[BOLT] Fix handling of ambiguous jump table entries

bolt/lib/Core/BinaryBasicBlock.cpp

@@ -103,9 +103,18 @@ bool BinaryBasicBlock::validateSuccessorInvariants() {
         Valid &= (Sym == Function->getFunctionEndLabel() ||
                   Sym == Function->getFunctionEndLabel(getFragmentNum()));
         if (!Valid) {
-          BC.errs() << "BOLT-WARNING: Jump table contains illegal entry: "
-                    << Sym->getName() << "\n";
+          const BinaryFunction *TargetBF = BC.getFunctionForSymbol(Sym);
+          if (TargetBF) {
+            // It's possible for another function to be in the jump table entry
+            // as a result of built-in unreachable.
+            Valid = true;
+          } else {
+            BC.errs() << "BOLT-WARNING: Jump table contains illegal entry: "
+                      << Sym->getName() << "\n";
+          }
         }
+        if (!Valid)
+          break;
       }
     }
   } else {

bolt/lib/Core/BinaryFunction.cpp

@@ -1959,7 +1959,9 @@ void BinaryFunction::postProcessJumpTables() {
             return EntryAddress == Parent->getAddress() + Parent->getSize();
           });
       if (IsBuiltinUnreachable) {
-        MCSymbol *Label = getOrCreateLocalLabel(EntryAddress, true);
+        BinaryFunction *TargetBF = BC.getBinaryFunctionAtAddress(EntryAddress);
+        MCSymbol *Label = TargetBF ? TargetBF->getSymbol()
+                                   : getOrCreateLocalLabel(EntryAddress, true);
         JT.Entries.push_back(Label);
         continue;
       }

bolt/lib/Passes/IndirectCallPromotion.cpp

@@ -261,10 +261,7 @@ IndirectCallPromotion::getCallTargets(BinaryBasicBlock &BB,
     for (size_t I = Range.first; I < Range.second; ++I, JI += JIAdj) {
       MCSymbol *Entry = JT->Entries[I];
       const BinaryBasicBlock *ToBB = BF.getBasicBlockForLabel(Entry);
-      assert(ToBB || Entry == BF.getFunctionEndLabel() ||
-             Entry == BF.getFunctionEndLabel(FragmentNum::cold()));
-      if (Entry == BF.getFunctionEndLabel() ||
-          Entry == BF.getFunctionEndLabel(FragmentNum::cold()))
+      if (!ToBB)
         continue;
       const Location To(Entry);
       const BinaryBasicBlock::BinaryBranchInfo &BI = BB.getBranchInfo(*ToBB);

bolt/test/X86/jump-table-ambiguous-unreachable.s

@@ -0,0 +1,87 @@
+## Check that llvm-bolt correctly updates ambiguous jump table entries that
+## can correspond to either builtin_unreachable() or could be a pointer to
+## the next function.
+
+# REQUIRES: system-linux
+
+# RUN: llvm-mc -filetype=obj -triple x86_64-unknown-unknown %s -o %t.o
+# RUN: %clang %cflags %t.o -o %t.exe -no-pie -Wl,-q
+
+# RUN: llvm-bolt %t.exe --print-normalized --print-only=foo -o %t.out \
+# RUN:   2>&1 | FileCheck %s
+
+
+
+  .text
+  .globl _start
+  .type _start, %function
+_start:
+  .cfi_startproc
+  call foo
+  ret
+  .cfi_endproc
+  .size _start, .-_start
+
+  .globl foo
+  .type foo, %function
+foo:
+	.cfi_startproc
+.LBB00:
+          movq	0x8(%rdi), %rdi
+          movzbl	0x1(%rdi), %eax
+.LBB00_br:
+	        jmpq	*"JUMP_TABLE/foo.0"(,%rax,8)
+# CHECK:  jmpq {{.*}} # JUMPTABLE
+# CHECK-NEXT: Successors: {{.*}}, {{.*}}, {{.*}}, {{.*}}, {{.*}}
+
+.Ltmp87085:
+	xorl	%eax, %eax
+	retq
+
+.Ltmp87086:
+	cmpb	$0x0, 0x8(%rdi)
+	setne	%al
+	retq
+
+.Ltmp87088:
+	movb	$0x1, %al
+	retq
+
+.Ltmp87087:
+	movzbl	0x14(%rdi), %eax
+	andb	$0x2, %al
+	shrb	%al
+	retq
+
+	.cfi_endproc
+.size foo, .-foo
+
+  .globl bar
+  .type bar, %function
+bar:
+	.cfi_startproc
+  ret
+	.cfi_endproc
+  .size bar, .-bar
+
+# Jump tables
+.section .rodata
+  .global jump_table
+jump_table:
+"JUMP_TABLE/foo.0":
+  .quad bar
+  .quad	.Ltmp87085
+  .quad bar
+  .quad	.Ltmp87086
+  .quad	.Ltmp87087
+  .quad	.LBB00
+  .quad	.Ltmp87088
+  .quad bar
+  .quad	.LBB00
+
+# CHECK: Jump table {{.*}} for function foo
+# CHECK-NEXT: 0x{{.*}} : bar
+# CHECK-NEXT: 0x{{.*}} :
+# CHECK-NEXT: 0x{{.*}} : bar
+# CHECK-NEXT: 0x{{.*}} :
+# CHECK-NEXT: 0x{{.*}} :