codegen: ensure safepoint functions can read the pgcstack (#58804)

This needs to be readOnly over all memory, since GC could read anything
(especially pgcstack), and which is not just argmem:read, but also the
pointer accessed from argmem that is read from.

Fix #58801

Note that this is thought not to be a problem for CleanupWriteBarriers,
since while that does read the previously-inaccessibleMemOnly state,
these functions are not marked nosync, so as long as the global state
can be read, it also must be assumed that it might observe another
thread has written to any global state.

Author: vtjnash

src/codegen.cpp

@@ -641,7 +641,7 @@ static AttributeList get_attrs_box_float(LLVMContext &C, unsigned nbytes)
     auto FnAttrs = AttrBuilder(C);
     FnAttrs.addAttribute(Attribute::WillReturn);
     FnAttrs.addAttribute(Attribute::NoUnwind);
-    FnAttrs.addMemoryAttr(MemoryEffects::inaccessibleMemOnly());
+    FnAttrs.addMemoryAttr(MemoryEffects::inaccessibleMemOnly() | MemoryEffects::readOnly());
     auto RetAttrs = AttrBuilder(C);
     RetAttrs.addAttribute(Attribute::NonNull);
     RetAttrs.addDereferenceableAttr(nbytes);
@@ -657,7 +657,7 @@ static AttributeList get_attrs_box_sext(LLVMContext &C, unsigned nbytes)
     auto FnAttrs = AttrBuilder(C);
     FnAttrs.addAttribute(Attribute::WillReturn);
     FnAttrs.addAttribute(Attribute::NoUnwind);
-    FnAttrs.addMemoryAttr(MemoryEffects::inaccessibleMemOnly());
+    FnAttrs.addMemoryAttr(MemoryEffects::inaccessibleMemOnly() | MemoryEffects::readOnly());
     auto RetAttrs = AttrBuilder(C);
     RetAttrs.addAttribute(Attribute::NonNull);
     RetAttrs.addAttribute(Attribute::getWithDereferenceableBytes(C, nbytes));
@@ -674,7 +674,7 @@ static AttributeList get_attrs_box_zext(LLVMContext &C, unsigned nbytes)
     auto FnAttrs = AttrBuilder(C);
     FnAttrs.addAttribute(Attribute::WillReturn);
     FnAttrs.addAttribute(Attribute::NoUnwind);
-    FnAttrs.addMemoryAttr(MemoryEffects::inaccessibleMemOnly());
+    FnAttrs.addMemoryAttr(MemoryEffects::inaccessibleMemOnly() | MemoryEffects::readOnly());
     auto RetAttrs = AttrBuilder(C);
     RetAttrs.addAttribute(Attribute::NonNull);
     RetAttrs.addDereferenceableAttr(nbytes);
@@ -1125,7 +1125,7 @@ static const auto jl_alloc_obj_func = new JuliaFunction<TypeFnContextAndSizeT>{
         auto FnAttrs = AttrBuilder(C);
         FnAttrs.addAllocSizeAttr(1, None); // returns %1 bytes
         FnAttrs.addAllocKindAttr(AllocFnKind::Alloc);
-        FnAttrs.addMemoryAttr(MemoryEffects::argMemOnly(ModRefInfo::Ref) | MemoryEffects::inaccessibleMemOnly(ModRefInfo::ModRef));
+        FnAttrs.addMemoryAttr(MemoryEffects::argMemOnly(ModRefInfo::Ref) | MemoryEffects::inaccessibleMemOnly());
         FnAttrs.addAttribute(Attribute::WillReturn);
         FnAttrs.addAttribute(Attribute::NoUnwind);
         auto RetAttrs = AttrBuilder(C);
@@ -1149,7 +1149,7 @@ static const auto jl_alloc_genericmemory_unchecked_func = new JuliaFunction<Type
     [](LLVMContext &C) {
         auto FnAttrs = AttrBuilder(C);
         FnAttrs.addAllocKindAttr(AllocFnKind::Alloc);
-        FnAttrs.addMemoryAttr(MemoryEffects::argMemOnly(ModRefInfo::Ref) | MemoryEffects::inaccessibleMemOnly(ModRefInfo::ModRef));
+        FnAttrs.addMemoryAttr(MemoryEffects::argMemOnly(ModRefInfo::Ref) | MemoryEffects::inaccessibleMemOnly());
         FnAttrs.addAttribute(Attribute::WillReturn);
         FnAttrs.addAttribute(Attribute::NoUnwind);
         auto RetAttrs = AttrBuilder(C);
@@ -1394,7 +1394,7 @@ static const auto jl_allocgenericmemory = new JuliaFunction<TypeFnContextAndSize
         [](LLVMContext &C) {
             AttrBuilder FnAttrs(C);
             AttrBuilder RetAttrs(C);
-            FnAttrs.addMemoryAttr(MemoryEffects::inaccessibleMemOnly(ModRefInfo::ModRef) | MemoryEffects::argMemOnly(ModRefInfo::Ref));
+            FnAttrs.addMemoryAttr(MemoryEffects::inaccessibleMemOnly() | MemoryEffects::readOnly());
             FnAttrs.addAttribute(Attribute::WillReturn);
             RetAttrs.addAlignmentAttr(Align(16));
             RetAttrs.addAttribute(Attribute::NonNull);
@@ -1438,7 +1438,7 @@ static const auto jldnd_func = new JuliaFunction<>{
     },
     [](LLVMContext &C) {
         AttrBuilder FnAttrs(C);
-        FnAttrs.addMemoryAttr(MemoryEffects::inaccessibleMemOnly());
+        FnAttrs.addMemoryAttr(MemoryEffects::inaccessibleMemOnly() | MemoryEffects::readOnly());
         FnAttrs.addAttribute(Attribute::WillReturn);
         FnAttrs.addAttribute(Attribute::NoUnwind);
         return AttributeList::get(C,