Revert "Encode address offsets of basic blocks relative to the end of the previous basic blocks."

[rahmanl]

Summary

This reverts commit 029283c1c0d8d06fbf000f5682c56b8595a1101f.
The code in ELFFile::decodeBBAddrMap was not changed in the submitted patch.

llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp

void AsmPrinter::emitBBAddrMapSection(const MachineFunction &MF) {
 
   const MCSymbol *FunctionSymbol = getFunctionBegin();
 
   OutStreamer->PushSection();
   OutStreamer->SwitchSection(BBAddrMapSection);
   OutStreamer->emitSymbolValue(FunctionSymbol, getPointerSize());
   // Emit the total number of basic blocks in this function.
   OutStreamer->emitULEB128IntValue(MF.size());
-  const MCSymbol *PrevMBBEndSymbol = FunctionSymbol;
   // Emit BB Information for each basic block in the funciton.
   for (const MachineBasicBlock &MBB : MF) {
     const MCSymbol *MBBSymbol =
         MBB.isEntryBlock() ? FunctionSymbol : MBB.getSymbol();
-    // Emit the basic block offset relative to the end of the previous block.
-    // This is zero unless the block is padded due to alignment.
-    emitLabelDifferenceAsULEB128(MBBSymbol, PrevMBBEndSymbol);
+    // Emit the basic block offset.
+    emitLabelDifferenceAsULEB128(MBBSymbol, FunctionSymbol);
     // Emit the basic block size. When BBs have alignments, their size cannot
     // always be computed from their offsets.
     emitLabelDifferenceAsULEB128(MBB.getEndSymbol(), MBBSymbol);
     OutStreamer->emitULEB128IntValue(getBBAddrMapMetadata(MBB));
-    PrevMBBEndSymbol = MBB.getEndSymbol();
   }
   OutStreamer->PopSection();
 }
 
 void AsmPrinter::emitPseudoProbe(const MachineInstr &MI) {
   auto GUID = MI.getOperand(0).getImm();
   auto Index = MI.getOperand(1).getImm();
   auto Type = MI.getOperand(2).getImm();

llvm/lib/CodeGen/BasicBlockSections.cpp

 //    needs special handling with basic block sections. DebugInfo needs to be
 //    emitted with more relocations as basic block sections can break a
 //    function into potentially several disjoint pieces, and CFI needs to be
 //    emitted per cluster. This also bloats the object file and binary sizes.
 //
 // Basic Block Labels
 // ==================
 //
-// With -fbasic-block-sections=labels, we encode the offsets of BB addresses of
+// With -fbasic-block-sections=labels, we emit the offsets of BB addresses of
 // every function into the .llvm_bb_addr_map section. Along with the function
 // symbols, this allows for mapping of virtual addresses in PMU profiles back to
 // the corresponding basic blocks. This logic is implemented in AsmPrinter. This
 // pass only assigns the BBSectionType of every function to ``labels``.
 //
 //===----------------------------------------------------------------------===//
 
 #include "llvm/ADT/Optional.h"

llvm/test/CodeGen/X86/basic-block-sections-labels.ll

 ; UNIQ:     .section  .llvm_bb_addr_map,"o",@llvm_bb_addr_map,.text._Z3bazb{{$}}
 ;; Verify that with -unique-section-names=false, the unique id of the text section gets assigned to the llvm_bb_addr_map section.
 ; NOUNIQ:   .section  .llvm_bb_addr_map,"o",@llvm_bb_addr_map,.text,unique,1
 ; CHECK-NEXT: .quad .Lfunc_begin0
 ; CHECK-NEXT: .byte 4
 ; CHECK-NEXT: .uleb128 .Lfunc_begin0-.Lfunc_begin0
 ; CHECK-NEXT: .uleb128 .LBB_END0_0-.Lfunc_begin0
 ; CHECK-NEXT: .byte 8
-; CHECK-NEXT: .uleb128 .LBB0_1-.LBB_END0_0
+; CHECK-NEXT: .uleb128 .LBB0_1-.Lfunc_begin0
 ; CHECK-NEXT: .uleb128 .LBB_END0_1-.LBB0_1
 ; CHECK-NEXT: .byte 8
-; CHECK-NEXT: .uleb128 .LBB0_2-.LBB_END0_1
+; CHECK-NEXT: .uleb128 .LBB0_2-.Lfunc_begin0
 ; CHECK-NEXT: .uleb128 .LBB_END0_2-.LBB0_2
 ; CHECK-NEXT: .byte 1
-; CHECK-NEXT: .uleb128 .LBB0_3-.LBB_END0_2
+; CHECK-NEXT: .uleb128 .LBB0_3-.Lfunc_begin0
 ; CHECK-NEXT: .uleb128 .LBB_END0_3-.LBB0_3
 ; CHECK-NEXT: .byte 5

llvm/test/tools/llvm-readobj/ELF/bb-addr-map.test

 # LLVM-NEXT:         Offset: 0x0
 # LLVM-NEXT:         Size: 0x1
 # LLVM-NEXT:         HasReturn: No
 # LLVM-NEXT:         HasTailCall: Yes
 # LLVM-NEXT:         IsEHPad: No
 # LLVM-NEXT:         CanFallThrough: No
 # LLVM-NEXT:       }
 # LLVM-NEXT:       {
-# LLVM-NEXT:         Offset: 0x4
+# LLVM-NEXT:         Offset: 0x3
 # LLVM-NEXT:         Size: 0x4
 # LLVM-NEXT:         HasReturn: Yes
 # LLVM-NEXT:         HasTailCall: No
 # LLVM-NEXT:         IsEHPad: Yes
 # LLVM-NEXT:         CanFallThrough: No
 # LLVM-NEXT:       }
 # LLVM-NEXT:     ]
 # LLVM-NEXT:   }

llvm/tools/llvm-readobj/ELFDumper.cpp

for (const BBAddrMap &AM : *BBAddrMapOrErr) {
         this->reportUniqueWarning(
             "could not identify function symbol for address (0x" +
             Twine::utohexstr(AM.Addr) + ") in " + this->describe(Sec));
       else
         FuncName = this->getStaticSymbolName(FuncSymIndex.front());
       W.printString("Name", FuncName);
 
       ListScope L(W, "BB entries");
-      uint32_t FunctionRelativeAddress = 0;
       for (const BBAddrMap::BBEntry &BBE : AM.BBEntries) {
         DictScope L(W);
-        FunctionRelativeAddress += BBE.Offset;
-        W.printHex("Offset", FunctionRelativeAddress);
+        W.printHex("Offset", BBE.Offset);
         W.printHex("Size", BBE.Size);
-        FunctionRelativeAddress += BBE.Size;
         W.printBoolean("HasReturn", BBE.HasReturn);
         W.printBoolean("HasTailCall", BBE.HasTailCall);
         W.printBoolean("IsEHPad", BBE.IsEHPad);
         W.printBoolean("CanFallThrough", BBE.CanFallThrough);
       }
     }
   }
 }