[llvm-mca] Report the number of dispatched micro opcodes in the DispatchStatistics view.

This patch introduces the following changes to the DispatchStatistics view:
 * DispatchStatistics now reports the number of dispatched opcodes instead of
   the number of dispatched instructions.
 * The "Dynamic Dispatch Stall Cycles" table now also reports the percentage of
   stall cycles against the total simulated cycles.

This change allows users to easily compare dispatch group sizes with the
processor DispatchWidth.
Before this change, it was difficult to correlate the two numbers, since
DispatchStatistics view reported numbers of instructions (instead of opcodes).
DispatchWidth defines the maximum size of a dispatch group in terms of number of
micro opcodes.

The other change introduced by this patch is related to how DispatchStage
generates "instruction dispatch" events.
In particular:
 * There can be multiple dispatch events associated with a same instruction
 * Each dispatch event now encapsulates the number of dispatched micro opcodes.

The number of micro opcodes declared by an instruction may exceed the processor
DispatchWidth. Therefore, we cannot assume that instructions are always fully
dispatched in a single cycle.
DispatchStage knows already how to handle instructions declaring a number of
opcodes bigger that DispatchWidth. However, DispatchStage always emitted a
single instruction dispatch event (during the first simulated dispatch cycle)
for instructions dispatched.

With this patch, DispatchStage now correctly notifies multiple dispatch events
for instructions that cannot be dispatched in a single cycle.

A few views had to be modified. Views can no longer assume that there can only
be one dispatch event per instruction.

Tests (and docs) have been updated.

Differential Revision: https://reviews.llvm.org/D51430


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@341055 91177308-0d34-0410-b5e6-96231b3b80d8

docs/CommandGuide/llvm-mca.rst

@@ -479,13 +479,13 @@ sections.
   Dynamic Dispatch Stall Cycles:
   RAT     - Register unavailable:                      0
   RCU     - Retire tokens unavailable:                 0
-  SCHEDQ  - Scheduler full:                            272
+  SCHEDQ  - Scheduler full:                            272  (44.6%)
   LQ      - Load queue full:                           0
   SQ      - Store queue full:                          0
   GROUP   - Static restrictions on the dispatch group: 0
 
 
-  Dispatch Logic - number of cycles where we saw N instructions dispatched:
+  Dispatch Logic - number of cycles where we saw N micro opcodes dispatched:
   [# dispatched], [# cycles]
    0,              24  (3.9%)
    1,              272  (44.6%)
@@ -533,12 +533,11 @@ sections.
 
 If we look at the *Dynamic Dispatch Stall Cycles* table, we see the counter for
 SCHEDQ reports 272 cycles.  This counter is incremented every time the dispatch
-logic is unable to dispatch a group of two instructions because the scheduler's
-queue is full.
+logic is unable to dispatch a full group because the scheduler's queue is full.
 
 Looking at the *Dispatch Logic* table, we see that the pipeline was only able to
-dispatch two instructions 51.5% of the time.  The dispatch group was limited to
-one instruction 44.6% of the cycles, which corresponds to 272 cycles.  The
+dispatch two micro opcodes 51.5% of the time.  The dispatch group was limited to
+one micro opcode 44.6% of the cycles, which corresponds to 272 cycles.  The
 dispatch statistics are displayed by either using the command option
 ``-all-stats`` or ``-dispatch-stats``.
 

test/tools/llvm-mca/X86/BtVer2/register-files-1.s

@@ -22,7 +22,7 @@ vmulps %xmm0, %xmm0, %xmm0
 # CHECK-NEXT: SQ      - Store queue full:                          0
 # CHECK-NEXT: GROUP   - Static restrictions on the dispatch group: 0
 
-# CHECK:      Dispatch Logic - number of cycles where we saw N instructions dispatched:
+# CHECK:      Dispatch Logic - number of cycles where we saw N micro opcodes dispatched:
 # CHECK-NEXT: [# dispatched], [# cycles]
 # CHECK-NEXT:  0,              23  (82.1%)
 # CHECK-NEXT:  2,              5  (17.9%)

test/tools/llvm-mca/X86/BtVer2/register-files-2.s

@@ -15,14 +15,14 @@ vmulps %xmm0, %xmm0, %xmm0
 # CHECK-NEXT: Block RThroughput: 1.0
 
