WARN_UNALIGNED option for fastcomp

3 files changed, 26 insertions, 0 deletions

diff --git a/emscripten.py b/emscripten.py
index b75df587..c96c56a0 100755
--- a/emscripten.py
+++ b/emscripten.py
@@ -742,6 +742,8 @@ def emscript_fast(infile, settings, outfile, libraries=[], compiler_engine=None,
   backend_args = [backend_compiler, infile, '-march=js', '-filetype=asm', '-o', temp_js]
   if settings['PRECISE_F32']:
     backend_args += ['-emscripten-precise-f32']
+  if settings['WARN_UNALIGNED']:
+    backend_args += ['-emscripten-warn-unaligned']
   if DEBUG:
     logging.debug('emscript: llvm backend: ' + ' '.join(backend_args))
     t = time.time()
diff --git a/src/settings.js b/src/settings.js
index 1cfb4030..8f3ef70b 100644
--- a/src/settings.js
+++ b/src/settings.js
@@ -104,6 +104,9 @@ var FORCE_ALIGNED_MEMORY = 0; // If enabled, assumes all reads and writes are fu
                               // for ways to help find places in your code where unaligned reads/writes are done -
                               // you might be able to refactor your codebase to prevent them, which leads to
                               // smaller and faster code, or even the option to turn this flag on.
+var WARN_UNALIGNED = 1; // Warn at compile time about instructions that LLVM tells us are not fully aligned.
+                        // This is useful to find places in your code where you might refactor to ensure proper
+                        // alignment. (this option is fastcomp-only)
 var PRECISE_I64_MATH = 1; // If enabled, i64 addition etc. is emulated - which is slow but precise. If disabled,
                           // we use the 'double trick' which is fast but incurs rounding at high values.
                           // Note that we do not catch 32-bit multiplication by default (which must be done in
diff --git a/tests/test_other.py b/tests/test_other.py
index 47d26416..a6a9c52f 100644
--- a/tests/test_other.py
+++ b/tests/test_other.py
@@ -2353,3 +2353,24 @@ int main() {
     err = Popen([PYTHON, EMCC, 'src.cpp', '-include', 'header.h', '-Xclang', '-print-stats'], stderr=PIPE).communicate()
     assert '*** PCH/Modules Loaded:\nModule: header.h.gch' not in err[1], err[1]
 
+  def test_warn_unaligned(self):
+    if os.environ.get('EMCC_FAST_COMPILER') != '1': return self.skip('need fastcomp')
+    open('src.cpp', 'w').write(r'''
+#include <stdio.h>
+static const double grid[4][2] = {{-3 / 3., -1 / 3.},
+                                  {+1 / 3., -3 / 3.},
+                                  {-1 / 3., +3 / 3.},
+                                  {+3 / 3., +1 / 3.}};
+int main() {
+  for (int i = 0; i < 4; i++)
+    printf("%d:%.2f,%.2f ", i, grid[i][0], grid[i][1]);
+  printf("\n");
+  return 0;
+}
+''')
+    output = Popen([PYTHON, EMCC, 'src.cpp', '-O1', '-s', 'WARN_UNALIGNED=1'], stderr=PIPE).communicate()
+    assert 'emcc: warning: unaligned store' in output[1]
+    output = Popen([PYTHON, EMCC, 'src.cpp', '-s', 'WARN_UNALIGNED=1', '-g'], stderr=PIPE).communicate()
+    assert 'emcc: warning: unaligned store' in output[1]
+    assert '@line 9 "src.cpp"' in output[1]
+