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Fix GC preserve optimization #24475

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merged 1 commit into from
Nov 6, 2017
Merged

Fix GC preserve optimization #24475

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26 changes: 19 additions & 7 deletions src/llvm-alloc-opt.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -58,6 +58,24 @@ static bool isBundleOperand(CallInst *call, unsigned idx)
#endif
}

static void removeGCPreserve(CallInst *call, Instruction *val)
{
auto replace = ConstantPointerNull::get(cast<PointerType>(val->getType()));
call->replaceUsesOfWith(val, replace);
for (auto &arg: call->arg_operands()) {
if (!isa<Constant>(arg.get())) {
return;
}
}
while (!call->use_empty()) {
auto end = cast<Instruction>(*call->user_begin());
// gc_preserve_end returns void.
assert(end->use_empty());
end->eraseFromParent();
}
call->eraseFromParent();
}

/**
* Promote `julia.gc_alloc_obj` which do not have escaping root to a alloca.
* Uses that are not considered to escape the object (i.e. heap address) includes,
Expand Down Expand Up @@ -608,13 +626,7 @@ void AllocOpt::replaceUsesWith(Instruction *orig_inst, Instruction *new_inst,
}
// Also remove the preserve intrinsics so that it can be better optimized.
if (gc_preserve_begin && gc_preserve_begin == call->getCalledFunction()) {
while (!call->use_empty()) {
auto end = cast<Instruction>(*call->user_begin());
// gc_preserve_end returns void.
assert(end->use_empty());
end->eraseFromParent();
}
call->eraseFromParent();
removeGCPreserve(call, orig_i);
return;
}
if (auto intrinsic = dyn_cast<IntrinsicInst>(call)) {
Expand Down
40 changes: 40 additions & 0 deletions test/llvmpasses/alloc-opt2.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -46,8 +46,48 @@ L3:
""")
# CHECK-LABEL: }

# CHECK-LABEL: @preserve_branches2
# CHECK: alloca i64
# CHECK: call %jl_value_t*** @julia.ptls_states()
# CHECK: L1:
# CHECK-NEXT: call void @llvm.lifetime.start{{.*}}(i64 8,
# CHECK-NEXT: @llvm.julia.gc_preserve_begin{{.*}}%jl_value_t addrspace(10)* %v2
# CHECK-NEXT: @external_function()
# CHECK-NEXT: br i1 %b2, label %L2, label %L3

# CHECK: L2:
# CHECK-NOT: call void @llvm.lifetime.end{{.*}}(i64 8,
# CHECK: @external_function()
# CHECK-NEXT: br label %L3

# CHECK: L3:
# CHECK-NEXT: call void @llvm.lifetime.end{{.*}}(i64 8,
println("""
define void @preserve_branches2(i8* %fptr, i1 %b, i1 %b2) {
%ptls = call %jl_value_t*** @julia.ptls_states()
%ptls_i8 = bitcast %jl_value_t*** %ptls to i8*
%v2 = call %jl_value_t addrspace(10)* @external_function2()
br i1 %b, label %L1, label %L3

L1:
%v = call noalias %jl_value_t addrspace(10)* @julia.gc_alloc_obj(i8* %ptls_i8, $isz 8, %jl_value_t addrspace(10)* @tag)
%tok = call token (...) @llvm.julia.gc_preserve_begin(%jl_value_t addrspace(10)* %v, %jl_value_t addrspace(10)* %v2)
call void @external_function()
br i1 %b2, label %L2, label %L3

L2:
call void @external_function()
br label %L3

L3:
ret void
}
""")
# CHECK-LABEL: }

println("""
declare void @external_function()
declare %jl_value_t addrspace(10)* @external_function2()
declare %jl_value_t*** @julia.ptls_states()
declare noalias %jl_value_t addrspace(10)* @julia.gc_alloc_obj(i8*, $isz, %jl_value_t addrspace(10)*)
declare i64 @julia.pointer_from_objref(%jl_value_t addrspace(11)*)
Expand Down