use effective shifts in more places in optimize-instructions

Author: kripken

src/ast/bits.h

@@ -51,7 +51,8 @@ struct Bits {
     WASM_UNREACHABLE();
   }
 
-  static Index getEffectiveShifts(Const* amount) {
+  static Index getEffectiveShifts(Expression* expr) {
+    auto* amount = expr->cast<Const>();
     if (amount->type == i32) {
       return getEffectiveShifts(amount->value.geti32(), i32);
     } else if (amount->type == i64) {

src/ast/properties.h

@@ -79,7 +79,7 @@ struct Properties {
 
   // gets the size of the sign-extended value
   static Index getSignExtBits(Expression* curr) {
-    return 32 - curr->cast<Binary>()->right->cast<Const>()->value.geti32();
+    return 32 - Bits::getEffectiveShifts(curr->cast<Binary>()->right);
   }
 
   // Check if an expression is almost a sign-extend: perhaps the inner shift
@@ -93,7 +93,7 @@ struct Properties {
             if (auto* inner = outer->left->dynCast<Binary>()) {
               if (inner->op == ShlInt32) {
                 if (auto* innerConst = inner->right->dynCast<Const>()) {
-                  if (outerConst->value.leU(innerConst->value).geti32()) {
+                  if (Bits::getEffectiveShifts(outerConst) <= Bits::getEffectiveShifts(innerConst)) {
                     return inner->left;
                   }
                 }
@@ -109,8 +109,8 @@ struct Properties {
   // gets the size of the almost sign-extended value, as well as the
   // extra shifts, if any
   static Index getAlmostSignExtBits(Expression* curr, Index& extraShifts) {
-    extraShifts = curr->cast<Binary>()->left->cast<Binary>()->right->cast<Const>()->value.geti32() -
-                  curr->cast<Binary>()->right->cast<Const>()->value.geti32();
+    extraShifts = Bits::getEffectiveShifts(curr->cast<Binary>()->left->cast<Binary>()->right) -
+                  Bits::getEffectiveShifts(curr->cast<Binary>()->right);
     return getSignExtBits(curr);
   }
 

src/passes/OptimizeInstructions.cpp

@@ -779,7 +779,7 @@ struct OptimizeInstructions : public WalkerPass<PostWalker<OptimizeInstructions,
           return;
         } else if (binary->op == ShlInt32) {
           if (auto* c = binary->right->dynCast<Const>()) {
-            seek(binary->left, mul * Pow2(c->value.geti32()));
+            seek(binary->left, mul * Pow2(Bits::getEffectiveShifts(c)));
             return;
           }
         } else if (binary->op == MulInt32) {
@@ -836,7 +836,7 @@ struct OptimizeInstructions : public WalkerPass<PostWalker<OptimizeInstructions,
           }
         } else if (curr->op == ShlInt32) {
           // shifting a 0 is a 0, unless the shift has side effects
-          if (left && left->value.geti32() == 0 && !EffectAnalyzer(passOptions, curr->right).hasSideEffects()) {
+          if (left && Bits::getEffectiveShifts(left) == 0 && !EffectAnalyzer(passOptions, curr->right).hasSideEffects()) {
             replaceCurrent(left);
             return;
           }

test/passes/optimize-instructions.txt

@@ -2061,4 +2061,19 @@
    (i32.const 9)
   )
  )
+ (func $mix-shifts (type $2) (result i32)
+  (i32.shr_s
+   (i32.shl
+    (i32.const 23)
+    (i32.const -61)
+   )
+   (i32.const 168)
+  )
+ )
+ (func $actually-no-shifts (type $2) (result i32)
+  (i32.const 33)
+ )
+ (func $less-shifts-than-it-seems (type $3) (param $x i32) (result i32)
+  (i32.const 4800)
+ )
 )

test/passes/optimize-instructions.wast

@@ -2496,4 +2496,34 @@
     (i32.const 4098) ;; 2 bits effectively
    )
   )
+  (func $mix-shifts (result i32)
+    (i32.shr_s
+     (i32.shl
+      (i32.const 23)
+      (i32.const -61)
+     )
+     (i32.const 168)
+    )
+  )
+  (func $actually-no-shifts (result i32)
+    (i32.add
+      (i32.shl
+        (i32.const 23)
+        (i32.const 32) ;; really 0
+      )
+      (i32.const 10)
+    )
+  )
+  (func $less-shifts-than-it-seems (param $x i32) (result i32)
+    (i32.add
+      (i32.shl
+        (i32.const 200)
+        (i32.const 36) ;; really 4
+      )
+      (i32.shl
+        (i32.const 100)
+        (i32.const 4)
+      )
+    )
+  )
 )