codegen: take gc roots (and alloca alignment) more seriously (#55336)

Due to limitations in the LLVM implementation, we are forced to emit
fairly bad code here. But we need to make sure it is still correct with
respect to GC rooting.

Fixes #54720

src/abi_aarch64.cpp

@@ -16,7 +16,7 @@ struct ABI_AArch64Layout : AbiLayout {
 Type *get_llvm_vectype(jl_datatype_t *dt, LLVMContext &ctx) const
 {
     // Assume jl_is_datatype(dt) && !jl_is_abstracttype(dt)
-    // `!dt->name->mutabl && dt->pointerfree && !dt->haspadding && dt->nfields > 0`
+    // `!dt->name->mutabl && dt->pointerfree && !dt->haspadding && dt->isbitsegal && dt->nfields > 0`
     if (dt->layout == NULL || jl_is_layout_opaque(dt->layout))
         return nullptr;
     size_t nfields = dt->layout->nfields;
@@ -62,7 +62,7 @@ Type *get_llvm_vectype(jl_datatype_t *dt, LLVMContext &ctx) const
 Type *get_llvm_fptype(jl_datatype_t *dt, LLVMContext &ctx) const
 {
     // Assume jl_is_datatype(dt) && !jl_is_abstracttype(dt)
-    // `!dt->name->mutabl && dt->pointerfree && !dt->haspadding && dt->nfields == 0`
+    // `!dt->name->mutabl && dt->pointerfree && !dt->haspadding && dt->isbitsegal && dt->nfields == 0`
     Type *lltype;
     // Check size first since it's cheaper.
     switch (jl_datatype_size(dt)) {
@@ -88,7 +88,7 @@ Type *get_llvm_fptype(jl_datatype_t *dt, LLVMContext &ctx) const
 Type *get_llvm_fp_or_vectype(jl_datatype_t *dt, LLVMContext &ctx) const
 {
     // Assume jl_is_datatype(dt) && !jl_is_abstracttype(dt)
-    if (dt->name->mutabl || dt->layout->npointers || dt->layout->flags.haspadding)
+    if (dt->name->mutabl || dt->layout->npointers || !dt->layout->flags.isbitsegal || dt->layout->flags.haspadding)
         return nullptr;
     return dt->layout->nfields ? get_llvm_vectype(dt, ctx) : get_llvm_fptype(dt, ctx);
 }
@@ -184,7 +184,7 @@ Type *isHFAorHVA(jl_datatype_t *dt, size_t &nele, LLVMContext &ctx) const
     // uniquely addressable members.
     // Maximum HFA and HVA size is 64 bytes (4 x fp128 or 16bytes vector)
     size_t dsz = jl_datatype_size(dt);
-    if (dsz > 64 || !dt->layout || dt->layout->npointers || dt->layout->flags.haspadding)
+    if (dsz > 64 || !dt->layout || dt->layout->npointers || !dt->layout->flags.isbitsegal || dt->layout->flags.haspadding)
         return NULL;
     nele = 0;
     ElementType eltype;

src/abi_arm.cpp

@@ -82,7 +82,7 @@ size_t isLegalHA(jl_datatype_t *dt, Type *&base, LLVMContext &ctx) const
     if (jl_is_structtype(dt)) {
         // Fast path checks before descending the type hierarchy
         // (4 x 128b vector == 64B max size)
-        if (jl_datatype_size(dt) > 64 || dt->layout->npointers || dt->layout->flags.haspadding)
+        if (jl_datatype_size(dt) > 64 || dt->layout->npointers || !dt->layout->flags.isbitsegal || dt->layout->flags.haspadding)
             return 0;
 
         base = NULL;

src/abi_ppc64le.cpp

@@ -44,7 +44,7 @@ struct ABI_PPC64leLayout : AbiLayout {
 // count the homogeneous floating aggregate size (saturating at max count of 8)
 unsigned isHFA(jl_datatype_t *ty, jl_datatype_t **ty0, bool *hva) const
 {
-    if (jl_datatype_size(ty) > 128 || ty->layout->npointers || ty->layout->flags.haspadding)
+    if (jl_datatype_size(ty) > 128 || ty->layout->npointers || !ty->layout->flags.isbitsegal || ty->layout->flags.haspadding)
         return 9;
 
     size_t i, l = ty->layout->nfields;

src/ccall.cpp

@@ -554,8 +554,8 @@ static Value *julia_to_native(
     // pass the address of an alloca'd thing, not a box
     // since those are immutable.
     Value *slot = emit_static_alloca(ctx, to);
-    unsigned align = julia_alignment(jlto);
-    cast<AllocaInst>(slot)->setAlignment(Align(align));
+    Align align(julia_alignment(jlto));
+    cast<AllocaInst>(slot)->setAlignment(align);
     setName(ctx.emission_context, slot, "native_convert_buffer");
     if (!jvinfo.ispointer()) {
         jl_aliasinfo_t ai = jl_aliasinfo_t::fromTBAA(ctx, jvinfo.tbaa);
@@ -2230,7 +2230,7 @@ jl_cgval_t function_sig_t::emit_a_ccall(
                 Value *strct = emit_allocobj(ctx, (jl_datatype_t*)rt, true);
                 setName(ctx.emission_context, strct, "ccall_ret_box");
                 MDNode *tbaa = jl_is_mutable(rt) ? ctx.tbaa().tbaa_mutab : ctx.tbaa().tbaa_immut;
-                int boxalign = julia_alignment(rt);
+                Align boxalign(julia_alignment(rt));
                 // copy the data from the return value to the new struct
                 const DataLayout &DL = ctx.builder.GetInsertBlock()->getModule()->getDataLayout();
                 auto resultTy = result->getType();
@@ -2240,8 +2240,8 @@ jl_cgval_t function_sig_t::emit_a_ccall(
                     // When this happens, cast through memory.
                     auto slot = emit_static_alloca(ctx, resultTy);
                     setName(ctx.emission_context, slot, "type_pun_slot");
-                    slot->setAlignment(Align(boxalign));
-                    ctx.builder.CreateAlignedStore(result, slot, Align(boxalign));
+                    slot->setAlignment(boxalign);
+                    ctx.builder.CreateAlignedStore(result, slot, boxalign);
                     jl_aliasinfo_t ai = jl_aliasinfo_t::fromTBAA(ctx, tbaa);
                     emit_memcpy(ctx, strct, ai, slot, ai, rtsz, boxalign, boxalign);
                 }