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

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

3 files changed, 61 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))) &&
diff --git a/test/passes/optimize-instructions_all-features.txt b/test/passes/optimize-instructions_all-features.txt
index 80bd7a89d..15a38f267 100644
--- a/test/passes/optimize-instructions_all-features.txt
+++ b/test/passes/optimize-instructions_all-features.txt
@@ -19,6 +19,7 @@
  (type $f32_=>_none (func (param f32)))
  (type $f32_f64_=>_none (func (param f32 f64)))
  (type $f64_=>_none (func (param f64)))
+ (type $f64_f32_=>_none (func (param f64 f32)))
  (type $f64_f64_f32_f32_=>_none (func (param f64 f64 f32 f32)))
  (type $none_=>_f64 (func (result f64)))
  (memory $0 0)
@@ -4597,6 +4598,34 @@
    )
   )
  )
+ (func $optimize-float-mul-by-two (param $0 f64) (param $1 f32)
+  (drop
+   (f64.add
+    (local.get $0)
+    (local.get $0)
+   )
+  )
+  (drop
+   (f32.add
+    (local.get $1)
+    (local.get $1)
+   )
+  )
+  (drop
+   (f64.mul
+    (call $tee-with-unreachable-value)
+    (f64.const 2)
+   )
+  )
+  (drop
+   (f64.mul
+    (f64.neg
+     (local.get $0)
+    )
+    (f64.const 2)
+   )
+  )
+ )
  (func $duplicate-elimination (param $x i32) (param $y i32) (param $z i32) (param $w f64)
   (drop
    (f64.abs
diff --git a/test/passes/optimize-instructions_all-features.wast b/test/passes/optimize-instructions_all-features.wast
index c3a6aaf59..c9f071727 100644
--- a/test/passes/optimize-instructions_all-features.wast
+++ b/test/passes/optimize-instructions_all-features.wast
@@ -5069,6 +5069,25 @@
       (i32.const -7) ;; skip
     ))
   )
+  (func $optimize-float-mul-by-two (param $0 f64) (param $1 f32)
+    (drop (f64.mul
+      (local.get $0)
+      (f64.const 2)
+    ))
+    (drop (f32.mul
+      (local.get $1)
+      (f32.const 2)
+    ))
+
+    (drop (f64.mul
+      (call $tee-with-unreachable-value) ;; side effect
+      (f64.const 2)
+    ))
+    (drop (f64.mul
+      (f64.neg (local.get $0)) ;; complex expression
+      (f64.const 2)
+    ))
+  )
   (func $duplicate-elimination (param $x i32) (param $y i32) (param $z i32) (param $w f64)
     ;; unary
     (drop (f64.abs (f64.abs (local.get $w))))