[BOLT] Implement '--assume-abi' option for AArch64

[Kepontry]

Summary

[BOLT] Implement '--assume-abi' option for AArch64

This patch implements the getCalleeSavedRegs function for AArch64,
addressing the issue where the "not implemented" error occurs when
both the --assume-abi option and options related to the
RegAnalysis Pass (e.g., --indirect-call-promotion=all) are enabled.

The beConservative function is utilized to determine the set of
used registers in cases where we have no prior information about
the function. When the --assume-abi option is enabled,
callee-saved registers should not be included in this set.

[yota9]

Hello! Please provide the test for this change.

[Kepontry]

Add a simple testcase.

[yota9]

bolt/lib/Target/AArch64/AArch64MCPlusBuilder.cpp

447

I believe we must add X18 register also, since the ARM ABI says it might be platform-specific, so BOLT must preserve it's value

[Kepontry]

Manually relate the commit https://reviews.llvm.org/rG2d902d0f880498145f70e41a265c1adecb05d089

bolt/lib/Target/AArch64/AArch64MCPlusBuilder.cpp

public:
   }
 
   bool replaceMemOperandDisp(MCInst &Inst, MCOperand Operand) const override {
     MCInst::iterator OI = getMemOperandDisp(Inst);
     *OI = Operand;
     return true;
   }
 
+  void getCalleeSavedRegs(BitVector &Regs) const override {
+    Regs |= getAliases(AArch64::X19);
+    Regs |= getAliases(AArch64::X20);
+    Regs |= getAliases(AArch64::X21);
+    Regs |= getAliases(AArch64::X22);
+    Regs |= getAliases(AArch64::X23);
+    Regs |= getAliases(AArch64::X24);
+    Regs |= getAliases(AArch64::X25);
+    Regs |= getAliases(AArch64::X26);
+    Regs |= getAliases(AArch64::X27);
+    Regs |= getAliases(AArch64::X28);
+    Regs |= getAliases(AArch64::LR);
+    Regs |= getAliases(AArch64::FP);
+  }
+
   const MCExpr *getTargetExprFor(MCInst &Inst, const MCExpr *Expr,
                                  MCContext &Ctx,
                                  uint64_t RelType) const override {
 
     if (isADR(Inst) || RelType == ELF::R_AARCH64_ADR_PREL_LO21 ||
         RelType == ELF::R_AARCH64_TLSDESC_ADR_PREL21) {
       return AArch64MCExpr::create(Expr, AArch64MCExpr::VK_ABS, Ctx);
     } else if (isADRP(Inst) || RelType == ELF::R_AARCH64_ADR_PREL_PG_HI21 ||

bolt/test/assume-abi.test

+# Validate the usage of the `--assume-abi` option in conjunction with
+# CFG-related options.
+
+REQUIRES: system-linux
+
+RUN: %clang %cflags %p/Inputs/hello.c -o %t -Wl,-q
+RUN: llvm-bolt %t -o %t.bolt --assume-abi --indirect-call-promotion=all