Reintroduce wasm-merge (#5709)

We used to have a wasm-merge tool but removed it for a lack of use cases. Recently
use cases have been showing up in the wasm GC space and elsewhere, as people are
using more diverse toolchains together, for example a project might build some C++
code alongside some wasm GC code. Merging those wasm files together can allow
for nice optimizations like inlining and better DCE etc., so it makes sense to have a
tool for merging.

Background:
* Removal: #1969
* Requests:
  * wasm-merge - why it has been deleted #2174
  * Compiling and linking wat files #2276
  * wasm-link? #2767

This PR is a compete rewrite of wasm-merge, not a restoration of the original
codebase. The original code was quite messy (my fault), and also, since then
we've added multi-memory and multi-table which makes things a lot simpler.

The linking semantics are as described in the "wasm-link" issue #2767 : all we do
is merge normal wasm files together and connect imports and export. That is, we
have a graph of modules and their names, and each import to a module name can
be resolved to that module. Basically, like a JS bundler would do for JS, or, in other
words, we do the same operations as JS code would do to glue wasm modules
together at runtime, but at compile time. See the README update in this PR for a
concrete example.

There are no plans to do more than that simple bundling, so this should not
really overlap with wasm-ld's use cases.

This should be fairly fast as it works in linear time on the total input code. However,
it won't be as fast as wasm-ld, of course, as it does build Binaryen IR for each
module. An advantage to working on Binaryen IR is that we can easily do some
global DCE after merging, and further optimizations are possible later.

