fix optimizing two shifts into one; if the number of effective shifts overflows, it is not vali to just add them

2 files changed, 71 insertions, 4 deletions

diff --git a/test/passes/optimize-instructions.txt b/test/passes/optimize-instructions.txt
index f7948860c..e376d97d9 100644
--- a/test/passes/optimize-instructions.txt
+++ b/test/passes/optimize-instructions.txt
@@ -6,6 +6,7 @@
  (type $4 (func (param i32 i32)))
  (type $5 (func (param i32)))
  (type $6 (func (param i32 i32) (result i32)))
+ (type $7 (func (param i64) (result i64)))
  (memory $0 0)
  (export "load-off-2" (func $load-off-2))
  (func $f (type $0) (param $i1 i32) (param $i2 i64)
@@ -734,7 +735,7 @@
    (i32.shr_s
     (i32.shl
      (i32.const 32)
-     (i32.const 59)
+     (i32.const 27)
     )
     (i32.const 24)
    )
@@ -1083,19 +1084,19 @@
   (drop
    (i32.shl
     (get_local $0)
-    (i32.const 211)
+    (i32.const 19)
    )
   )
   (drop
    (i32.shr_s
     (get_local $0)
-    (i32.const 211)
+    (i32.const 19)
    )
   )
   (drop
    (i32.shr_u
     (get_local $0)
-    (i32.const 211)
+    (i32.const 19)
    )
   )
   (drop
@@ -2024,4 +2025,34 @@
    (i32.const 255)
   )
  )
+ (func $shifts-square-overflow (type $3) (param $x i32) (result i32)
+  (i32.shr_u
+   (i32.shr_u
+    (get_local $x)
+    (i32.const 65535)
+   )
+   (i32.const 32767)
+  )
+ )
+ (func $shifts-square-no-overflow-small (type $3) (param $x i32) (result i32)
+  (i32.shr_u
+   (get_local $x)
+   (i32.const 9)
+  )
+ )
+ (func $shifts-square-overflow-64 (type $7) (param $x i64) (result i64)
+  (i64.shr_u
+   (i64.shr_u
+    (get_local $x)
+    (i64.const 65535)
+   )
+   (i64.const 64767)
+  )
+ )
+ (func $shifts-square-no-overflow-small-64 (type $7) (param $x i64) (result i64)
+  (i64.shr_u
+   (get_local $x)
+   (i64.const 9)
+  )
+ )
 )
diff --git a/test/passes/optimize-instructions.wast b/test/passes/optimize-instructions.wast
index 107451b87..7e07e8aee 100644
--- a/test/passes/optimize-instructions.wast
+++ b/test/passes/optimize-instructions.wast
@@ -2451,4 +2451,40 @@
     (i32.const 255)
    )
   )
+  (func $shifts-square-overflow (param $x i32) (result i32)
+   (i32.shr_u
+    (i32.shr_u
+     (get_local $x)
+     (i32.const 65535) ;; 31 bits effectively
+    )
+    (i32.const 32767) ;; also 31 bits, so two shifts that force the value into nothing for sure
+   )
+  )
+  (func $shifts-square-no-overflow-small (param $x i32) (result i32)
+   (i32.shr_u
+    (i32.shr_u
+     (get_local $x)
+     (i32.const 1031) ;; 7 bits effectively
+    )
+    (i32.const 4098) ;; 2 bits effectively
+   )
+  )
+  (func $shifts-square-overflow-64 (param $x i64) (result i64)
+   (i64.shr_u
+    (i64.shr_u
+     (get_local $x)
+     (i64.const 65535) ;; 63 bits effectively
+    )
+    (i64.const 64767) ;; also 63 bits, so two shifts that force the value into nothing for sure
+   )
+  )
+  (func $shifts-square-no-overflow-small-64 (param $x i64) (result i64)
+   (i64.shr_u
+    (i64.shr_u
+     (get_local $x)
+     (i64.const 1031) ;; 7 bits effectively
+    )
+    (i64.const 4098) ;; 2 bits effectively
+   )
+  )
 )