Inlining: Always inline single-use functions (#3730)

This implements emscripten-core/emscripten#13744

Inlining functions with a single use allows us to remove the function afterward.
That looks highly beneficial, shrinking every single benchmark in emscripten's
benchmark suite, by an average of 2% on the macrobenchmarks and 3.5% on
all of them. Speed also improves, although mostly on the microbenchmarks so
that might be less realistic.

There may be a slight downside to startup time due to emitting larger functions,
but given the baseline compilers in VMs these days it seems worth it, as the
delay would be just to get to the upper tier. On the benchmark suite the risk
seems low.

See more details in the PR above.

1 files changed, 4 insertions, 5 deletions

diff --git a/src/tools/optimization-options.h b/src/tools/optimization-options.h
index 4f5c9e0d1..0e6157473 100644
--- a/src/tools/optimization-options.h
+++ b/src/tools/optimization-options.h
@@ -155,13 +155,12 @@ struct OptimizationOptions : public ToolOptions {
       .add("--one-caller-inline-max-function-size",
            "-ocimfs",
            "Max size of functions that are inlined when there is only one "
-           "caller (default " +
-             std::to_string(InliningOptions().oneCallerInlineMaxSize) +
-             "). Reason this is not unbounded is that some "
-             "implementations may have a hard time optimizing really large "
-             "functions",
+           "caller (default -1, which means all such functions are inlined)",
            Options::Arguments::One,
            [this](Options* o, const std::string& argument) {
+             static_assert(InliningOptions().oneCallerInlineMaxSize ==
+                             Index(-1),
+                           "the help text here is written to assume -1");
              passOptions.inlining.oneCallerInlineMaxSize =
                static_cast<Index>(atoi(argument.c_str()));
            })