be merged with "hello")
- Only support single byte strings (p2align 0)

Like the ELF linker merging is only performed at `-O1` and above.

This fixes part of https://bugs.llvm.org/show_bug.cgi?id=48828,
although crucially it doesn't not currently support debug sections
because they are not represented by data segments (they are custom
sections)

Differential Revision: https://reviews.llvm.org/D97657
2021-05-10 13:15:12 -07:00