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aarch64/llvm: Handle processing of leaf nodes

This commit is contained in:
kd-11 2024-08-12 13:52:26 +03:00 committed by kd-11
parent 6535d461be
commit 0b62385ddb
2 changed files with 188 additions and 12 deletions
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184
rpcs3/Emu/CPU/Backends/AArch64JIT.cpp
View File

@ -47,7 +47,7 @@ namespace aarch64
continue;
}
if (llvm::dyn_cast<llvm::ReturnInst>(&*bit))
if (llvm::isa<llvm::ReturnInst>(&*bit))
{
if (auto ci = llvm::dyn_cast<llvm::CallInst>(&*prev))
{
@ -63,7 +63,7 @@ namespace aarch64
}
}
function_info_t GHC_frame_preservation_pass::preprocess_function(llvm::Function& f)
function_info_t GHC_frame_preservation_pass::preprocess_function(const llvm::Function& f)
{
function_info_t result{};
result.instruction_count = f.getInstructionCount();
@ -100,6 +100,7 @@ namespace aarch64
// This is another thing to be moved to a MachineFunction pass. Ideally we should check the instruction stream for writes to LR and reload it on exit.
// For now, assume it is dirtied if the function is of any reasonable length.
result.clobbers_x30 = result.instruction_count > 32;
result.is_leaf = true;
for (auto& bb : f)
{
@ -107,8 +108,23 @@ namespace aarch64
{
if (auto ci = llvm::dyn_cast<llvm::CallInst>(&inst))
{
if (llvm::isa<llvm::InlineAsm>(ci->getCalledOperand()))
{
// Inline ASM blocks are ignored
continue;
}
result.num_external_calls++;
result.clobbers_x30 |= (!ci->isTailCall());
if (ci->isTailCall())
{
// This is not a leaf if it has at least one exit point / terminator that is not a return instruction.
result.is_leaf = false;
}
else
{
// Returning calls always clobber x30
result.clobbers_x30 = true;
}
}
}
}
@ -116,7 +132,7 @@ namespace aarch64
return result;
}
instruction_info_t GHC_frame_preservation_pass::decode_instruction(llvm::Function& f, llvm::Instruction* i)
instruction_info_t GHC_frame_preservation_pass::decode_instruction(const llvm::Function& f, const llvm::Instruction* i)
{
instruction_info_t result{};
if (auto ci = llvm::dyn_cast<llvm::CallInst>(i))
@ -202,7 +218,7 @@ namespace aarch64
return result;
}
gpr GHC_frame_preservation_pass::get_base_register_for_call(const std::string& callee_name)
gpr GHC_frame_preservation_pass::get_base_register_for_call(const std::string& callee_name, gpr default_reg)
{
// We go over the base_register_lookup table and find the first matching pattern
for (const auto& pattern : m_config.base_register_lookup)
@ -213,8 +229,7 @@ namespace aarch64
}
}
// Default is x19
return aarch64::x19;
return default_reg;
}
void GHC_frame_preservation_pass::run(llvm::IRBuilder<>* irb, llvm::Function& f)
@ -262,6 +277,16 @@ namespace aarch64
// Force tail calls on all terminators
force_tail_call_terminators(f);
// Check for leaves
if (function_info.is_leaf && !m_config.use_stack_frames)
{
// Sanity check. If this function had no returning calls, it should have been omitted from processing.
ensure(function_info.clobbers_x30, "Function has no terminator and no non-tail calls but was allowed for frame processing!");
DPRINT("Function %s is a leaf.", this_name.c_str());
process_leaf_function(irb, f);
return;
}
// Asm snippets for patching stack frame
std::string frame_prologue, frame_epilogue;
@ -413,6 +438,149 @@ namespace aarch64
}
}
ensure(terminator_found, "Could not find terminator for function!");
if (!terminator_found)
{
// If we got here, we must be using stack frames.
ensure(function_info.is_leaf && function_info.stack_frame_size > 0, "Leaf function was processed without using stack frames!");
// We want to insert a frame cleanup at the tail at every return instruction we find.
for (auto& bb : f)
{
for (auto& i : bb)
{
if (is_ret_instruction(&i))
{
irb->SetInsertPoint(&i);
LLVM_ASM_VOID(frame_epilogue, irb, f.getContext());
}
}
}
}
}
bool GHC_frame_preservation_pass::is_ret_instruction(const llvm::Instruction* i)
{
if (llvm::isa<llvm::ReturnInst>(i))
{
return true;
}
// Check for inline asm invoking "ret". This really shouldn't be a thing, but it is present in SPULLVMRecompiler for some reason.
if (auto ci = llvm::dyn_cast<llvm::CallInst>(i))
{
if (auto asm_ = llvm::dyn_cast<llvm::InlineAsm>(ci->getCalledOperand()))
{
if (asm_->getAsmString() == "ret")
{
return true;
}
}
}
return false;
}
bool GHC_frame_preservation_pass::is_inlined_call(const llvm::CallInst* ci)
{
const auto callee = ci->getCalledFunction();
if (!callee)
{
// Indirect BLR
return false;
}
const std::string callee_name = callee->getName().str();
if (callee_name.starts_with("llvm."))
{
// Intrinsic
return true;
}
if (callee->hasFnAttribute(llvm::Attribute::AlwaysInline))
{
// Assume LLVM always obeys this
return true;
}
return false;
}
void GHC_frame_preservation_pass::process_leaf_function(llvm::IRBuilder<>* irb, llvm::Function& f)
{
// Leaf functions have no true external calls.
// After every external call, restore LR from the thread context register.
bool restore_LR = false;
gpr thread_context_reg = aarch64::x19;
const auto restore_x30 = [&](llvm::Instruction* where)
{
const auto x30_tail_restore = fmt::format(
"ldr x30, [x%u, #%u];\n", // Load x30 from thread context
static_cast<u32>(thread_context_reg),
m_config.hypervisor_context_offset);
ensure(where);
irb->SetInsertPoint(where);
LLVM_ASM_VOID(x30_tail_restore, irb, f.getContext());
};
for (auto &bb : f)
{
for (auto bit = bb.begin(); bit != bb.end();)
{
if (restore_LR)
{
restore_x30(llvm::dyn_cast<llvm::Instruction>(bit));
restore_LR = false;
}
if (auto ci = llvm::dyn_cast<llvm::CallInst>(bit))
{
// Returning call?
if (is_inlined_call(ci))
{
++bit;
continue;
}
const auto callee = ci->getCalledFunction();
const std::string callee_name = callee ? callee->getName().str() : "__indirect";
auto base_reg = get_base_register_for_call(callee_name, m_config.base_register_lookup.empty() ? gpr::x19 : gpr::xzr);
// Check if the call is unexpected. We cannot guarantee that the reload is well-formed in such scenarios
if (base_reg == gpr::xzr)
{
if (callee)
{
// We don't know what we're dealing with here
DPRINT("Unexpected call to %s. We cannot guarantee sane codegen!", callee_name.c_str());
}
// Assume x19
base_reg = gpr::x19;
}
restore_LR = true;
thread_context_reg = base_reg;
}
if (m_config.debug_info && is_ret_instruction(llvm::dyn_cast<llvm::Instruction>(bit)))
{
// We need to save the chain return point.
LLVM_ASM_VOID(
"mov x29, x28;\n"
"mov x28, x27;\n"
"adr x27, .;\n",
irb, f.getContext());
}
if (bit != bb.end())
{
++bit;
}
}
}
ensure(!restore_LR, "Dangling function call found");
}
}

