Stop propagating/inlining string constants (#6234)

This causes overhead atm since in VMs executing a string.const will actually allocate a
string, and more copies means more allocations. For now, just do not add more. This
required changes to two passes: SimplifyGlobals and Precompute.

1 files changed, 65 insertions, 0 deletions

diff --git a/test/lit/passes/simplify-globals-strings.wast b/test/lit/passes/simplify-globals-strings.wast
new file mode 100644
index 000000000..813e2964c
--- /dev/null
+++ b/test/lit/passes/simplify-globals-strings.wast
@@ -0,0 +1,65 @@
+;; NOTE: Assertions have been generated by update_lit_checks.py --all-items and should not be edited.
+;; NOTE: This test was ported using port_passes_tests_to_lit.py and could be cleaned up.
+
+;; We do not "inline" strings from globals, as that might cause more
+;; allocations to happen. TODO if VMs optimize that, remove this
+
+;; RUN: foreach %s %t wasm-opt --simplify-globals -all -S -o - | filecheck %s
+
+;; Also test with -O3 --gufa to see that no other pass does this kind of thing,
+;; as extra coverage.
+
+;; RUN: foreach %s %t wasm-opt -O3 --gufa         -all -S -o - | filecheck %s --check-prefix=O3GUF
+
+(module
+  ;; CHECK:      (type $0 (func (result anyref)))
+
+  ;; CHECK:      (global $string stringref (string.const "one"))
+  ;; O3GUF:      (type $0 (func (result anyref)))
+
+  ;; O3GUF:      (global $string (ref string) (string.const "one"))
+  (global $string stringref (string.const "one"))
+
+  ;; CHECK:      (global $string-mut (mut stringref) (string.const "two"))
+  ;; O3GUF:      (global $string-mut (mut (ref string)) (string.const "two"))
+  (global $string-mut (mut stringref) (string.const "two"))
+
+  ;; CHECK:      (export "global" (func $global))
+  ;; O3GUF:      (export "global" (func $global))
+  (export "global" (func $global))
+
+  ;; CHECK:      (export "written" (func $written))
+  ;; O3GUF:      (export "written" (func $written))
+  (export "written" (func $written))
+
+  ;; CHECK:      (func $global (type $0) (result anyref)
+  ;; CHECK-NEXT:  (global.get $string)
+  ;; CHECK-NEXT: )
+  ;; O3GUF:      (func $global (type $0) (result anyref)
+  ;; O3GUF-NEXT:  (global.get $string)
+  ;; O3GUF-NEXT: )
+  (func $global (result anyref)
+    ;; This should not turn into "one".
+    (global.get $string)
+  )
+
+  ;; CHECK:      (func $written (type $0) (result anyref)
+  ;; CHECK-NEXT:  (global.set $string-mut
+  ;; CHECK-NEXT:   (string.const "three")
+  ;; CHECK-NEXT:  )
+  ;; CHECK-NEXT:  (global.get $string-mut)
+  ;; CHECK-NEXT: )
+  ;; O3GUF:      (func $written (type $0) (result anyref)
+  ;; O3GUF-NEXT:  (global.set $string-mut
+  ;; O3GUF-NEXT:   (string.const "three")
+  ;; O3GUF-NEXT:  )
+  ;; O3GUF-NEXT:  (global.get $string-mut)
+  ;; O3GUF-NEXT: )
+  (func $written (result anyref)
+    (global.set $string-mut
+      (string.const "three")
+    )
+    ;; This should not turn into "three".
+    (global.get $string-mut)
+  )
+)