 # CHECK:      Dynamic Dispatch Stall Cycles:
-# CHECK-NEXT: RAT     - Register unavailable:                      13
+# CHECK-NEXT: RAT     - Register unavailable:                      13  (46.4%)
 # CHECK-NEXT: RCU     - Retire tokens unavailable:                 0
 # CHECK-NEXT: SCHEDQ  - Scheduler full:                            0
 # CHECK-NEXT: LQ      - Load queue full:                           0
 # CHECK-NEXT: SQ      - Store queue full:                          0
 # CHECK-NEXT: GROUP   - Static restrictions on the dispatch group: 0
 
-# CHECK:      Dispatch Logic - number of cycles where we saw N instructions dispatched:
+# CHECK:      Dispatch Logic - number of cycles where we saw N micro opcodes dispatched:
 # CHECK-NEXT: [# dispatched], [# cycles]
 # CHECK-NEXT:  0,              20  (71.4%)
 # CHECK-NEXT:  1,              6  (21.4%)

test/tools/llvm-mca/X86/BtVer2/register-files-3.s

@@ -25,17 +25,17 @@ idiv %eax
 # CHECK-NEXT:  2      25    25.00                 U     idivl	%eax
 
 # CHECK:      Dynamic Dispatch Stall Cycles:
-# CHECK-NEXT: RAT     - Register unavailable:                      26
+# CHECK-NEXT: RAT     - Register unavailable:                      26  (47.3%)
 # CHECK-NEXT: RCU     - Retire tokens unavailable:                 0
 # CHECK-NEXT: SCHEDQ  - Scheduler full:                            0
 # CHECK-NEXT: LQ      - Load queue full:                           0
 # CHECK-NEXT: SQ      - Store queue full:                          0
 # CHECK-NEXT: GROUP   - Static restrictions on the dispatch group: 0
 
-# CHECK:      Dispatch Logic - number of cycles where we saw N instructions dispatched:
+# CHECK:      Dispatch Logic - number of cycles where we saw N micro opcodes dispatched:
 # CHECK-NEXT: [# dispatched], [# cycles]
 # CHECK-NEXT:  0,              53  (96.4%)
-# CHECK-NEXT:  1,              2  (3.6%)
+# CHECK-NEXT:  2,              2  (3.6%)
 
 # CHECK:      Register File statistics:
 # CHECK-NEXT: Total number of mappings created:    6

test/tools/llvm-mca/X86/BtVer2/register-files-4.s

@@ -25,17 +25,17 @@ idiv %eax
 # CHECK-NEXT:  2      25    25.00                 U     idivl	%eax
 
 # CHECK:      Dynamic Dispatch Stall Cycles:
-# CHECK-NEXT: RAT     - Register unavailable:                      6
+# CHECK-NEXT: RAT     - Register unavailable:                      6  (1.1%)
 # CHECK-NEXT: RCU     - Retire tokens unavailable:                 0
 # CHECK-NEXT: SCHEDQ  - Scheduler full:                            0
 # CHECK-NEXT: LQ      - Load queue full:                           0
 # CHECK-NEXT: SQ      - Store queue full:                          0
 # CHECK-NEXT: GROUP   - Static restrictions on the dispatch group: 0
 
-# CHECK:      Dispatch Logic - number of cycles where we saw N instructions dispatched:
+# CHECK:      Dispatch Logic - number of cycles where we saw N micro opcodes dispatched:
 # CHECK-NEXT: [# dispatched], [# cycles]
 # CHECK-NEXT:  0,              531  (96.0%)
-# CHECK-NEXT:  1,              22  (4.0%)
+# CHECK-NEXT:  2,              22  (4.0%)
 
 # CHECK:      Register File statistics:
 # CHECK-NEXT: Total number of mappings created:    66

test/tools/llvm-mca/X86/BtVer2/register-files-5.s

@@ -47,16 +47,16 @@
 
 # CHECK:      Dynamic Dispatch Stall Cycles:
 # CHECK-NEXT: RAT     - Register unavailable:                      0
-# CHECK-NEXT: RCU     - Retire tokens unavailable:                 8
+# CHECK-NEXT: RCU     - Retire tokens unavailable:                 8  (11.6%)
 # CHECK-NEXT: SCHEDQ  - Scheduler full:                            0
 # CHECK-NEXT: LQ      - Load queue full:                           0
 # CHECK-NEXT: SQ      - Store queue full:                          0
 # CHECK-NEXT: GROUP   - Static restrictions on the dispatch group: 0
 
