Fix comparisons of sign-extends to weird constants (#956)

* fix eq/ne of sign-ext with a constant, when the constant can never be equal to it as it has the effective sign bit but not the upper bits above it set, which the sign-ext would emit

2 files changed, 217 insertions, 3 deletions

diff --git a/test/passes/optimize-instructions.txt b/test/passes/optimize-instructions.txt
index 41d45d57f..03edc6e4c 100644
--- a/test/passes/optimize-instructions.txt
+++ b/test/passes/optimize-instructions.txt
@@ -541,7 +541,16 @@
      (get_local $0)
      (i32.const 255)
     )
-    (i32.const 255)
+    (i32.const -2147483648)
+   )
+  )
+  (drop
+   (i32.eq
+    (i32.and
+     (get_local $0)
+     (i32.const 255)
+    )
+    (i32.const 107)
    )
   )
   (drop
@@ -1103,7 +1112,25 @@
      (get_local $0)
      (i32.const 255)
     )
-    (i32.const 232)
+    (i32.const -2147483648)
+   )
+  )
+  (drop
+   (i32.ne
+    (i32.and
+     (get_local $0)
+     (i32.const 255)
+    )
+    (i32.const -2147483648)
+   )
+  )
+  (drop
+   (i32.ne
+    (i32.and
+     (get_local $0)
+     (i32.const 255)
+    )
+    (i32.const 107)
    )
   )
   (drop
@@ -1790,4 +1817,69 @@
    )
   )
  )
+ (func $fuzz-comp-impossible (type $5) (param $x i32)
+  (drop
+   (i32.eq
+    (i32.and
+     (get_local $x)
+     (i32.const 65535)
+    )
+    (i32.const -2147483648)
+   )
+  )
+  (drop
+   (i32.eq
+    (i32.and
+     (get_local $x)
+     (i32.const 255)
+    )
+    (i32.const -2147483648)
+   )
+  )
+  (drop
+   (i32.eq
+    (i32.and
+     (get_local $x)
+     (i32.const 255)
+    )
+    (i32.const 127)
+   )
+  )
+  (drop
+   (i32.eq
+    (i32.and
+     (get_local $x)
+     (i32.const 255)
+    )
+    (i32.const -2147483648)
+   )
+  )
+  (drop
+   (i32.eq
+    (i32.and
+     (get_local $x)
+     (i32.const 255)
+    )
+    (i32.const -2147483648)
+   )
+  )
+  (drop
+   (i32.eq
+    (i32.and
+     (get_local $x)
+     (i32.const 255)
+    )
+    (i32.const -2147483648)
+   )
+  )
+  (drop
+   (i32.eq
+    (i32.and
+     (get_local $x)
+     (i32.const 255)
+    )
+    (i32.const 252)
+   )
+  )
+ )
 )
diff --git a/test/passes/optimize-instructions.wast b/test/passes/optimize-instructions.wast
index 8ef6f67a5..eccbf1268 100644
--- a/test/passes/optimize-instructions.wast
+++ b/test/passes/optimize-instructions.wast
@@ -491,7 +491,19 @@
           )
           (i32.const 24)
         )
-        (i32.const 32767) ;; non-zero and bigger than the mask
+        (i32.const 32767) ;; non-zero and bigger than the mask, with sign bit
+      )
+    )
+    (drop
+      (i32.eq
+        (i32.shr_s
+          (i32.shl
+            (get_local $0)
+            (i32.const 24)
+          )
+          (i32.const 24)
+        )
+        (i32.const -149) ;; non-zero and bigger than the mask, without sign bit
       )
     )
     ;; eq of two sign-ext, can both be a zext
@@ -1370,6 +1382,30 @@
           )
           (i32.const 24)
         )
+        (i32.const 64872) ;; no sign bit
+      )
+    )
+    (drop
+      (i32.ne
+        (i32.shr_s
+          (i32.shl
+            (get_local $0)
+            (i32.const 24)
+          )
+          (i32.const 24)
+        )
+        (i32.const -149) ;; no sign bit, not all ones
+      )
+    )
+    (drop
+      (i32.ne
+        (i32.shr_s
+          (i32.shl
+            (get_local $0)
+            (i32.const 24)
+          )
+          (i32.const 24)
+        )
         (i32.const 111)
       )
     )
@@ -2181,4 +2217,90 @@
       )
     )
   )
+  (func $fuzz-comp-impossible (param $x i32)
+    (drop
+      (i32.eq
+        (i32.shr_s
+          (i32.shl
+            (get_local $x)
+            (i32.const 16)
+          )
+          (i32.const 16)
+        )
+        (i32.const 65535) ;; impossible to be equal, the effective sign bit is set, but not the higher bits, which the sign-ext will set on the non-const value
+      )
+    )
+    (drop
+      (i32.eq
+        (i32.shr_s
+          (i32.shl
+            (get_local $x)
+            (i32.const 24)
+          )
+          (i32.const 24)
+        )
+        (i32.const 255)
+      )
+    )
+    (drop
+      (i32.eq
+        (i32.shr_s
+          (i32.shl
+            (get_local $x)
+            (i32.const 24)
+          )
+          (i32.const 24)
+        )
+        (i32.const 127) ;; safe
+      )
+    )
+    (drop
+      (i32.eq
+        (i32.shr_s
+          (i32.shl
+            (get_local $x)
+            (i32.const 24)
+          )
+          (i32.const 24)
+        )
+        (i32.const 128) ;; unsafe again
+      )
+    )
+    (drop
+      (i32.eq
+        (i32.shr_s
+          (i32.shl
+            (get_local $x)
+            (i32.const 24)
+          )
+          (i32.const 24)
+        )
+        (i32.const 4223) ;; more big bits, so sign bit though
+      )
+    )
+    (drop
+      (i32.eq
+        (i32.shr_s
+          (i32.shl
+            (get_local $x)
+            (i32.const 24)
+          )
+          (i32.const 24)
+        )
+        (i32.const 4224) ;; more big bits
+      )
+    )
+    (drop
+      (i32.eq
+        (i32.shr_s
+          (i32.shl
+            (get_local $x)
+            (i32.const 24)
+          )
+          (i32.const 24)
+        )
+        (i32.const -4) ;; safe even with more big bits, as they are all 1s
+      )
+    )
+  )
 )