[llvm] r331193 - [llvm-mca] Correctly handle zero-latency stores that consume pipeline resources.

[Andrea Di Biagio via llvm-commits]

Author: adibiagio
Date: Mon Apr 30 08:55:04 2018
New Revision: 331193

URL: http://llvm.org/viewvc/llvm-project?rev=331193&view=rev
Log:
[llvm-mca] Correctly handle zero-latency stores that consume pipeline resources.

This fixes PR37293.

We can have scheduling classes with no write latency entries, that still consume
processor resources. We don't want to treat those instructions as zero-latency
instructions; they still have to be issued to the underlying pipelines, so they
still consume resource cycles.

This is likely to be a regression which I have accidentally introduced at
revision 330807. Now, if an instruction has a non-empty set of write processor
resources, we conservatively treat it as a normal (i.e. non zero-latency)
instruction.

Added:
    llvm/trunk/test/tools/llvm-mca/AArch64/Falkor/
    llvm/trunk/test/tools/llvm-mca/AArch64/Falkor/zero-latency-store.s
Modified:
    llvm/trunk/tools/llvm-mca/Dispatch.cpp
    llvm/trunk/tools/llvm-mca/Scheduler.cpp

Added: llvm/trunk/test/tools/llvm-mca/AArch64/Falkor/zero-latency-store.s
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/tools/llvm-mca/AArch64/Falkor/zero-latency-store.s?rev=331193&view=auto
==============================================================================
--- llvm/trunk/test/tools/llvm-mca/AArch64/Falkor/zero-latency-store.s (added)
+++ llvm/trunk/test/tools/llvm-mca/AArch64/Falkor/zero-latency-store.s Mon Apr 30 08:55:04 2018
@@ -0,0 +1,44 @@
+# NOTE: Assertions have been autogenerated by utils/update_mca_test_checks.py
+# RUN: llvm-mca -march=aarch64 -mcpu=falkor -iterations=2 < %s | FileCheck %s
+
+  stp	d0, d1, [x0]
+
+# CHECK:      Iterations:     2
+# CHECK-NEXT: Instructions:   2
+# CHECK-NEXT: Total Cycles:   4
+# CHECK-NEXT: Dispatch Width: 8
+# CHECK-NEXT: IPC:            0.50
+
+# 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
+
+# CHECK:      [1]    [2]    [3]    [4]    [5]    [6]	Instructions:
+# CHECK-NEXT:  2      0     1.00           *        	stp	d0, d1, [x0]
+
+# CHECK:      Resources:
+# CHECK-NEXT: [0] - FalkorUnitB
+# CHECK-NEXT: [1] - FalkorUnitGTOV
+# CHECK-NEXT: [2] - FalkorUnitLD
+# CHECK-NEXT: [3] - FalkorUnitSD
+# CHECK-NEXT: [4] - FalkorUnitST
+# CHECK-NEXT: [5] - FalkorUnitVSD
+# CHECK-NEXT: [6] - FalkorUnitVTOG
+# CHECK-NEXT: [7] - FalkorUnitVX
+# CHECK-NEXT: [8] - FalkorUnitVY
+# CHECK-NEXT: [9] - FalkorUnitX
+# CHECK-NEXT: [10] - FalkorUnitY
+# CHECK-NEXT: [11] - FalkorUnitZ
+
+# CHECK:      Resource pressure per iteration:
+# CHECK-NEXT: [0]    [1]    [2]    [3]    [4]    [5]    [6]    [7]    [8]    [9]    [10]   [11]
+# CHECK-NEXT:  -      -      -      -     1.00   1.00    -      -      -      -      -      -
+
+# CHECK:      Resource pressure by instruction:
+# CHECK-NEXT: [0]    [1]    [2]    [3]    [4]    [5]    [6]    [7]    [8]    [9]    [10]   [11]   	Instructions:
+# CHECK-NEXT:  -      -      -      -     1.00   1.00    -      -      -      -      -      -     	stp	d0, d1, [x0]
+

Modified: llvm/trunk/tools/llvm-mca/Dispatch.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/tools/llvm-mca/Dispatch.cpp?rev=331193&r1=331192&r2=331193&view=diff
==============================================================================
--- llvm/trunk/tools/llvm-mca/Dispatch.cpp (original)
+++ llvm/trunk/tools/llvm-mca/Dispatch.cpp Mon Apr 30 08:55:04 2018
@@ -411,7 +411,8 @@ void DispatchUnit::dispatch(unsigned IID
   // instruction. The assumption is that a zero-latency instruction doesn't
   // require to be issued to the scheduler for execution. More importantly, it
   // doesn't have to wait on the register input operands.
-  if (NewInst->getDesc().MaxLatency)
+  const InstrDesc &Desc = NewInst->getDesc();
+  if (Desc.MaxLatency || !Desc.Resources.empty())
     for (std::unique_ptr<ReadState> &RS : NewInst->getUses())
       updateRAWDependencies(*RS, STI);
 

Modified: llvm/trunk/tools/llvm-mca/Scheduler.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/tools/llvm-mca/Scheduler.cpp?rev=331193&r1=331192&r2=331193&view=diff
==============================================================================
--- llvm/trunk/tools/llvm-mca/Scheduler.cpp (original)
+++ llvm/trunk/tools/llvm-mca/Scheduler.cpp Mon Apr 30 08:55:04 2018
@@ -258,12 +258,13 @@ void Scheduler::scheduleInstruction(unsi
   // targets, zero-idiom instructions (for example: a xor that clears the value
   // of a register) are treated speacially, and are often eliminated at register
   // renaming stage.
+  bool IsZeroLatency = !Desc.MaxLatency && Desc.Resources.empty();
 
   // Instructions that use an in-order dispatch/issue processor resource must be
   // issued immediately to the pipeline(s). Any other in-order buffered
   // resources (i.e. BufferSize=1) is consumed.
 
-  if (Desc.MaxLatency && !Resources->mustIssueImmediately(Desc)) {
+  if (!IsZeroLatency && !Resources->mustIssueImmediately(Desc)) {
     DEBUG(dbgs() << "[SCHEDULER] Adding " << Idx << " to the Ready Queue\n");
     ReadyQueue[Idx] = &MCIS;
     return;