emit safe calls for i32 div/rem when in precise mode in asm2wasm, as they can trap (#637)

4 files changed, 45 insertions, 0 deletions

diff --git a/src/asm2wasm.h b/src/asm2wasm.h
index 994342b4e..c0f13ff8f 100644
--- a/src/asm2wasm.h
+++ b/src/asm2wasm.h
@@ -1075,6 +1075,31 @@ Function* Asm2WasmBuilder::processFunction(Ref ast) {
           wasm.addImport(import);
         }
         return call;
+      } else if (!imprecise && (ret->op == BinaryOp::RemSInt32 || ret->op == BinaryOp::RemUInt32 ||
+                                ret->op == BinaryOp::DivSInt32 || ret->op == BinaryOp::DivUInt32)) {
+        // we are precise, and the wasm operation might trap if done over 0, so generate a safe call
+        CallImport *call = allocator.alloc<CallImport>();
+        switch (ret->op) {
+          case BinaryOp::RemSInt32: call->target = I32S_REM; break;
+          case BinaryOp::RemUInt32: call->target = I32U_REM; break;
+          case BinaryOp::DivSInt32: call->target = I32S_DIV; break;
+          case BinaryOp::DivUInt32: call->target = I32U_DIV; break;
+          default: WASM_UNREACHABLE();
+        }
+        call->operands.push_back(ret->left);
+        call->operands.push_back(ret->right);
+        call->type = i32;
+        static std::set<Name> addedImport;
+        if (addedImport.count(call->target) == 0) {
+          addedImport.insert(call->target);
+          auto import = new Import;
+          import->name = call->target;
+          import->module = ASM2WASM;
+          import->base = call->target;
+          import->type = ensureFunctionType("iii", &wasm);
+          wasm.addImport(import);
+        }
+        return call;
       }
       return ret;
     } else if (what == NUM) {
diff --git a/src/asmjs/shared-constants.cpp b/src/asmjs/shared-constants.cpp
index b2321a209..e30fd939c 100644
--- a/src/asmjs/shared-constants.cpp
+++ b/src/asmjs/shared-constants.cpp
@@ -40,6 +40,10 @@ cashew::IString GLOBAL("global"),
                 ASM2WASM("asm2wasm"),
                 F64_REM("f64-rem"),
                 F64_TO_INT("f64-to-int"),
+                I32S_DIV("i32s-div"),
+                I32U_DIV("i32u-div"),
+                I32S_REM("i32s-rem"),
+                I32U_REM("i32u-rem"),
                 GLOBAL_MATH("global.Math"),
                 ABS("abs"),
                 FLOOR("floor"),
diff --git a/src/asmjs/shared-constants.h b/src/asmjs/shared-constants.h
index fb32340ab..e0c627511 100644
--- a/src/asmjs/shared-constants.h
+++ b/src/asmjs/shared-constants.h
@@ -43,6 +43,10 @@ extern cashew::IString GLOBAL,
                 ASM2WASM,
                 F64_REM,
                 F64_TO_INT,
+                I32S_DIV,
+                I32U_DIV,
+                I32S_REM,
+                I32U_REM,
                 GLOBAL_MATH,
                 ABS,
                 FLOOR,
diff --git a/src/js/wasm.js-post.js b/src/js/wasm.js-post.js
index 6d73981f1..ae42ef175 100644
--- a/src/js/wasm.js-post.js
+++ b/src/js/wasm.js-post.js
@@ -45,6 +45,18 @@ function integrateWasmJS(Module) {
     "f64-to-int": function(x) {
       return x | 0;
     },
+    "i32s-div": function(x, y) {
+      return ((x | 0) / (y | 0)) | 0;
+    },
+    "i32u-div": function(x, y) {
+      return ((x >>> 0) / (y >>> 0)) >>> 0;
+    },
+    "i32s-rem": function(x, y) {
+      return ((x | 0) % (y | 0)) | 0;
+    },
+    "i32u-rem": function(x, y) {
+      return ((x >>> 0) % (y >>> 0)) >>> 0;
+    },
     "debugger": function() {
       debugger;
     },