[WebAssembly] Implement unaligned loads and stores.

Differential Revision: http://reviews.llvm.org/D16534

llvm-svn: 258779

1 files changed, 14 insertions, 0 deletions

diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp
index e9933b09298..3906b9d5387 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp
@@ -285,6 +285,20 @@ bool WebAssemblyTargetLowering::isLegalAddressingMode(const DataLayout &DL,
   return true;
 }
 
+bool WebAssemblyTargetLowering::allowsMisalignedMemoryAccesses(
+    EVT /*VT*/, unsigned /*AddrSpace*/, unsigned /*Align*/,
+    bool *Fast) const {
+  // WebAssembly supports unaligned accesses, though it should be declared
+  // with the p2align attribute on loads and stores which do so, and there
+  // may be a performance impact. We tell LLVM they're "fast" because
+  // for the kinds of things that LLVM uses this for (merging agacent stores
+  // of constants, etc.), WebAssembly implementations will either want the
+  // unaligned access or they'll split anyway.
+  if (Fast)
+    *Fast = true;
+  return true;
+}
+
 //===----------------------------------------------------------------------===//
 // WebAssembly Lowering private implementation.
 //===----------------------------------------------------------------------===//