-# CHECK:      Dispatch Logic - number of cycles where we saw N instructions dispatched:
+# CHECK:      Dispatch Logic - number of cycles where we saw N micro opcodes dispatched:
 # CHECK-NEXT: [# dispatched], [# cycles]
 # CHECK-NEXT:  0,              36  (52.2%)
-# CHECK-NEXT:  1,              33  (47.8%)
+# CHECK-NEXT:  2,              33  (47.8%)
 
 # CHECK:      Register File statistics:
 # CHECK-NEXT: Total number of mappings created:    66

test/tools/llvm-mca/X86/Haswell/cmpxchg16b.s

@@ -0,0 +1,76 @@
+# NOTE: Assertions have been autogenerated by utils/update_mca_test_checks.py
+# RUN: llvm-mca -mtriple=x86_64-unknown-unknown -mcpu=haswell -timeline -timeline-max-iterations=3 -dispatch-stats < %s | FileCheck %s
+
+cmpxchg16b (%rsi)
+
+# CHECK:      Iterations:        100
+# CHECK-NEXT: Instructions:      100
+# CHECK-NEXT: Total Cycles:      2203
+# CHECK-NEXT: Total uOps:        1900
+
+# CHECK:      Dispatch Width:    4
+# CHECK-NEXT: uOps Per Cycle:    0.86
+# CHECK-NEXT: IPC:               0.05
+# CHECK-NEXT: Block RThroughput: 4.8
+
+# CHECK:      Instruction Info:
+# CHECK-NEXT: [1]: #uOps
+# CHECK-NEXT: [2]: Latency
+# CHECK-NEXT: [3]: RThroughput
+# CHECK-NEXT: [4]: MayLoad
+# CHECK-NEXT: [5]: MayStore
+# CHECK-NEXT: [6]: HasSideEffects (U)
+
+# CHECK:      [1]    [2]    [3]    [4]    [5]    [6]    Instructions:
+# CHECK-NEXT:  19     22    4.00    *      *            cmpxchg16b	(%rsi)
+
+# CHECK:      Dynamic Dispatch Stall Cycles:
+# CHECK-NEXT: RAT     - Register unavailable:                      0
+# CHECK-NEXT: RCU     - Retire tokens unavailable:                 1487  (67.5%)
+# CHECK-NEXT: SCHEDQ  - Scheduler full:                            0
+# CHECK-NEXT: LQ      - Load queue full:                           0
+# CHECK-NEXT: SQ      - Store queue full:                          0
+# CHECK-NEXT: GROUP   - Static restrictions on the dispatch group: 0
+
+# CHECK:      Dispatch Logic - number of cycles where we saw N micro opcodes dispatched:
+# CHECK-NEXT: [# dispatched], [# cycles]
+# CHECK-NEXT:  0,              1703  (77.3%)
+# CHECK-NEXT:  3,              100  (4.5%)
+# CHECK-NEXT:  4,              400  (18.2%)
+
+# CHECK:      Resources:
+# CHECK-NEXT: [0]   - HWDivider
+# CHECK-NEXT: [1]   - HWFPDivider
+# CHECK-NEXT: [2]   - HWPort0
+# CHECK-NEXT: [3]   - HWPort1
+# CHECK-NEXT: [4]   - HWPort2
+# CHECK-NEXT: [5]   - HWPort3
+# CHECK-NEXT: [6]   - HWPort4
+# CHECK-NEXT: [7]   - HWPort5
+# CHECK-NEXT: [8]   - HWPort6
+# CHECK-NEXT: [9]   - HWPort7
+
+# CHECK:      Resource pressure per iteration:
+# CHECK-NEXT: [0]    [1]    [2]    [3]    [4]    [5]    [6]    [7]    [8]    [9]
+# CHECK-NEXT:  -      -     2.00   6.00   0.66   0.67   1.00   4.00   4.00   0.67
+
+# CHECK:      Resource pressure by instruction:
+# CHECK-NEXT: [0]    [1]    [2]    [3]    [4]    [5]    [6]    [7]    [8]    [9]    Instructions:
+# CHECK-NEXT:  -      -     2.00   6.00   0.66   0.67   1.00   4.00   4.00   0.67   cmpxchg16b	(%rsi)
+
+# CHECK:      Timeline view:
+# CHECK-NEXT:                     0123456789          0123456789          0123456789
+# CHECK-NEXT: Index     0123456789          0123456789          0123456789          012345678
+
+# CHECK:      [0,0]     DeeeeeeeeeeeeeeeeeeeeeeER.    .    .    .    .    .    .    .    .  .   cmpxchg16b	(%rsi)
+# CHECK-NEXT: [1,0]     .    D=================eeeeeeeeeeeeeeeeeeeeeeER   .    .    .    .  .   cmpxchg16b	(%rsi)
+# CHECK-NEXT: [2,0]     .    .    D==================================eeeeeeeeeeeeeeeeeeeeeeER   cmpxchg16b	(%rsi)
+
+# CHECK:      Average Wait times (based on the timeline view):
+# CHECK-NEXT: [0]: Executions
+# CHECK-NEXT: [1]: Average time spent waiting in a scheduler's queue
+# CHECK-NEXT: [2]: Average time spent waiting in a scheduler's queue while ready
+# CHECK-NEXT: [3]: Average time elapsed from WB until retire stage
+
+# CHECK:            [0]    [1]    [2]    [3]
+# CHECK-NEXT: 0.     3     18.0   0.3    0.0       cmpxchg16b	(%rsi)

