1 files changed, 107 insertions, 0 deletions
diff --git a/src/ir/bits.h b/src/ir/bits.h
new file mode 100644
index 000000000..4196b74c1
--- /dev/null
+++ b/src/ir/bits.h
@@ -0,0 +1,107 @@
+/*
+ * Copyright 2017 WebAssembly Community Group participants
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef wasm_ir_bits_h
+#define wasm_ir_bits_h
+
+#include "support/bits.h"
+#include "wasm-builder.h"
+#include "ir/literal-utils.h"
+
+namespace wasm {
+
+struct Bits {
+  // get a mask to keep only the low # of bits
+  static int32_t lowBitMask(int32_t bits) {
+    uint32_t ret = -1;
+    if (bits >= 32) return ret;
+    return ret >> (32 - bits);
+  }
+
+  // checks if the input is a mask of lower bits, i.e., all 1s up to some high bit, and all zeros
+  // from there. returns the number of masked bits, or 0 if this is not such a mask
+  static uint32_t getMaskedBits(uint32_t mask) {
+    if (mask == uint32_t(-1)) return 32; // all the bits
+    if (mask == 0) return 0; // trivially not a mask
+    // otherwise, see if adding one turns this into a 1-bit thing, 00011111 + 1 => 00100000
+    if (PopCount(mask + 1) != 1) return 0;
+    // this is indeed a mask
+    return 32 - CountLeadingZeroes(mask);
+  }
+
+  // gets the number of effective shifts a shift operation does. In
+  // wasm, only 5 bits matter for 32-bit shifts, and 6 for 64.
+  static Index getEffectiveShifts(Index amount, WasmType type) {
+    if (type == i32) {
+      return amount & 31;
+    } else if (type == i64) {
+      return amount & 63;
+    }
+    WASM_UNREACHABLE();
+  }
+
+  static Index getEffectiveShifts(Expression* expr) {
+    auto* amount = expr->cast<Const>();
+    if (amount->type == i32) {
+      return getEffectiveShifts(amount->value.geti32(), i32);
+    } else if (amount->type == i64) {
+      return getEffectiveShifts(amount->value.geti64(), i64);
+    }
+    WASM_UNREACHABLE();
+  }
+
+  static Expression* makeSignExt(Expression* value, Index bytes, Module& wasm) {
+    if (value->type == i32) {
+      if (bytes == 1 || bytes == 2) {
+        auto shifts = bytes == 1 ? 24 : 16;
+        Builder builder(wasm);
+        return builder.makeBinary(
+          ShrSInt32,
+          builder.makeBinary(
+            ShlInt32,
+            value,
+            LiteralUtils::makeFromInt32(shifts, i32, wasm)
+          ),
+          LiteralUtils::makeFromInt32(shifts, i32, wasm)
+        );
+      }
+      assert(bytes == 4);
+      return value; // nothing to do
+    } else {
+      assert(value->type == i64);
+      if (bytes == 1 || bytes == 2 || bytes == 4) {
+        auto shifts = bytes == 1 ? 56 : (bytes == 2 ? 48 : 32);
+        Builder builder(wasm);
+        return builder.makeBinary(
+          ShrSInt64,
+          builder.makeBinary(
+            ShlInt64,
+            value,
+            LiteralUtils::makeFromInt32(shifts, i64, wasm)
+          ),
+          LiteralUtils::makeFromInt32(shifts, i64, wasm)
+        );
+      }
+      assert(bytes == 8);
+      return value; // nothing to do
+    }
+  }
+};
+
+} // namespace wasm
+
+#endif // wasm_ir_bits_h
+