RemoveUnusedModuleElements: Make exports skip trampolines (#6026)

If we export a function that just calls another function, we can export that one
instead. Then the one in the middle may be unused,

function foo() {
  return bar();
}

export foo; // can be an export of bar

This saves a few bytes in rare cases, but probably more important is that it saves
the trampoline, so if this is on a hot path, we save a call.

Context: emscripten-core/emscripten#20478 (comment)

In general this is not needed as inlining helps us out by inlining foo() into the
caller (since foo is tiny, that always ends up happening). But exports are a case
the inliner cannot handle, so we do it here.

1 files changed, 1 insertions, 6 deletions

diff --git a/test/lit/passes/O3_inline-functions-with-loops_flexible-inline-max-function-size=30.wast b/test/lit/passes/O3_inline-functions-with-loops_flexible-inline-max-function-size=30.wast
index e0045579d..907891aee 100644
--- a/test/lit/passes/O3_inline-functions-with-loops_flexible-inline-max-function-size=30.wast
+++ b/test/lit/passes/O3_inline-functions-with-loops_flexible-inline-max-function-size=30.wast
@@ -18,7 +18,7 @@
 
   ;; CHECK:      (export "t1" (func $t1))
 
-  ;; CHECK:      (export "t2" (func $t2))
+  ;; CHECK:      (export "t2" (func $fib))
 
   ;; CHECK:      (export "t3" (func $t3))
 
@@ -155,11 +155,6 @@
       )
     )
   )
-  ;; CHECK:      (func $t2 (; has Stack IR ;) (param $0 i32) (result i32)
-  ;; CHECK-NEXT:  (call $fib
-  ;; CHECK-NEXT:   (local.get $0)
-  ;; CHECK-NEXT:  )
-  ;; CHECK-NEXT: )
   (func $t2 (export "t2") (type $t0) (param $p0 i32) (result i32)
     (call $fib
       (local.get $p0)