[BOLT] Support map other function entry address

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

Author: linsinan1995

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 (auto &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 +1,25 @@
+// This test examines whether BOLT can correctly update 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 | FileCheck %s
+
+    .text
+    .type   chain, @function
+chain:
+    movq    $1, %rax
+Lable:
+    ret
+    .size   chain, .-chain
+    .type   _start, @function
+    .global _start
+_start:
+    jmpq    *.Lfoo(%rip)
+    ret
+    .size   _start, .-_start
+  .data
+.Lfoo:
+  .quad Lable
+
+# CHECK-NOT: BOLT-ERROR