test/tools/llvm-mca/X86/option-all-stats-1.s

@@ -30,12 +30,12 @@ add %eax, %eax
 # FULLREPORT:      Dynamic Dispatch Stall Cycles:
 # FULLREPORT-NEXT: RAT     - Register unavailable:                      0
 # FULLREPORT-NEXT: RCU     - Retire tokens unavailable:                 0
-# FULLREPORT-NEXT: SCHEDQ  - Scheduler full:                            61
+# FULLREPORT-NEXT: SCHEDQ  - Scheduler full:                            61  (59.2%)
 # FULLREPORT-NEXT: LQ      - Load queue full:                           0
 # FULLREPORT-NEXT: SQ      - Store queue full:                          0
 # FULLREPORT-NEXT: GROUP   - Static restrictions on the dispatch group: 0
 
-# FULLREPORT:      Dispatch Logic - number of cycles where we saw N instructions dispatched:
+# FULLREPORT:      Dispatch Logic - number of cycles where we saw N micro opcodes dispatched:
 # FULLREPORT-NEXT: [# dispatched], [# cycles]
 # FULLREPORT-NEXT:  0,              22  (21.4%)
 # FULLREPORT-NEXT:  1,              62  (60.2%)

test/tools/llvm-mca/X86/option-all-stats-2.s

@@ -31,12 +31,12 @@ add %eax, %eax
 # FULL:      Dynamic Dispatch Stall Cycles:
 # FULL-NEXT: RAT     - Register unavailable:                      0
 # FULL-NEXT: RCU     - Retire tokens unavailable:                 0
-# FULL-NEXT: SCHEDQ  - Scheduler full:                            61
+# FULL-NEXT: SCHEDQ  - Scheduler full:                            61  (59.2%)
 # FULL-NEXT: LQ      - Load queue full:                           0
 # FULL-NEXT: SQ      - Store queue full:                          0
 # FULL-NEXT: GROUP   - Static restrictions on the dispatch group: 0
 
-# FULL:      Dispatch Logic - number of cycles where we saw N instructions dispatched:
+# FULL:      Dispatch Logic - number of cycles where we saw N micro opcodes dispatched:
 # FULL-NEXT: [# dispatched], [# cycles]
 # FULL-NEXT:  0,              22  (21.4%)
 # FULL-NEXT:  1,              62  (60.2%)

test/tools/llvm-mca/X86/option-all-views-1.s

@@ -32,12 +32,12 @@ add %eax, %eax
 # FULLREPORT:         Dynamic Dispatch Stall Cycles:
 # FULLREPORT-NEXT:    RAT     - Register unavailable:                      0
 # FULLREPORT-NEXT:    RCU     - Retire tokens unavailable:                 0
-# FULLREPORT-NEXT:    SCHEDQ  - Scheduler full:                            61
+# FULLREPORT-NEXT:    SCHEDQ  - Scheduler full:                            61  (59.2%)
 # FULLREPORT-NEXT:    LQ      - Load queue full:                           0
 # FULLREPORT-NEXT:    SQ      - Store queue full:                          0
 # FULLREPORT-NEXT:    GROUP   - Static restrictions on the dispatch group: 0
 