16
rpcs3/Emu/CPU/Backends/AArch64JIT.h
View File

@ -16,7 +16,8 @@ namespace aarch64
x0 = 0,
x1, x2, x3, x4, x5, x6, x7, x8, x9,
x10, x11, x12, x13, x14, x15, x16, x17, x18, x19,
x20, x21, x22, x23, x24, x25, x26, x27, x28, x29, x30
x20, x21, x22, x23, x24, x25, x26, x27, x28, x29, x30,
xzr, pc, sp
};
// On non-x86 architectures GHC runs stackless. SP is treated as a pointer to scratchpad memory.
@ -30,6 +31,7 @@ namespace aarch64
u32 num_external_calls;
u32 stack_frame_size; // Guessing this properly is critical for vector-heavy functions where spilling is a lot more common
bool clobbers_x30;
bool is_leaf;
};
struct instruction_info_t
@ -60,11 +62,17 @@ namespace aarch64
void force_tail_call_terminators(llvm::Function& f);
function_info_t preprocess_function(llvm::Function& f);
function_info_t preprocess_function(const llvm::Function& f);
instruction_info_t decode_instruction(llvm::Function& f, llvm::Instruction* i);
instruction_info_t decode_instruction(const llvm::Function& f, const llvm::Instruction* i);
gpr get_base_register_for_call(const std::string& callee_name);
bool is_ret_instruction(const llvm::Instruction* i);
bool is_inlined_call(const llvm::CallInst* ci);
gpr get_base_register_for_call(const std::string& callee_name, gpr default_reg = gpr::x19);
void process_leaf_function(llvm::IRBuilder<>* irb, llvm::Function& f);
public:
GHC_frame_preservation_pass(const config_t& configuration);