[LLVMbugs] [Bug 2200] New: Wrong generation of multi-stage Instruction Itineraries

[bugzilla-daemon at cs.uiuc.edu]

http://llvm.org/bugs/show_bug.cgi?id=2200

           Summary: Wrong generation of multi-stage Instruction Itineraries
           Product: tools
           Version: 2.2
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Keywords: miscompilation
          Severity: blocker
          Priority: P2
         Component: TableGen
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: giuma.cordes at gmail.com
                CC: llvmbugs at cs.uiuc.edu


Created an attachment (id=1578)
 --> (http://llvm.org/bugs/attachment.cgi?id=1578)
SubtargetEmitter.cpp

Using the following description of InstrItineraries:

/////////////////////////////////////////////////////
include "Target.td"

def IALUS1  : FuncUnit;  // Integer ALU stage 1 
def IALUS2  : FuncUnit;  // Integer ALU stage 2

def LSUS1   : FuncUnit;  // Load/Store stage 1
def LSUS2   : FuncUnit;  // Load/Store stage 2
def LSUS3   : FuncUnit;  // Load/Store stage 3

def IntAlu2     : InstrItinClass;
def LdSt        : InstrItinClass;

def ShSItinerariesV0 : ProcessorItineraries<[
  InstrItinData<IntAlu2,[InstrStage<1, [IALUS1]>,
                         InstrStage<1, [IALUS2]>
  ]>,
  InstrItinData<LdSt,   [InstrStage<1, [LSUS1]>,
                         InstrStage<1, [LSUS2]>,
                         InstrStage<1, [LSUS3]>
  ]>
]>;

def T : Target {
}
/////////////////////////////////////////////////////

tblgen generates wrong itineraries

command:  $(LLVM_BIN)/tblgen  -gen-subtarget -I$(LLVM_SRC)/lib/Target/
-I$(LLVM_SRC)/include bug.td

output:

/////////////////////////////////////////////////////
static llvm::InstrStage Stages[] = {
  { 0, 0 }, // No itinerary
  { 1, IALUS1 },   { 1, IALUS2 }, // 1
  { 1, LSUS1 },   { 1, LSUS2 },   { 1, LSUS3 }, // 2
  { 0, 0 } // End itinerary
};

enum {
  StagesSize = sizeof(Stages)/sizeof(llvm::InstrStage)
};

static llvm::InstrItinerary TItinerariesV0[] = {
  { 1, 3 }, // 0
  { 2, 5 }, // 1
  { 0, 0 } // 2
};
/////////////////////////////////////////////////////

the range { 2, 5 } in TItinerariesV0[] for itinerary #1 clearly refers to the
wrong interval in the Stages array.
The correct range should be { 3, 6 }.


The problem is in in utils/TableGen/SubtargetEmitter.cpp, in function
SubtargetEmitter::EmitStageData, line 349:

      if (Find == 0) {
        // Emit as { cycles, u1 | u2 | ... | un }, // index
        OS << ItinString << ", // " << ItinEnum << "\n";
        // Record Itin class number
HERE!!  ItinMap[ItinString] = Find = ItinEnum++;  <--- bug HERE!!
      }

Indeed, this doesn't work for multi-stage itineraries, as ItinEnum gets
incremented by one, independently on the number of stages.

In attachment I propose a simple fix which takes indeed into account the
correct number of stages.

Thanks.


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