-# FULLREPORT:         Dispatch Logic - number of cycles where we saw N instructions dispatched:
+# FULLREPORT:         Dispatch Logic - number of cycles where we saw N micro opcodes dispatched:
 # FULLREPORT-NEXT:    [# dispatched], [# cycles]
 # FULLREPORT-NEXT:     0,              22  (21.4%)
 # FULLREPORT-NEXT:     1,              62  (60.2%)

test/tools/llvm-mca/X86/option-all-views-2.s

@@ -31,12 +31,12 @@ add %eax, %eax
 # ALL:             Dynamic Dispatch Stall Cycles:
 # ALL-NEXT:        RAT     - Register unavailable:                      0
 # ALL-NEXT:        RCU     - Retire tokens unavailable:                 0
-# ALL-NEXT:        SCHEDQ  - Scheduler full:                            61
+# ALL-NEXT:        SCHEDQ  - Scheduler full:                            61  (59.2%)
 # ALL-NEXT:        LQ      - Load queue full:                           0
 # ALL-NEXT:        SQ      - Store queue full:                          0
 # ALL-NEXT:        GROUP   - Static restrictions on the dispatch group: 0
 
-# ALL:             Dispatch Logic - number of cycles where we saw N instructions dispatched:
+# ALL:             Dispatch Logic - number of cycles where we saw N micro opcodes dispatched:
 # ALL-NEXT:        [# dispatched], [# cycles]
 # ALL-NEXT:         0,              22  (21.4%)
 # ALL-NEXT:         1,              62  (60.2%)

tools/llvm-mca/Views/DispatchStatistics.cpp

@@ -26,20 +26,23 @@ void DispatchStatistics::onEvent(const HWStallEvent &Event) {
 }
 
 void DispatchStatistics::onEvent(const HWInstructionEvent &Event) {
-  if (Event.Type == HWInstructionEvent::Dispatched)
-    ++NumDispatched;
+  if (Event.Type != HWInstructionEvent::Dispatched)
+    return;
+
+  const auto &DE = static_cast<const HWInstructionDispatchedEvent &>(Event);
+  NumDispatched += DE.MicroOpcodes;
 }
 
 void DispatchStatistics::printDispatchHistogram(llvm::raw_ostream &OS) const {
   std::string Buffer;
   raw_string_ostream TempStream(Buffer);
   TempStream << "\n\nDispatch Logic - "
-             << "number of cycles where we saw N instructions dispatched:\n";
+             << "number of cycles where we saw N micro opcodes dispatched:\n";
   TempStream << "[# dispatched], [# cycles]\n";
   for (const std::pair<unsigned, unsigned> &Entry : DispatchGroupSizePerCycle) {
+    double Percentage = ((double)Entry.second / NumCycles) * 100.0;
     TempStream << " " << Entry.first << ",              " << Entry.second
-               << "  ("
-               << format("%.1f", ((double)Entry.second / NumCycles) * 100.0)
+               << "  (" << format("%.1f", floor((Percentage * 10) + 0.5) / 10)
                << "%)\n";
   }
 
@@ -47,24 +50,36 @@ void DispatchStatistics::printDispatchHistogram(llvm::raw_ostream &OS) const {
   OS << Buffer;
 }
 
