[BOLT] Support map other function entry address (llvm#101466)

Allow BOLT to map the old address to a new binary address if the old
address is the entry of the function.

bolt/lib/Rewrite/RewriteInstance.cpp

@@ -5509,6 +5509,14 @@ uint64_t RewriteInstance::getNewFunctionOrDataAddress(uint64_t OldAddress) {
   if (const BinaryFunction *BF =
           BC->getBinaryFunctionContainingAddress(OldAddress)) {
     if (BF->isEmitted()) {
+      // If OldAddress is the another entry point of
+      // the function, then BOLT could get the new address.
+      if (BF->isMultiEntry()) {
+        for (const BinaryBasicBlock &BB : *BF)
+          if (BB.isEntryPoint() &&
+              (BF->getAddress() + BB.getOffset()) == OldAddress)
+            return BF->getOutputAddress() + BB.getOffset();
+      }
       BC->errs() << "BOLT-ERROR: unable to get new address corresponding to "
                     "input address 0x"
                  << Twine::utohexstr(OldAddress) << " in function " << *BF

bolt/test/X86/dynamic-relocs-on-entry.s

@@ -0,0 +1,32 @@
+// This test examines whether BOLT can correctly process when
+// dynamic relocation points to other entry points of the
+// function.
+
+# RUN: %clang %cflags -fPIC -pie %s -o %t.exe -nostdlib -Wl,-q
+# RUN: llvm-bolt %t.exe -o %t.bolt > %t.out.txt
+# RUN: readelf -r %t.bolt >> %t.out.txt
+# RUN: llvm-objdump --disassemble-symbols=chain %t.bolt >> %t.out.txt
+# RUN: FileCheck %s --input-file=%t.out.txt
+
+## Check if the new address in `chain` is correctly updated by BOLT
+# CHECK: Relocation section '.rela.dyn' at offset 0x{{.*}} contains 1 entry:
+# CHECK: {{.*}} R_X86_64_RELATIVE [[#%x,ADDR:]]
+# CHECK: [[#ADDR]]: c3 retq
+	.text
+	.type   chain, @function
+chain:
+	movq    $1, %rax
+Label:
+	ret
+	.size   chain, .-chain
+
+	.type   _start, @function
+	.global _start
+_start:
+	jmpq    *.Lfoo(%rip)
+	ret
+	.size   _start, .-_start
+
+	.data
+.Lfoo:
+	.quad Label