[llvm] [RISCV][MC] Implement evaluateBranch for auipc+jalr pairs (PR #65480)

[Alexander Richardson via llvm-commits]

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@@ -114,10 +114,40 @@ static MCTargetStreamer *createRISCVNullTargetStreamer(MCStreamer &S) {
 namespace {
 
 class RISCVMCInstrAnalysis : public MCInstrAnalysis {
+  std::optional<int64_t> GPRState[31];
+
+  void setGPRState(unsigned Reg, int64_t Value) {
+    assert(Reg >= RISCV::X0 && Reg <= RISCV::X31 && "Invalid GPR reg");
+
+    if (Reg != RISCV::X0)
+      GPRState[Reg - RISCV::X1] = Value;
+  }
+
+  std::optional<int64_t> getGPRState(unsigned Reg) const {
+    assert(Reg >= RISCV::X0 && Reg <= RISCV::X31 && "Invalid GPR reg");
+
+    if (Reg == RISCV::X0)
+      return 0;
+    return GPRState[Reg - RISCV::X1];
+  }
+
 public:
   explicit RISCVMCInstrAnalysis(const MCInstrInfo *Info)
       : MCInstrAnalysis(Info) {}
 
+  void resetState() override {
+    std::fill(std::begin(GPRState), std::end(GPRState), std::nullopt);
+  }
+
+  void updateState(const MCInst &Inst, uint64_t Addr) override {
+    switch (Inst.getOpcode()) {
+    case RISCV::AUIPC:
+      setGPRState(Inst.getOperand(0).getReg(),
+                  Addr + (Inst.getOperand(1).getImm() << 12));
+      break;
+    }
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arichardson wrote:

This does not look safe to me, you will also have to invalidate the state for the destination register(s) for unhandled instructions otherwise you might report a wrong value.

https://github.com/llvm/llvm-project/pull/65480