Add a pass to propagate global constants to other globals (#6287)

SimplifyGlobals already does this, so this is a subset of that pass, and does not
add anything new. It is useful for testing, however.

In particular it allows testing that we propagate subsequent globals in a single
pass, that is if one global reads from another and becomes constant, then it
can be propagated as well. SimplifyGlobals runs multiple passes so this always
worked, but with this pass we can test that we do it efficiently in one pass.

This will also be useful for comparing stringref to imported strings, as it
allows gathered strings to be propagated to other globals (possible with
stringref, but not imported strings) but not anywhere else (which might have
downsides as it could lead to more allocations).

Also add an additional test for simplify-globals that we do not get confused by
an unoptimizable global.get in the middle (see last part).

1 files changed, 3 insertions, 0 deletions

diff --git a/test/lit/help/wasm2js.test b/test/lit/help/wasm2js.test
index 43243b99a..aadefe8fc 100644
--- a/test/lit/help/wasm2js.test
+++ b/test/lit/help/wasm2js.test
@@ -324,6 +324,9 @@
 ;; CHECK-NEXT:   --print-stack-ir                              print out Stack IR (useful for
 ;; CHECK-NEXT:                                                 internal debugging)
 ;; CHECK-NEXT:
+;; CHECK-NEXT:   --propagate-globals-globally                  propagate global values to other
+;; CHECK-NEXT:                                                 globals (useful for tests)
+;; CHECK-NEXT:
 ;; CHECK-NEXT:   --remove-imports                              removes imports and replaces
 ;; CHECK-NEXT:                                                 them with nops
 ;; CHECK-NEXT: