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AllocOpt: Fix stack lowering where alloca contains boxed and unboxed data (#55306) #55397

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Aug 7, 2024
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AllocOpt: Fix stack lowering where alloca contains boxed and unboxed data (#55306) #55397

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10 changes: 9 additions & 1 deletion src/llvm-alloc-helpers.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -88,6 +88,8 @@ bool AllocUseInfo::addMemOp(Instruction *inst, unsigned opno, uint32_t offset,
memop.isaggr = isa<StructType>(elty) || isa<ArrayType>(elty) || isa<VectorType>(elty);
memop.isobjref = hasObjref(elty);
auto &field = getField(offset, size, elty);
field.second.hasunboxed |= !hasObjref(elty) || (hasObjref(elty) && !isa<PointerType>(elty));

if (field.second.hasobjref != memop.isobjref)
field.second.multiloc = true; // can't split this field, since it contains a mix of references and bits
if (!isstore)
Expand Down Expand Up @@ -189,6 +191,7 @@ void jl_alloc::runEscapeAnalysis(llvm::Instruction *I, EscapeAnalysisRequiredArg
auto elty = inst->getType();
required.use_info.has_unknown_objref |= hasObjref(elty);
required.use_info.has_unknown_objrefaggr |= hasObjref(elty) && !isa<PointerType>(elty);
required.use_info.has_unknown_unboxed |= !hasObjref(elty) || (hasObjref(elty) && !isa<PointerType>(elty));
required.use_info.hasunknownmem = true;
} else if (!required.use_info.addMemOp(inst, 0, cur.offset,
inst->getType(),
Expand Down Expand Up @@ -280,6 +283,7 @@ void jl_alloc::runEscapeAnalysis(llvm::Instruction *I, EscapeAnalysisRequiredArg
auto elty = storev->getType();
required.use_info.has_unknown_objref |= hasObjref(elty);
required.use_info.has_unknown_objrefaggr |= hasObjref(elty) && !isa<PointerType>(elty);
required.use_info.has_unknown_unboxed |= !hasObjref(elty) || (hasObjref(elty) && !isa<PointerType>(elty));
required.use_info.hasunknownmem = true;
} else if (!required.use_info.addMemOp(inst, use->getOperandNo(),
cur.offset, storev->getType(),
Expand All @@ -301,10 +305,14 @@ void jl_alloc::runEscapeAnalysis(llvm::Instruction *I, EscapeAnalysisRequiredArg
}
required.use_info.hasload = true;
auto storev = isa<AtomicCmpXchgInst>(inst) ? cast<AtomicCmpXchgInst>(inst)->getNewValOperand() : cast<AtomicRMWInst>(inst)->getValOperand();
Type *elty = storev->getType();
if (cur.offset == UINT32_MAX || !required.use_info.addMemOp(inst, use->getOperandNo(),
cur.offset, storev->getType(),
cur.offset, elty,
true, required.DL)) {
LLVM_DEBUG(dbgs() << "Atomic inst has unknown offset\n");
required.use_info.has_unknown_objref |= hasObjref(elty);
required.use_info.has_unknown_objrefaggr |= hasObjref(elty) && !isa<PointerType>(elty);
required.use_info.has_unknown_unboxed |= !hasObjref(elty) || (hasObjref(elty) && !isa<PointerType>(elty));
required.use_info.hasunknownmem = true;
}
required.use_info.refload = true;
Expand Down
7 changes: 7 additions & 0 deletions src/llvm-alloc-helpers.h
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Expand Up @@ -46,6 +46,8 @@ namespace jl_alloc {
bool hasaggr:1;
bool multiloc:1;
bool hasload:1;
// The alloc has a unboxed object at this offset.
bool hasunboxed:1;
llvm::Type *elty;
llvm::SmallVector<MemOp,4> accesses;
Field(uint32_t size, llvm::Type *elty)
Expand All @@ -54,6 +56,7 @@ namespace jl_alloc {
hasaggr(false),
multiloc(false),
hasload(false),
hasunboxed(false),
elty(elty)
{
}
Expand Down Expand Up @@ -93,6 +96,9 @@ namespace jl_alloc {
// The alloc has an aggregate Julia object reference not in an explicit field.
bool has_unknown_objrefaggr:1;