1 files changed, 149 insertions, 0 deletions

diff --git a/test/lit/help/wasm-merge.test b/test/lit/help/wasm-merge.test
new file mode 100644
index 000000000..541f37d5a
--- /dev/null
+++ b/test/lit/help/wasm-merge.test
@@ -0,0 +1,149 @@
+;; RUN: wasm-merge --help | filecheck %s
+;; CHECK: ================================================================================
+;; CHECK-NEXT: wasm-merge INFILE1 NAME1 INFILE2 NAME2 [..]
+;; CHECK-NEXT:
+;; CHECK-NEXT: Merge wasm files into one.
+;; CHECK-NEXT:
+;; CHECK-NEXT: For example,
+;; CHECK-NEXT:
+;; CHECK-NEXT:   wasm-merge foo.wasm foo bar.wasm bar -o merged.wasm
+;; CHECK-NEXT:
+;; CHECK-NEXT: will read foo.wasm and bar.wasm, with names 'foo' and 'bar' respectively, so if
+;; CHECK-NEXT: the second imports from 'foo', we will see that as an import from the first
+;; CHECK-NEXT: module after the merge. The merged output will be written to merged.wasm.
+;; CHECK-NEXT:
+;; CHECK-NEXT: Note that filenames and modules names are interleaved (which is hopefully less
+;; CHECK-NEXT: confusing).
+;; CHECK-NEXT: ================================================================================
+;; CHECK-NEXT:
+;; CHECK-NEXT:
+;; CHECK-NEXT: wasm-merge options:
+;; CHECK-NEXT: -------------------
+;; CHECK-NEXT:
+;; CHECK-NEXT:   --output,-o                          Output file (stdout if not specified)
+;; CHECK-NEXT:
+;; CHECK-NEXT:   --rename-export-conflicts,-rec       Rename exports to avoid conflicts (rather
+;; CHECK-NEXT:                                        than error)
+;; CHECK-NEXT:
+;; CHECK-NEXT:   --skip-export-conflicts,-sec         Skip exports that conflict with previous
+;; CHECK-NEXT:                                        ones
+;; CHECK-NEXT:
+;; CHECK-NEXT:   --emit-text,-S                       Emit text instead of binary for the
+;; CHECK-NEXT:                                        output file
+;; CHECK-NEXT:
+;; CHECK-NEXT:   --debuginfo,-g                       Emit names section and debug info
+;; CHECK-NEXT:
+;; CHECK-NEXT:
+;; CHECK-NEXT: Tool options:
+;; CHECK-NEXT: -------------
+;; CHECK-NEXT:
+;; CHECK-NEXT:   --mvp-features,-mvp                  Disable all non-MVP features
+;; CHECK-NEXT:
+;; CHECK-NEXT:   --all-features,-all                  Enable all features
+;; CHECK-NEXT:
+;; CHECK-NEXT:   --detect-features                    (deprecated - this flag does nothing)
+;; CHECK-NEXT:
+;; CHECK-NEXT:   --quiet,-q                           Emit less verbose output and hide trivial
+;; CHECK-NEXT:                                        warnings.
+;; CHECK-NEXT:
+;; CHECK-NEXT:   --experimental-poppy                 Parse wast files as Poppy IR for testing
+;; CHECK-NEXT:                                        purposes.
+;; CHECK-NEXT:
+;; CHECK-NEXT:   --enable-sign-ext                    Enable sign extension operations
+;; CHECK-NEXT:
+;; CHECK-NEXT:   --disable-sign-ext                   Disable sign extension operations
+;; CHECK-NEXT:
+;; CHECK-NEXT:   --enable-threads                     Enable atomic operations
+;; CHECK-NEXT:
+;; CHECK-NEXT:   --disable-threads                    Disable atomic operations
+;; CHECK-NEXT:
+;; CHECK-NEXT:   --enable-mutable-globals             Enable mutable globals
+;; CHECK-NEXT:
+;; CHECK-NEXT:   --disable-mutable-globals            Disable mutable globals
+;; CHECK-NEXT:
+;; CHECK-NEXT:   --enable-nontrapping-float-to-int    Enable nontrapping float-to-int
+;; CHECK-NEXT:                                        operations
+;; CHECK-NEXT:
+;; CHECK-NEXT:   --disable-nontrapping-float-to-int   Disable nontrapping float-to-int
+;; CHECK-NEXT:                                        operations
+;; CHECK-NEXT:
+;; CHECK-NEXT:   --enable-simd                        Enable SIMD operations and types
+;; CHECK-NEXT:
+;; CHECK-NEXT:   --disable-simd                       Disable SIMD operations and types
+;; CHECK-NEXT:
+;; CHECK-NEXT:   --enable-bulk-memory                 Enable bulk memory operations
+;; CHECK-NEXT:
+;; CHECK-NEXT:   --disable-bulk-memory                Disable bulk memory operations
+;; CHECK-NEXT:
+;; CHECK-NEXT:   --enable-exception-handling          Enable exception handling operations
+;; CHECK-NEXT:
+;; CHECK-NEXT:   --disable-exception-handling         Disable exception handling operations
+;; CHECK-NEXT:
+;; CHECK-NEXT:   --enable-tail-call                   Enable tail call operations
+;; CHECK-NEXT:
+;; CHECK-NEXT:   --disable-tail-call                  Disable tail call operations
+;; CHECK-NEXT:
+;; CHECK-NEXT:   --enable-reference-types             Enable reference types
+;; CHECK-NEXT:
+;; CHECK-NEXT:   --disable-reference-types            Disable reference types
+;; CHECK-NEXT:
+;; CHECK-NEXT:   --enable-multivalue                  Enable multivalue functions
+;; CHECK-NEXT:
+;; CHECK-NEXT:   --disable-multivalue                 Disable multivalue functions
+;; CHECK-NEXT:
+;; CHECK-NEXT:   --enable-gc                          Enable garbage collection
+;; CHECK-NEXT:
+;; CHECK-NEXT:   --disable-gc                         Disable garbage collection
+;; CHECK-NEXT:
+;; CHECK-NEXT:   --enable-memory64                    Enable memory64
+;; CHECK-NEXT:
+;; CHECK-NEXT:   --disable-memory64                   Disable memory64
+;; CHECK-NEXT:
+;; CHECK-NEXT:   --enable-gc-nn-locals                Enable GC non-null locals
+;; CHECK-NEXT:
+;; CHECK-NEXT:   --disable-gc-nn-locals               Disable GC non-null locals
+;; CHECK-NEXT:
+;; CHECK-NEXT:   --enable-relaxed-simd                Enable relaxed SIMD
+;; CHECK-NEXT:
+;; CHECK-NEXT:   --disable-relaxed-simd               Disable relaxed SIMD
+;; CHECK-NEXT:
+;; CHECK-NEXT:   --enable-extended-const              Enable extended const expressions
+;; CHECK-NEXT:
+;; CHECK-NEXT:   --disable-extended-const             Disable extended const expressions
+;; CHECK-NEXT:
+;; CHECK-NEXT:   --enable-strings                     Enable strings
+;; CHECK-NEXT:
+;; CHECK-NEXT:   --disable-strings                    Disable strings
+;; CHECK-NEXT:
+;; CHECK-NEXT:   --enable-multi-memories              Enable multi-memories
+;; CHECK-NEXT:
+;; CHECK-NEXT:   --disable-multi-memories             Disable multi-memories
+;; CHECK-NEXT:
+;; CHECK-NEXT:   --enable-typed-function-references   Deprecated compatibility flag
+;; CHECK-NEXT:
+;; CHECK-NEXT:   --disable-typed-function-references  Deprecated compatibility flag
+;; CHECK-NEXT:
+;; CHECK-NEXT:   --no-validation,-n                   Disables validation, assumes inputs are
+;; CHECK-NEXT:                                        correct
+;; CHECK-NEXT:
+;; CHECK-NEXT:   --pass-arg,-pa                       An argument passed along to optimization
+;; CHECK-NEXT:                                        passes being run. Must be in the form
+;; CHECK-NEXT:                                        KEY@VALUE
+;; CHECK-NEXT:
+;; CHECK-NEXT:   --closed-world,-cw                   Assume code outside of the module does
+;; CHECK-NEXT:                                        not inspect or interact with GC and
+;; CHECK-NEXT:                                        function references, even if they are
+;; CHECK-NEXT:                                        passed out. The outside may hold on to
+;; CHECK-NEXT:                                        them and pass them back in, but not
+;; CHECK-NEXT:                                        inspect their contents or call them.
+;; CHECK-NEXT:
+;; CHECK-NEXT:
+;; CHECK-NEXT: General options:
+;; CHECK-NEXT: ----------------
+;; CHECK-NEXT:
+;; CHECK-NEXT:   --version                            Output version information and exit
+;; CHECK-NEXT:
+;; CHECK-NEXT:   --help,-h                            Show this help message and exit
+;; CHECK-NEXT:
+;; CHECK-NEXT:   --debug,-d                           Print debug information to stderr
+;; CHECK-NEXT: