threads: fix semantic error in old Threads.Atomic

(cherry picked from commit aa421ff)

Author: vtjnash

base/atomics.jl

@@ -356,13 +356,13 @@ for typ in atomictypes
     rt = "$lt, $lt*"
     irt = "$ilt, $ilt*"
     @eval getindex(x::Atomic{$typ}) =
-        llvmcall($"""
+        GC.@preserve x llvmcall($"""
                  %ptr = inttoptr i$WORD_SIZE %0 to $lt*
                  %rv = load atomic $rt %ptr acquire, align $(gc_alignment(typ))
                  ret $lt %rv
                  """, $typ, Tuple{Ptr{$typ}}, unsafe_convert(Ptr{$typ}, x))
     @eval setindex!(x::Atomic{$typ}, v::$typ) =
-        llvmcall($"""
+        GC.@preserve x llvmcall($"""
                  %ptr = inttoptr i$WORD_SIZE %0 to $lt*
                  store atomic $lt %1, $lt* %ptr release, align $(gc_alignment(typ))
                  ret void
@@ -371,7 +371,7 @@ for typ in atomictypes
     # Note: atomic_cas! succeeded (i.e. it stored "new") if and only if the result is "cmp"
     if typ <: Integer
         @eval atomic_cas!(x::Atomic{$typ}, cmp::$typ, new::$typ) =
-            llvmcall($"""
+            GC.@preserve x llvmcall($"""
                      %ptr = inttoptr i$WORD_SIZE %0 to $lt*
                      %rs = cmpxchg $lt* %ptr, $lt %1, $lt %2 acq_rel acquire
                      %rv = extractvalue { $lt, i1 } %rs, 0
@@ -380,7 +380,7 @@ for typ in atomictypes
                      unsafe_convert(Ptr{$typ}, x), cmp, new)
     else
         @eval atomic_cas!(x::Atomic{$typ}, cmp::$typ, new::$typ) =
-            llvmcall($"""
+            GC.@preserve x llvmcall($"""
                      %iptr = inttoptr i$WORD_SIZE %0 to $ilt*
                      %icmp = bitcast $lt %1 to $ilt
                      %inew = bitcast $lt %2 to $ilt
@@ -403,15 +403,15 @@ for typ in atomictypes
         if rmwop in arithmetic_ops && !(typ <: ArithmeticTypes) continue end
         if typ <: Integer
             @eval $fn(x::Atomic{$typ}, v::$typ) =
-                llvmcall($"""
+                GC.@preserve x llvmcall($"""
                          %ptr = inttoptr i$WORD_SIZE %0 to $lt*
                          %rv = atomicrmw $rmw $lt* %ptr, $lt %1 acq_rel
                          ret $lt %rv
                          """, $typ, Tuple{Ptr{$typ}, $typ}, unsafe_convert(Ptr{$typ}, x), v)
         else
             rmwop === :xchg || continue
             @eval $fn(x::Atomic{$typ}, v::$typ) =
-                llvmcall($"""
+                GC.@preserve x llvmcall($"""
                          %iptr = inttoptr i$WORD_SIZE %0 to $ilt*
                          %ival = bitcast $lt %1 to $ilt
                          %irv = atomicrmw $rmw $ilt* %iptr, $ilt %ival acq_rel

src/llvm-alloc-opt.cpp

@@ -628,6 +628,21 @@ void Optimizer::checkInst(Instruction *I)
                 use_info.hasunknownmem = true;
             return true;
         }
+        if (isa<AtomicCmpXchgInst>(inst) || isa<AtomicRMWInst>(inst)) {
+            // Only store value count
+            if (use->getOperandNo() != isa<AtomicCmpXchgInst>(inst) ? AtomicCmpXchgInst::getPointerOperandIndex() : AtomicRMWInst::getPointerOperandIndex()) {
+                use_info.escaped = true;
+                return false;
+            }
+            use_info.hasload = true;
+            auto storev = isa<AtomicCmpXchgInst>(inst) ? cast<AtomicCmpXchgInst>(inst)->getNewValOperand() : cast<AtomicRMWInst>(inst)->getValOperand();
+            if (cur.offset == UINT32_MAX || !use_info.addMemOp(inst, use->getOperandNo(),
+                                                               cur.offset, storev->getType(),
+                                                               true, *pass.DL))
+                use_info.hasunknownmem = true;
+            use_info.refload = true;
+            return true;
+        }
         if (isa<AddrSpaceCastInst>(inst) || isa<BitCastInst>(inst)) {
             push_inst(inst);
             return true;
@@ -1331,6 +1346,22 @@ void Optimizer::splitOnStack(CallInst *orig_inst)
             store->eraseFromParent();
             return;
         }
+        else if (isa<AtomicCmpXchgInst>(user) || isa<AtomicRMWInst>(user)) {
+            auto slot_idx = find_slot(offset);
+            auto &slot = slots[slot_idx];
+            assert(slot.offset <= offset && slot.offset + slot.size >= offset);
+            IRBuilder<> builder(user);
+            Value *newptr;
+            if (slot.isref) {
+                assert(slot.offset == offset);
+                newptr = slot.slot;
+            }
+            else {
+                Value *Val = isa<AtomicCmpXchgInst>(user) ? cast<AtomicCmpXchgInst>(user)->getNewValOperand() : cast<AtomicRMWInst>(user)->getValOperand();
+                newptr = slot_gep(slot, offset, Val->getType(), builder);
+            }
+            *use = newptr;
+        }
         else if (auto call = dyn_cast<CallInst>(user)) {
             auto callee = call->getCalledOperand();
             assert(callee); // makes it clear for clang analyser that `callee` is not NULL