SimplifyGlobals: Constant-propagate constant values of immutable globals

src/passes/SimplifyGlobals.cpp

@@ -21,10 +21,12 @@
 //    globals immutable.
 //  * If an immutable global is a copy of another, use the earlier one,
 //    to allow removal of the copies later.
+//  * Apply the constant values of immutable globals.
 //
 
 #include <atomic>
 
+#include "ir/utils.h"
 #include "pass.h"
 #include "wasm.h"
 
@@ -54,6 +56,7 @@ struct GlobalUseScanner : public WalkerPass<PostWalker<GlobalUseScanner>> {
 };
 
 using NameNameMap = std::map<Name, Name>;
+using NameSet = std::set<Name>;
 
 struct GlobalUseModifier : public WalkerPass<PostWalker<GlobalUseModifier>> {
   bool isFunctionParallel() override { return true; }
@@ -76,6 +79,29 @@ struct GlobalUseModifier : public WalkerPass<PostWalker<GlobalUseModifier>> {
   NameNameMap* copiedParentMap;
 };
 
+struct ConstantGlobalApplier
+  : public WalkerPass<PostWalker<ConstantGlobalApplier>> {
+  bool isFunctionParallel() override { return true; }
+
+  ConstantGlobalApplier(NameSet* constantGlobals)
+    : constantGlobals(constantGlobals) {}
+
+  ConstantGlobalApplier* create() override {
+    return new ConstantGlobalApplier(constantGlobals);
+  }
+
+  void visitGlobalGet(GlobalGet* curr) {
+    if (constantGlobals->count(curr->name)) {
+      auto* global = getModule()->getGlobal(curr->name);
+      assert(global->init->is<Const>());
+      replaceCurrent(ExpressionManipulator::copy(global->init, *getModule()));
+    }
+  }
+
+private:
+  NameSet* constantGlobals;
+};
+
 } // anonymous namespace
 
 struct SimplifyGlobals : public Pass {
@@ -135,6 +161,23 @@ struct SimplifyGlobals : public Pass {
       subRunner.add<GlobalUseModifier>(&copiedParentMap);
       subRunner.run();
     }
+    // If any immutable globals have constant values, we can just apply them
+    // (the global itself will be removed by another pass, as it/ won't have
+    // any uses).
+    NameSet constantGlobals;
+    for (auto& global : module->globals) {
+      if (!global->mutable_ && !global->imported() &&
+          global->init->is<Const>()) {
+        constantGlobals.insert(global->name);
+      }
+    }
+    if (!constantGlobals.empty()) {
+      PassRunner subRunner(module, runner->options);
+      subRunner.add<ConstantGlobalApplier>(&constantGlobals);
+      subRunner.run();
+    }
+    // TODO a mutable global's initial value can be applied to another global
+    // after it, as the mutable one can't mutate during instance startup
   }
 };
 

test/min.fromasm

@@ -2,7 +2,6 @@
  (import "env" "memory" (memory $memory 256 256))
  (data (global.get $__memory_base) "min.asm.js")
  (import "env" "__memory_base" (global $__memory_base i32))
- (global $M i32 (i32.const 0))
  (export "floats" (func $floats))
  (export "getTempRet0" (func $ub))
  (export "neg" (func $neg))
@@ -35,6 +34,6 @@
   (drop
    (call $ub)
   )
-  (global.get $M)
+  (i32.const 0)
  )
 )

test/min.fromasm.clamp

@@ -2,7 +2,6 @@
  (import "env" "memory" (memory $memory 256 256))
  (data (global.get $__memory_base) "min.asm.js")
  (import "env" "__memory_base" (global $__memory_base i32))
- (global $M i32 (i32.const 0))
  (export "floats" (func $floats))
  (export "getTempRet0" (func $ub))
  (export "neg" (func $neg))
@@ -35,6 +34,6 @@
   (drop
    (call $ub)
   )
-  (global.get $M)
+  (i32.const 0)
  )
 )

test/min.fromasm.imprecise

@@ -1,6 +1,5 @@
 (module
  (import "env" "memory" (memory $memory 256 256))
- (global $M i32 (i32.const 0))
  (export "floats" (func $floats))
  (export "getTempRet0" (func $ub))
  (export "neg" (func $neg))
@@ -33,6 +32,6 @@
   (drop
    (call $ub)
   )
-  (global.get $M)
+  (i32.const 0)
  )
 )