+static void printStalls(raw_ostream &OS, unsigned NumStalls,
+                        unsigned NumCycles) {
+  if (!NumStalls) {
+    OS << NumStalls;
+    return;
+  }
+
+  double Percentage = ((double)NumStalls / NumCycles) * 100.0;
+  OS << NumStalls << "  ("
+     << format("%.1f", floor((Percentage * 10) + 0.5) / 10) << "%)";
+}
+
 void DispatchStatistics::printDispatchStalls(raw_ostream &OS) const {
   std::string Buffer;
-  raw_string_ostream TempStream(Buffer);
-  TempStream << "\n\nDynamic Dispatch Stall Cycles:\n";
-  TempStream << "RAT     - Register unavailable:                      "
-             << HWStalls[HWStallEvent::RegisterFileStall];
-  TempStream << "\nRCU     - Retire tokens unavailable:                 "
-             << HWStalls[HWStallEvent::RetireControlUnitStall];
-  TempStream << "\nSCHEDQ  - Scheduler full:                            "
-             << HWStalls[HWStallEvent::SchedulerQueueFull];
-  TempStream << "\nLQ      - Load queue full:                           "
-             << HWStalls[HWStallEvent::LoadQueueFull];
-  TempStream << "\nSQ      - Store queue full:                          "
-             << HWStalls[HWStallEvent::StoreQueueFull];
-  TempStream << "\nGROUP   - Static restrictions on the dispatch group: "
-             << HWStalls[HWStallEvent::DispatchGroupStall];
-  TempStream << '\n';
-  TempStream.flush();
+  raw_string_ostream SS(Buffer);
+  SS << "\n\nDynamic Dispatch Stall Cycles:\n";
+  SS << "RAT     - Register unavailable:                      ";
+  printStalls(SS, HWStalls[HWStallEvent::RegisterFileStall], NumCycles);
+  SS << "\nRCU     - Retire tokens unavailable:                 ";
+  printStalls(SS, HWStalls[HWStallEvent::RetireControlUnitStall], NumCycles);
+  SS << "\nSCHEDQ  - Scheduler full:                            ";
+  printStalls(SS, HWStalls[HWStallEvent::SchedulerQueueFull], NumCycles);
+  SS << "\nLQ      - Load queue full:                           ";
+  printStalls(SS, HWStalls[HWStallEvent::LoadQueueFull], NumCycles);
+  SS << "\nSQ      - Store queue full:                          ";
+  printStalls(SS, HWStalls[HWStallEvent::StoreQueueFull], NumCycles);
+  SS << "\nGROUP   - Static restrictions on the dispatch group: ";
+  printStalls(SS, HWStalls[HWStallEvent::DispatchGroupStall], NumCycles);
+  SS << '\n';
+  SS.flush();
   OS << Buffer;
 }
 

tools/llvm-mca/Views/DispatchStatistics.h

@@ -24,7 +24,7 @@
 /// GROUP   - Static restrictions on the dispatch group: 0
 ///
 ///
-/// Dispatch Logic - number of cycles where we saw N instructions dispatched:
+/// Dispatch Logic - number of cycles where we saw N micro opcodes dispatched:
 /// [# dispatched], [# cycles]
 ///  0,              15  (11.5%)
 ///  2,              4  (3.1%)

tools/llvm-mca/Views/SummaryView.cpp

@@ -33,12 +33,10 @@ SummaryView::SummaryView(const llvm::MCSchedModel &Model, const SourceMgr &S,
 }
 
 void SummaryView::onEvent(const HWInstructionEvent &Event) {
-  // We are only interested in the "instruction dispatched" events generated by
-  // the dispatch stage for instructions that are part of iteration #0.
-  if (Event.Type != HWInstructionEvent::Dispatched)
-    return;
-
-  if (Event.IR.getSourceIndex() >= Source.size())
+  // We are only interested in the "instruction retired" events generated by
+  // the retire stage for instructions that are part of iteration #0.
+  if (Event.Type != HWInstructionEvent::Retired ||
+      Event.IR.getSourceIndex() >= Source.size())
     return;
 
   // Update the cumulative number of resource cycles based on the processor

tools/llvm-mca/Views/TimelineView.cpp

@@ -29,6 +29,8 @@ TimelineView::TimelineView(const MCSubtargetInfo &sti, MCInstPrinter &Printer,
     MaxIterations = DEFAULT_ITERATIONS;
   NumInstructions *= std::min(MaxIterations, AsmSequence.getNumIterations());
   Timeline.resize(NumInstructions);
+  TimelineViewEntry InvalidTVEntry = {-1, 0, 0, 0};
+  std::fill(Timeline.begin(), Timeline.end(), InvalidTVEntry);
 
   WaitTimeEntry NullWTEntry = {0, 0, 0};
   std::fill(WaitTime.begin(), WaitTime.end(), NullWTEntry);
@@ -68,10 +70,13 @@ void TimelineView::onEvent(const HWInstructionEvent &Event) {
       TVEntry.CycleRetired = CurrentCycle;
 