// The alloc has an unboxed object at an unknown offset.
bool has_unknown_unboxed:1;

void reset()
{
escaped = false;
Expand All @@ -107,6 +113,7 @@ namespace jl_alloc {
haserror = false;
has_unknown_objref = false;
has_unknown_objrefaggr = false;
has_unknown_unboxed = false;
uses.clear();
preserves.clear();
memops.clear();
Expand Down
15 changes: 15 additions & 0 deletions src/llvm-alloc-opt.cpp
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Expand Up @@ -252,10 +252,12 @@ void Optimizer::optimizeAll()
removeAlloc(orig);
continue;
}
bool has_unboxed = use_info.has_unknown_unboxed;
bool has_ref = use_info.has_unknown_objref;
bool has_refaggr = use_info.has_unknown_objrefaggr;
for (auto memop: use_info.memops) {
auto &field = memop.second;
has_unboxed |= field.hasunboxed;
if (field.hasobjref) {
has_ref = true;
// This can be relaxed a little based on hasload
Expand Down Expand Up @@ -284,6 +286,19 @@ void Optimizer::optimizeAll()
splitOnStack(orig);
continue;
}
// The move to stack code below, if has_ref is set, changes the allocation to an array of jlvalue_t's. This is fine
// if all objects are jlvalue_t's. However, if part of the allocation is an unboxed value (e.g. it is a { float, jlvaluet }),
// then moveToStack will create a [2 x jlvaluet] bitcast to { float, jlvaluet }.
// This later causes the GC rooting pass, to miss-characterize the float as a pointer to a GC value
if (has_unboxed && has_ref) {
REMARK([&]() {
return OptimizationRemarkMissed(DEBUG_TYPE, "Escaped", orig)
<< "GC allocation could not be split since it contains both boxed and unboxed values, unable to move to stack " << ore::NV("GC Allocation", orig);
});
if (use_info.hastypeof)
optimizeTag(orig);
continue;
}
REMARK([&](){
return OptimizationRemark(DEBUG_TYPE, "Stack Move Allocation", orig)
<< "GC allocation moved to stack " << ore::NV("GC Allocation", orig);
Expand Down
41 changes: 41 additions & 0 deletions test/llvmpasses/alloc-opt-bits.ll
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@@ -0,0 +1,41 @@
; This file is a part of Julia. License is MIT: https://julialang.org/license


; RUN: opt -enable-new-pm=0 --opaque-pointers=0 -load libjulia-codegen%shlibext -AllocOpt -S %s | FileCheck %s --check-prefixes=CHECK,TYPED
; RUN: opt -enable-new-pm=1 --opaque-pointers=0 --load-pass-plugin=libjulia-codegen%shlibext -passes='function(AllocOpt)' -S %s | FileCheck %s --check-prefixes=CHECK,TYPED

; RUN: opt -enable-new-pm=0 --opaque-pointers=1 -load libjulia-codegen%shlibext -AllocOpt -S %s | FileCheck %s --check-prefixes=CHECK,OPAQUE
; RUN: opt -enable-new-pm=1 --opaque-pointers=1 --load-pass-plugin=libjulia-codegen%shlibext -passes='function(AllocOpt)' -S %s | FileCheck %s --check-prefixes=CHECK,OPAQUE


@tag = external addrspace(10) global {}

@glob = external addrspace(10) global {}

; Test that the gc_preserve intrinsics are deleted directly.

; CHECK-LABEL: @ptr_and_bits
; CHECK-NOT: alloca
; OPAQUE: call noalias ptr addrspace(10) @julia.gc_alloc_obj
; TYPED: call noalias {} addrspace(10)* @julia.gc_alloc_obj

define void @ptr_and_bits(i8* %fptr, i1 %b, i1 %b2, i32 %idx) {
%pgcstack = call {}*** @julia.get_pgcstack()
%gcstack = bitcast {}*** %pgcstack to {}**
%current_task = getelementptr inbounds {}*, {}** %gcstack, i64 -12
%v = call noalias {} addrspace(10)* @julia.gc_alloc_obj({}** %current_task, i64 16, {} addrspace(10)* @tag)
%v2 = bitcast {} addrspace(10)* %v to { i64, {} addrspace(10)* } addrspace(10)*
%g0 = getelementptr { i64, {} addrspace(10)* }, { i64, {} addrspace(10)* } addrspace(10)* %v2, i32 %idx, i32 1
store {} addrspace(10)* @glob, {} addrspace(10)* addrspace(10)* %g0

%g1 = getelementptr { i64, {} addrspace(10)* }, { i64, {} addrspace(10)* } addrspace(10)* %v2, i32 %idx, i32 0
store i64 7, i64 addrspace(10)* %g1

%res = load {} addrspace(10)*, {} addrspace(10)* addrspace(10)* %g0
%res2 = load i64, i64 addrspace(10)* %g1
ret void
}

declare noalias {} addrspace(10)* @julia.gc_alloc_obj({}**, i64, {} addrspace(10)*)

declare {}*** @julia.get_pgcstack()