[BOLT] Tail duplication: disable const/copy propagation by default as a workaround

Summary:
Disable const/copy propagation as a bug workaround.
Also add the debug logging in aggressive duplication.

(cherry picked from FBD32774744)

bolt/lib/Passes/TailDuplication.cpp

@@ -12,6 +12,8 @@
 
 #include <numeric>
 
+#define DEBUG_TYPE "taildup"
+
 using namespace llvm;
 
 namespace opts {
@@ -37,6 +39,11 @@ static cl::opt<unsigned> TailDuplicationMaximumDuplication(
     cl::desc("maximum size of duplicated blocks (in bytes)"), cl::ZeroOrMore,
     cl::ReallyHidden, cl::init(64), cl::cat(BoltOptCategory));
 
+static cl::opt<bool> TailDuplicationConstCopyPropagation(
+    "tail-duplication-const-copy-propagation",
+    cl::desc("enable const and copy propagation after tail duplication"),
+    cl::ReallyHidden, cl::init(false), cl::cat(BoltOptCategory));
+
 } // namespace opts
 
 namespace llvm {
@@ -254,9 +261,14 @@ TailDuplication::aggressiveCodeToDuplicate(BinaryBasicBlock &BB) const {
   std::vector<BinaryBasicBlock *> BlocksToDuplicate;
   BinaryBasicBlock *CurrBB = &BB;
   while (CurrBB) {
+    LLVM_DEBUG(dbgs() << "Aggressive tail duplication: adding "
+                      << CurrBB->getName() << " to duplication list\n";);
     BlocksToDuplicate.push_back(CurrBB);
 
     if (CurrBB->hasJumpTable()) {
+      LLVM_DEBUG(dbgs() << "Aggressive tail duplication: clearing duplication "
+                           "list due to a JT in "
+                        << CurrBB->getName() << '\n';);
       BlocksToDuplicate.clear();
       break;
     }
@@ -273,8 +285,12 @@ TailDuplication::aggressiveCodeToDuplicate(BinaryBasicBlock &BB) const {
       if (CurrBB->getConditionalSuccessor(false)->getLayoutIndex() ==
               CurrBB->getLayoutIndex() + 1 ||
           CurrBB->getConditionalSuccessor(true)->getLayoutIndex() ==
-              CurrBB->getLayoutIndex() + 1)
+              CurrBB->getLayoutIndex() + 1) {
+        LLVM_DEBUG(dbgs() << "Aggressive tail duplication: clearing "
+                             "duplication list, can't find a simple stream at "
+                          << CurrBB->getName() << '\n';);
         BlocksToDuplicate.clear();
+      }
       break;
     }
 
@@ -291,8 +307,14 @@ TailDuplication::aggressiveCodeToDuplicate(BinaryBasicBlock &BB) const {
       [](int value, BinaryBasicBlock *p) {
         return value + p->getOriginalSize();
       });
-  if (DuplicationByteCount > opts::TailDuplicationMaximumDuplication)
+  if (DuplicationByteCount > opts::TailDuplicationMaximumDuplication) {
+    LLVM_DEBUG(dbgs() << "Aggressive tail duplication: duplication byte count ("
+                      << DuplicationByteCount << ") exceeds maximum "
+                      << opts::TailDuplicationMaximumDuplication << '\n';);
     BlocksToDuplicate.clear();
+  }
+  LLVM_DEBUG(dbgs() << "Aggressive tail duplication: found "
+                    << BlocksToDuplicate.size() << " blocks to duplicate\n";);
   return BlocksToDuplicate;
 }
 
@@ -401,18 +423,22 @@ void TailDuplication::runOnFunction(BinaryFunction &Function) {
       BlocksToDuplicate = aggressiveCodeToDuplicate(*Succ);
     else
       BlocksToDuplicate = moderateCodeToDuplicate(*Succ);
-    if (BlocksToDuplicate.size() > 0) {
-      PossibleDuplications++;
-      PossibleDuplicationsDynamicCount += BB->getExecutionCount();
-      std::vector<BinaryBasicBlock *> DuplicatedBlocks =
-          tailDuplicate(*BB, BlocksToDuplicate);
-      constantAndCopyPropagate(*BB, DuplicatedBlocks);
-      BinaryBasicBlock *FirstBB = BlocksToDuplicate[0];
-      if (FirstBB->pred_size() == 1) {
-        BinaryBasicBlock *PredBB = *FirstBB->pred_begin();
-        if (PredBB->succ_size() == 1)
-          constantAndCopyPropagate(*PredBB, BlocksToDuplicate);
-      }
+
+    if (BlocksToDuplicate.size() == 0)
+      continue;
+    PossibleDuplications++;
+    PossibleDuplicationsDynamicCount += BB->getExecutionCount();
+    std::vector<BinaryBasicBlock *> DuplicatedBlocks =
+        tailDuplicate(*BB, BlocksToDuplicate);
+    if (!opts::TailDuplicationConstCopyPropagation)
+      continue;
+
+    constantAndCopyPropagate(*BB, DuplicatedBlocks);
+    BinaryBasicBlock *FirstBB = BlocksToDuplicate[0];
+    if (FirstBB->pred_size() == 1) {
+      BinaryBasicBlock *PredBB = *FirstBB->pred_begin();
+      if (PredBB->succ_size() == 1)
+        constantAndCopyPropagate(*PredBB, BlocksToDuplicate);
     }
   }
 }

bolt/test/X86/tail-duplication-prop-bug.s

@@ -0,0 +1,40 @@
+# This reproduces a bug in aggressive tail duplication/copy propagation.
+# XFAIL: *
+
+# REQUIRES: system-linux
+# RUN: llvm-mc -filetype=obj -triple x86_64-unknown-unknown %s -o %t.o
+# RUN: link_fdata %s %t.o %t.fdata
+# RUN: llvm-strip --strip-unneeded %t.o
+# RUN: %clang %cflags %t.o -o %t.exe -Wl,-q -nostdlib
+# RUN: llvm-bolt %t.exe -o %t.out -data %t.fdata -relocs \
+# RUN:   -tail-duplication=1 -tail-duplication-aggressive=1 \
+# RUN:   -tail-duplication-const-copy-propagation=1
+
+  .globl a
+a:
+	.cfi_startproc
+	jmpq	*JT(,%rcx,8)
+b:
+	jb	d
+# FDATA: 1 a #b# 1 a #d# 6 60
+e:
+	cmpl	%eax, %ebx
+f:
+	jmp	g
+# FDATA: 1 a #f# 1 a #g# 0 8
+d:
+	movl	$0x1, %ebx
+	jmp	e
+	jmp	g
+h:
+	jmp	h
+i:
+	jne	j
+g:
+	jmp	g
+j:
+	.cfi_endproc
+.rodata
+JT:
+	.quad	b
+	.quad	i