     // Update the WaitTime entry which corresponds to this Index.
+    assert(TVEntry.CycleDispatched >= 0 && "Invalid TVEntry found!");
+    unsigned CycleDispatched = static_cast<unsigned>(TVEntry.CycleDispatched);
     WaitTimeEntry &WTEntry = WaitTime[Index % AsmSequence.size()];
     WTEntry.CyclesSpentInSchedulerQueue +=
-        TVEntry.CycleIssued - TVEntry.CycleDispatched;
-    assert(TVEntry.CycleDispatched <= TVEntry.CycleReady);
+        TVEntry.CycleIssued - CycleDispatched;
+    assert(CycleDispatched <= TVEntry.CycleReady &&
+           "Instruction cannot be ready if it hasn't been dispatched yet!");
     WTEntry.CyclesSpentInSQWhileReady +=
         TVEntry.CycleIssued - TVEntry.CycleReady;
     WTEntry.CyclesSpentAfterWBAndBeforeRetire +=
@@ -88,7 +93,11 @@ void TimelineView::onEvent(const HWInstructionEvent &Event) {
     Timeline[Index].CycleExecuted = CurrentCycle;
     break;
   case HWInstructionEvent::Dispatched:
-    Timeline[Index].CycleDispatched = CurrentCycle;
+    // There may be multiple dispatch events. Microcoded instructions that are
+    // expanded into multiple uOps may require multiple dispatch cycles. Here,
+    // we want to capture the first dispatch cycle.
+    if (Timeline[Index].CycleDispatched == -1)
+      Timeline[Index].CycleDispatched = static_cast<int>(CurrentCycle);
     break;
   default:
     return;
@@ -193,19 +202,20 @@ void TimelineView::printTimelineViewEntry(formatted_raw_ostream &OS,
     OS << '\n';
   OS << '[' << Iteration << ',' << SourceIndex << ']';
   OS.PadToColumn(10);
-  for (unsigned I = 0, E = Entry.CycleDispatched; I < E; ++I)
+  assert(Entry.CycleDispatched >= 0 && "Invalid TimelineViewEntry!");
+  unsigned CycleDispatched = static_cast<unsigned>(Entry.CycleDispatched);
+  for (unsigned I = 0, E = CycleDispatched; I < E; ++I)
     OS << ((I % 5 == 0) ? '.' : ' ');
   OS << TimelineView::DisplayChar::Dispatched;
-  if (Entry.CycleDispatched != Entry.CycleExecuted) {
+  if (CycleDispatched != Entry.CycleExecuted) {
     // Zero latency instructions have the same value for CycleDispatched,
     // CycleIssued and CycleExecuted.
-    for (unsigned I = Entry.CycleDispatched + 1, E = Entry.CycleIssued; I < E;
-         ++I)
+    for (unsigned I = CycleDispatched + 1, E = Entry.CycleIssued; I < E; ++I)
       OS << TimelineView::DisplayChar::Waiting;
     if (Entry.CycleIssued == Entry.CycleExecuted)
       OS << TimelineView::DisplayChar::DisplayChar::Executed;
     else {
-      if (Entry.CycleDispatched != Entry.CycleIssued)
+      if (CycleDispatched != Entry.CycleIssued)
         OS << TimelineView::DisplayChar::Executing;
       for (unsigned I = Entry.CycleIssued + 1, E = Entry.CycleExecuted; I < E;
            ++I)

tools/llvm-mca/Views/TimelineView.h

@@ -126,7 +126,7 @@ class TimelineView : public View {
   unsigned LastCycle;
 
   struct TimelineViewEntry {
-    unsigned CycleDispatched;
+    int CycleDispatched;  // A negative value is an "invalid cycle".
     unsigned CycleReady;
     unsigned CycleIssued;
     unsigned CycleExecuted;

tools/llvm-mca/include/HWEventListener.h

@@ -70,12 +70,23 @@ public:
 
 class HWInstructionDispatchedEvent : public HWInstructionEvent {
 public:
-  HWInstructionDispatchedEvent(const InstRef &IR, llvm::ArrayRef<unsigned> Regs)
+  HWInstructionDispatchedEvent(const InstRef &IR, llvm::ArrayRef<unsigned> Regs,
+                               unsigned UOps)
       : HWInstructionEvent(HWInstructionEvent::Dispatched, IR),
-        UsedPhysRegs(Regs) {}
+        UsedPhysRegs(Regs), MicroOpcodes(UOps) {}
   // Number of physical register allocated for this instruction. There is one
   // entry per register file.
   llvm::ArrayRef<unsigned> UsedPhysRegs;
+  // Number of micro opcodes dispatched.
+  // This field is often set to the total number of micro-opcodes specified by
+  // the instruction descriptor of IR.
+  // The only exception is when IR declares a number of micro opcodes
+  // which exceeds the processor DispatchWidth, and - by construction - it
+  // requires multiple cycles to be fully dispatched. In that particular case,
+  // the dispatch logic would generate more than one dispatch event (one per
+  // cycle), and each event would declare how many micro opcodes are effectively
+  // been dispatched to the schedulers.
+  unsigned MicroOpcodes;
 };
 
