[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.

Author: Kepontry

bolt/lib/Target/AArch64/AArch64MCPlusBuilder.cpp

@@ -471,6 +471,22 @@ class AArch64MCPlusBuilder : public MCPlusBuilder {
     return true;
   }
 
+  void getCalleeSavedRegs(BitVector &Regs) const override {
+    Regs |= getAliases(AArch64::X18);
+    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 {

bolt/test/assume-abi.test

@@ -0,0 +1,7 @@
+# Validate the usage of the `--assume-abi` option in conjunction with
+# options related to the RegAnalysis Pass.
+
+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