port detectSign from emscripten asm optimizer, and use it

5 files changed, 69 insertions, 3 deletions

diff --git a/src/asm2wasm.h b/src/asm2wasm.h
index 92ef589d2..e44d2b5b1 100644
--- a/src/asm2wasm.h
+++ b/src/asm2wasm.h
@@ -251,9 +251,8 @@ private:
     return asmToWasmType(detectAsmType(ast, data));
   }
 
-  bool isUnsignedCoercion(Ref ast) { // TODO: use detectSign?
-    if (ast[0] == BINARY && ast[1] == TRSHIFT) return true;
-    return false;
+  bool isUnsignedCoercion(Ref ast) {
+    return detectSign(ast) == ASM_UNSIGNED;
   }
 
   // an asm.js binary op can either be a binary or a relational in wasm
diff --git a/src/emscripten-optimizer/optimizer-shared.cpp b/src/emscripten-optimizer/optimizer-shared.cpp
index 1c36efc62..054716b14 100644
--- a/src/emscripten-optimizer/optimizer-shared.cpp
+++ b/src/emscripten-optimizer/optimizer-shared.cpp
@@ -123,3 +123,41 @@ AsmType detectType(Ref node, AsmData *asmData, bool inVarDef) {
   return ASM_NONE;
 }
 
+AsmSign detectSign(Ref node) {
+  IString type = node[0]->getIString();
+  if (type == BINARY) {
+    IString op = node[1]->getIString();
+    switch (op.str[0]) {
+      case '>': {
+        if (op == TRSHIFT) return ASM_UNSIGNED;
+        // fallthrough
+      }
+      case '|': case '&': case '^': case '<': case '=': case '!': return ASM_SIGNED;
+      case '+': case '-': return ASM_FLEXIBLE;
+      case '*': case '/': return ASM_NONSIGNED; // without a coercion, these are double
+      default: abort();
+    }
+  } else if (type == UNARY_PREFIX) {
+    IString op = node[1]->getIString();
+    switch (op.str[0]) {
+      case '-': return ASM_FLEXIBLE;
+      case '+': return ASM_NONSIGNED; // XXX double
+      case '~': return ASM_SIGNED;
+      default: abort();
+    }
+  } else if (type == NUM) {
+    double value = node[1]->getNumber();
+    if (value < 0) return ASM_SIGNED;
+    if (value > uint32_t(-1) || fmod(value, 1) != 0) return ASM_NONSIGNED;
+    if (value == int32_t(value)) return ASM_FLEXIBLE;
+    return ASM_UNSIGNED;
+  } else if (type == NAME) {
+    return ASM_FLEXIBLE;
+  } else if (type == CONDITIONAL) {
+    return detectSign(node[2]);
+  } else if (type == CALL) {
+    if (node[1][0] == NAME && node[1][1] == MATH_FROUND) return ASM_NONSIGNED;
+  }
+  abort();
+}
+
diff --git a/src/emscripten-optimizer/optimizer.h b/src/emscripten-optimizer/optimizer.h
index 5edcaad87..fe1c18770 100644
--- a/src/emscripten-optimizer/optimizer.h
+++ b/src/emscripten-optimizer/optimizer.h
@@ -123,5 +123,14 @@ struct HeapInfo {
 
 HeapInfo parseHeap(const char *name);
 
+enum AsmSign {
+  ASM_FLEXIBLE = 0, // small constants can be signed or unsigned, variables are also flexible
+  ASM_SIGNED = 1,
+  ASM_UNSIGNED = 2,
+  ASM_NONSIGNED = 3,
+};
+
+extern AsmSign detectSign(cashew::Ref node);
+
 #endif // __optimizer_h__
 
diff --git a/test/unit.asm.js b/test/unit.asm.js
index 686535077..77e2c5585 100644
--- a/test/unit.asm.js
+++ b/test/unit.asm.js
@@ -59,6 +59,11 @@ function () {
   function frem() {
     return +(5.5 % 1.2);
   }
+  function big_uint_div_u() {
+    var x = 0;
+    x = (4294967295 / 2)&-1;
+    return x | 0;
+  }
 
   function z() {
   }
diff --git a/test/unit.wast b/test/unit.wast
index 34f8a9d50..170236efc 100644
--- a/test/unit.wast
+++ b/test/unit.wast
@@ -217,6 +217,21 @@
       (f64.const 1.2)
     )
   )
+  (func $big_uint_div_u (result i32)
+    (local $x i32)
+    (block $topmost
+      (set_local $x
+        (i32.and
+          (i32.div_u
+            (i32.const -2147483648)
+            (i32.const 2)
+          )
+          (i32.const -1)
+        )
+      )
+      (get_local $x)
+    )
+  )
   (func $z
     (nop)
   )