[BOLT] Fix deadloop bug in taildup

The intent is clearly to push the tail rather than current BB.

Reviewed By: maksfb

Differential Revision: https://reviews.llvm.org/D159289

Author: MANGOPIE3

bolt/lib/Passes/TailDuplication.cpp

@@ -303,7 +303,7 @@ TailDuplication::aggressiveDuplicate(BinaryBasicBlock &BB,
   if (isInCacheLine(BB, Tail))
     return BlocksToDuplicate;
 
-  BinaryBasicBlock *CurrBB = &BB;
+  BinaryBasicBlock *CurrBB = &Tail;
   while (CurrBB) {
     LLVM_DEBUG(dbgs() << "Aggressive tail duplication: adding "
                       << CurrBB->getName() << " to duplication list\n";);

bolt/test/X86/tail-duplication-pass.s

@@ -7,12 +7,21 @@
 # RUN: llvm-bolt %t.exe --data %t.fdata --reorder-blocks=ext-tsp \
 # RUN:    --print-finalized --tail-duplication=moderate \
 # RUN:    --tail-duplication-minimum-offset=1 -o %t.out | FileCheck %s
+# RUN: llvm-bolt %t.exe --data %t.fdata --print-finalized \
+# RUN:    --tail-duplication=aggressive --tail-duplication-minimum-offset=1 \
+# RUN:    -o %t.out | FileCheck %s --check-prefix CHECK-NOLOOP
 
 # FDATA: 1 main 2 1 main #.BB2# 0 10
 # FDATA: 1 main 4 1 main #.BB2# 0 20
 # CHECK: BOLT-INFO: tail duplication modified 1 ({{.*}}%) functions; duplicated 1 blocks (1 bytes) responsible for {{.*}} dynamic executions ({{.*}}% of all block executions)
 # CHECK: BB Layout   : .LBB00, .Ltail-dup0, .Ltmp0, .Ltmp1
 
+# Check that the successor of Ltail-dup0 is .LBB00, not itself.
+# CHECK-NOLOOP: .Ltail-dup0 (1 instructions, align : 1)
+# CHECK-NOLOOP: Predecessors: .LBB00
+# CHECK-NOLOOP: retq
+# CHECK-NOLOOP: .Ltmp0 (1 instructions, align : 1)
+
     .text
     .globl main
     .type main, %function