7fa33773e3
Long tail calls use the following instruction sequence on RISC-V: ``` 1: auipc xi, %pcrel_hi(sym) jalr zero, %pcrel_lo(1b)(xi) ``` Since the second instruction in isolation looks like an indirect branch, this confused BOLT and most functions containing a long tail call got marked with "unknown control flow" and didn't get optimized as a consequence. This patch fixes this by detecting long tail call sequence in `analyzeIndirectBranch`. `FixRISCVCallsPass` also had to be updated to expand long tail calls to `PseudoTAIL` instead of `PseudoCALL`. Besides this, this patch also fixes a minor issue with compressed tail calls (`c.jr`) not being detected. Note that I had to change `BinaryFunction::postProcessIndirectBranches` slightly: the documentation of `MCPlusBuilder::analyzeIndirectBranch` mentions that the [`Begin`, `End`) range contains the instructions immediately preceding `Instruction`. However, in `postProcessIndirectBranches`, *all* the instructions in the BB where passed in the range. This made it difficult to find the preceding instruction so I made sure *only* the preceding instructions are passed.
86 lines
2.2 KiB
C++
86 lines
2.2 KiB
C++
#include "bolt/Passes/FixRISCVCallsPass.h"
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#include "bolt/Core/ParallelUtilities.h"
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#include <iterator>
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using namespace llvm;
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namespace llvm {
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namespace bolt {
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void FixRISCVCallsPass::runOnFunction(BinaryFunction &BF) {
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auto &BC = BF.getBinaryContext();
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auto &MIB = BC.MIB;
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auto *Ctx = BC.Ctx.get();
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for (auto &BB : BF) {
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for (auto II = BB.begin(); II != BB.end();) {
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if (MIB->isCall(*II) && !MIB->isIndirectCall(*II)) {
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auto *Target = MIB->getTargetSymbol(*II);
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assert(Target && "Cannot find call target");
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MCInst OldCall = *II;
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auto L = BC.scopeLock();
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if (MIB->isTailCall(*II))
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MIB->createTailCall(*II, Target, Ctx);
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else
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MIB->createCall(*II, Target, Ctx);
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MIB->moveAnnotations(std::move(OldCall), *II);
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++II;
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continue;
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}
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auto NextII = std::next(II);
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if (NextII == BB.end())
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break;
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if (MIB->isRISCVCall(*II, *NextII)) {
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auto *Target = MIB->getTargetSymbol(*II);
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assert(Target && "Cannot find call target");
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MCInst OldCall = *NextII;
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auto L = BC.scopeLock();
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if (MIB->isTailCall(*NextII))
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MIB->createTailCall(*II, Target, Ctx);
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else
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MIB->createCall(*II, Target, Ctx);
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MIB->moveAnnotations(std::move(OldCall), *II);
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// The original offset was set on the jalr of the auipc+jalr pair. Since
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// the whole pair is replaced by a call, adjust the offset by -4 (the
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// size of a auipc).
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if (std::optional<uint32_t> Offset = MIB->getOffset(*II)) {
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assert(*Offset >= 4 && "Illegal jalr offset");
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MIB->setOffset(*II, *Offset - 4);
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}
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II = BB.eraseInstruction(NextII);
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continue;
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}
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++II;
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}
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}
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}
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void FixRISCVCallsPass::runOnFunctions(BinaryContext &BC) {
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if (!BC.isRISCV() || !BC.HasRelocations)
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return;
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ParallelUtilities::WorkFuncTy WorkFun = [&](BinaryFunction &BF) {
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runOnFunction(BF);
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};
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ParallelUtilities::runOnEachFunction(
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BC, ParallelUtilities::SchedulingPolicy::SP_INST_LINEAR, WorkFun, nullptr,
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"FixRISCVCalls");
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}
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} // namespace bolt
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} // namespace llvm
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