test/passes/simplify-globals_enable-mutable-globals.txt

@@ -51,3 +51,62 @@
  (global $g2 (mut i32) (global.get $g1))
  (export "global-2" (global $g2))
 )
+(module
+ (type $FUNCSIG$v (func))
+ (global $g1 i32 (i32.const 1))
+ (global $g2 i32 (global.get $g1))
+ (global $g3 f64 (f64.const -3.4))
+ (global $g4 f64 (f64.const -2.8))
+ (global $g5 i32 (i32.const 2))
+ (global $g6 i32 (global.get $g5))
+ (global $g7 i32 (i32.const 3))
+ (global $g8 i32 (global.get $g7))
+ (global $g9 i32 (i32.const 4))
+ (global $ga (mut i32) (global.get $g9))
+ (global $gb (mut i32) (i32.const 5))
+ (global $gc i32 (global.get $gb))
+ (func $foo (; 0 ;) (type $FUNCSIG$v)
+  (drop
+   (i32.const 1)
+  )
+  (drop
+   (i32.const 1)
+  )
+  (drop
+   (f64.const -3.4)
+  )
+  (drop
+   (f64.const -2.8)
+  )
+  (drop
+   (i32.const 2)
+  )
+  (drop
+   (i32.const 2)
+  )
+  (drop
+   (i32.const 3)
+  )
+  (drop
+   (i32.const 3)
+  )
+  (drop
+   (i32.const 4)
+  )
+  (drop
+   (global.get $ga)
+  )
+  (drop
+   (global.get $gb)
+  )
+  (drop
+   (global.get $gc)
+  )
+  (global.set $ga
+   (i32.const 6)
+  )
+  (global.set $gb
+   (i32.const 7)
+  )
+ )
+)

test/passes/simplify-globals_enable-mutable-globals.wast

@@ -34,4 +34,34 @@
   (global $g2 (mut i32) (global.get $g1))
   (export "global-2" (global $g2))
 )
+(module
+  (global $g1 i32 (i32.const 1))
+  (global $g2 i32 (global.get $g1))
+  (global $g3 f64 (f64.const -3.4))
+  (global $g4 (mut f64) (f64.const -2.8))
+  (global $g5 i32 (i32.const 2))
+  (global $g6 (mut i32) (global.get $g5))
+  (global $g7 (mut i32) (i32.const 3))
+  (global $g8 i32 (global.get $g7))
+  (global $g9 i32 (i32.const 4))
+  (global $ga (mut i32) (global.get $g9))
+  (global $gb (mut i32) (i32.const 5))
+  (global $gc i32 (global.get $gb))
+  (func $foo
+   (drop (global.get $g1))
+   (drop (global.get $g2))
+   (drop (global.get $g3))
+   (drop (global.get $g4))
+   (drop (global.get $g5))
+   (drop (global.get $g6))
+   (drop (global.get $g7))
+   (drop (global.get $g8))
+   (drop (global.get $g9))
+   (drop (global.get $ga))
+   (drop (global.get $gb))
+   (drop (global.get $gc))
+   (global.set $ga (i32.const 6))
+   (global.set $gb (i32.const 7))
+  )
+)
 

test/unit.fromasm

@@ -24,7 +24,6 @@
  (import "asm2wasm" "f64-to-int" (func $f64-to-int (param f64) (result i32)))
  (import "asm2wasm" "f64-rem" (func $f64-rem (param f64 f64) (result f64)))
  (global $Int (mut i32) (i32.const 0))
- (global $Double f64 (f64.const 0))
  (global $nonZero (mut i32) (i32.const 1337))
  (global $exportedNumber i32 (i32.const 42))
  (export "big_negative" (func $big_negative))
@@ -92,7 +91,7 @@
   )
   (if
    (f64.gt
-    (global.get $Double)
+    (f64.const 0)
     (f64.const 0)
    )
    (return

test/unit.fromasm.clamp

@@ -22,7 +22,6 @@
  (import "env" "emscripten_log" (func $emscripten_log))
  (import "asm2wasm" "f64-rem" (func $f64-rem (param f64 f64) (result f64)))
  (global $Int (mut i32) (i32.const 0))
- (global $Double f64 (f64.const 0))
  (global $nonZero (mut i32) (i32.const 1337))
  (global $exportedNumber i32 (i32.const 42))
  (export "big_negative" (func $big_negative))
@@ -90,7 +89,7 @@
   )
   (if
    (f64.gt
-    (global.get $Double)
+    (f64.const 0)
     (f64.const 0)
    )
    (return

test/unit.fromasm.imprecise

@@ -20,7 +20,6 @@
  (import "env" "emscripten_log" (func $emscripten_log))
  (import "asm2wasm" "f64-rem" (func $f64-rem (param f64 f64) (result f64)))
  (global $Int (mut i32) (i32.const 0))
- (global $Double f64 (f64.const 0))
  (global $nonZero (mut i32) (i32.const 1337))
  (global $exportedNumber i32 (i32.const 42))
  (export "big_negative" (func $big_negative))
@@ -88,7 +87,7 @@
   )
   (if
    (f64.gt
-    (global.get $Double)
+    (f64.const 0)
     (f64.const 0)
    )
    (return