Reject non-naturally aligned loads and stores.

llvm/lib/YkIR/YkIRWriter.cpp

@@ -886,23 +886,21 @@ class YkIRWriter {
     //  - loads from exotic address spaces
     //  - potentially misaligned loads
     //
-    // FIXME: About misaligned loads, when a load is aligned `N`, this is a hard
-    // guarantee to the code generator that at runtime, the pointer is aligned
-    // to N bytes. The codegen uses this to decide whether or not to split the
-    // operation into multiple loads (in order to avoid a memory access
-    // straddling an alignment boundary on a CPU that disallows such things).
-    //
-    // For now we let through only loads with an alignment greater-than or
-    // equal-to the size of the type of the data being loaded. Such cases are
-    // trivially safe, since the codegen will never have to face an unaligned
-    // load for these.
+    // FIXME: About the `align` keyword for load instructions: `align N` is a
+    // hard guarantee to the code generator that at runtime, the pointer is
+    // aligned to N bytes. The codegen uses this to decide whether or not to
+    // split the operation into multiple loads (in order to avoid a memory
+    // access straddling an alignment boundary on a CPU that disallows such
+    // things). Since many parts of the JIT assume that an object's memory is
+    // naturally aligned, for now we let through only loads with natural
+    // alignment.
     //
     // Eventually we will have to encode the alignment of the load into our IR
     // and have the trace code generator split up the loads where necessary.
     // The same will have to be done for store instructions.
     if ((I->getOrdering() != AtomicOrdering::NotAtomic) ||
         (I->getPointerAddressSpace() != 0) ||
-        (I->getAlign() < DL.getTypeAllocSize(I->getType()))) {
+        (I->getAlign() != DL.getTypeAllocSize(I->getType()))) {
       serialiseUnimplementedInstruction(I, FLCtxt, BBIdx, InstIdx);
       return;
     }
@@ -925,13 +923,12 @@ class YkIRWriter {
     // We don't yet support:
     //  - atomic store
     //  - stores into exotic address spaces
-    //  - potentially misaligned stores
+    //  - non-natural alignments
     //
-    // See the comment in `serialiseLoadInst()` for context on misaligned memory
-    // accesses.
+    // See the comment in `serialiseLoadInst()` for context on alignment.
     if ((I->getOrdering() != AtomicOrdering::NotAtomic) ||
         (I->getPointerAddressSpace() != 0) ||
-        (I->getAlign() <
+        (I->getAlign() !=
          DL.getTypeAllocSize(I->getValueOperand()->getType()))) {
       serialiseUnimplementedInstruction(I, FLCtxt, BBIdx, InstIdx);
       return;