 class HWInstructionRetiredEvent : public HWInstructionEvent {

tools/llvm-mca/include/Stages/DispatchStage.h

@@ -51,6 +51,7 @@ class DispatchStage final : public Stage {
   unsigned DispatchWidth;
   unsigned AvailableEntries;
   unsigned CarryOver;
+  InstRef CarriedOver;
   const llvm::MCSubtargetInfo &STI;
   RetireControlUnit &RCU;
   RegisterFile &PRF;
@@ -63,7 +64,8 @@ class DispatchStage final : public Stage {
   void updateRAWDependencies(ReadState &RS, const llvm::MCSubtargetInfo &STI);
 
   void notifyInstructionDispatched(const InstRef &IR,
-                                   llvm::ArrayRef<unsigned> UsedPhysRegs);
+                                   llvm::ArrayRef<unsigned> UsedPhysRegs,
+                                   unsigned uOps);
 
   void collectWrites(llvm::SmallVectorImpl<WriteRef> &Vec,
                      unsigned RegID) const {
@@ -75,7 +77,7 @@ public:
                 const llvm::MCRegisterInfo &MRI, unsigned MaxDispatchWidth,
                 RetireControlUnit &R, RegisterFile &F)
       : DispatchWidth(MaxDispatchWidth), AvailableEntries(MaxDispatchWidth),
-        CarryOver(0U), STI(Subtarget), RCU(R), PRF(F) {}
+        CarryOver(0U), CarriedOver(), STI(Subtarget), RCU(R), PRF(F) {}
 
   bool isAvailable(const InstRef &IR) const override;
 

tools/llvm-mca/lib/Stages/DispatchStage.cpp

@@ -28,9 +28,11 @@ using namespace llvm;
 namespace mca {
 
 void DispatchStage::notifyInstructionDispatched(const InstRef &IR,
-                                                ArrayRef<unsigned> UsedRegs) {
+                                                ArrayRef<unsigned> UsedRegs,
+                                                unsigned UOps) {
   LLVM_DEBUG(dbgs() << "[E] Instruction Dispatched: #" << IR << '\n');
-  notifyEvent<HWInstructionEvent>(HWInstructionDispatchedEvent(IR, UsedRegs));
+  notifyEvent<HWInstructionEvent>(
+      HWInstructionDispatchedEvent(IR, UsedRegs, UOps));
 }
 
 bool DispatchStage::checkPRF(const InstRef &IR) const {
@@ -92,6 +94,7 @@ llvm::Error DispatchStage::dispatch(InstRef IR) {
     assert(AvailableEntries == DispatchWidth);
     AvailableEntries = 0;
     CarryOver = NumMicroOps - DispatchWidth;
+    CarriedOver = IR;
   } else {
     assert(AvailableEntries >= NumMicroOps);
     AvailableEntries -= NumMicroOps;
@@ -125,13 +128,26 @@ llvm::Error DispatchStage::dispatch(InstRef IR) {
 
   // Notify listeners of the "instruction dispatched" event,
   // and move IR to the next stage.
-  notifyInstructionDispatched(IR, RegisterFiles);
+  notifyInstructionDispatched(IR, RegisterFiles,
+                              std::min(DispatchWidth, NumMicroOps));
   return moveToTheNextStage(IR);
 }
 
 llvm::Error DispatchStage::cycleStart() {
+  if (!CarryOver) {
+    AvailableEntries = DispatchWidth;
+    return llvm::ErrorSuccess();
+  }
+
   AvailableEntries = CarryOver >= DispatchWidth ? 0 : DispatchWidth - CarryOver;
-  CarryOver = CarryOver >= DispatchWidth ? CarryOver - DispatchWidth : 0U;
+  unsigned DispatchedOpcodes = DispatchWidth - AvailableEntries;
+  CarryOver -= DispatchedOpcodes;
+  assert(CarriedOver.isValid() && "Invalid dispatched instruction");
+  
+  SmallVector<unsigned, 8> RegisterFiles(PRF.getNumRegisterFiles(), 0U);
+  notifyInstructionDispatched(CarriedOver, RegisterFiles, DispatchedOpcodes);
+  if (!CarryOver)
+    CarriedOver = InstRef();
   return llvm::ErrorSuccess();
 }