Replace x * 2 with x + x for floats (#3016)

But only when doing so doesn't require adding a new local.

1 files changed, 13 insertions, 0 deletions

diff --git a/src/passes/OptimizeInstructions.cpp b/src/passes/OptimizeInstructions.cpp
index b11df3276..89315ab60 100644
--- a/src/passes/OptimizeInstructions.cpp
+++ b/src/passes/OptimizeInstructions.cpp
@@ -1664,6 +1664,19 @@ private:
       }
     }
     {
+      // x * 2.0  ==>  x + x
+      // but we apply this only for simple expressions like
+      // local.get and global.get for avoid using extra local
+      // variable.
+      Expression* x;
+      if (matches(curr, binary(Mul, any(&x), fval(2.0))) &&
+          (x->is<LocalGet>() || x->is<GlobalGet>())) {
+        curr->op = Abstract::getBinary(type, Abstract::Add);
+        curr->right = ExpressionManipulator::copy(x, *getModule());
+        return curr;
+      }
+    }
+    {
       // x + (-0.0)   ==>   x
       double value;
       if (fastMath && matches(curr, binary(Add, any(), fval(&value))) &&