[llvm] 90a9979 - [llvm][CodeGen] Fixed a bug in stall cycle calculation for window scheduler (#99451)

[via llvm-commits]

Author: Kai Yan
Date: 2024-07-25T19:16:23+08:00
New Revision: 90a997988279ecd0e9aefcf14ee0642093b03398

URL: https://github.com/llvm/llvm-project/commit/90a997988279ecd0e9aefcf14ee0642093b03398
DIFF: https://github.com/llvm/llvm-project/commit/90a997988279ecd0e9aefcf14ee0642093b03398.diff

LOG: [llvm][CodeGen] Fixed a bug in stall cycle calculation for window scheduler (#99451)

Fixed a bug in stall cycle calculation.
When a register defined by an instruction in the current iteration is
used by an instruction in the next iteration, we have modified the
number of stall cycle that need to be inserted.

Added: 
    llvm/test/CodeGen/Hexagon/swp-ws-stall-cycle.mir

Modified: 
    llvm/lib/CodeGen/WindowScheduler.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/CodeGen/WindowScheduler.cpp b/llvm/lib/CodeGen/WindowScheduler.cpp
index cb878f7425481..6a2c6537470db 100644
--- a/llvm/lib/CodeGen/WindowScheduler.cpp
+++ b/llvm/lib/CodeGen/WindowScheduler.cpp
@@ -492,6 +492,7 @@ int WindowScheduler::calculateMaxCycle(ScheduleDAGInstrs &DAG,
 // ========================================
 int WindowScheduler::calculateStallCycle(unsigned Offset, int MaxCycle) {
   int MaxStallCycle = 0;
+  int CurrentII = MaxCycle + 1;
   auto Range = getScheduleRange(Offset, SchedInstrNum);
   for (auto &MI : Range) {
     auto *SU = TripleDAG->getSUnit(&MI);
@@ -499,8 +500,8 @@ int WindowScheduler::calculateStallCycle(unsigned Offset, int MaxCycle) {
     for (auto &Succ : SU->Succs) {
       if (Succ.isWeak() || Succ.getSUnit() == &TripleDAG->ExitSU)
         continue;
-      // If the expected cycle does not exceed MaxCycle, no check is needed.
-      if (DefCycle + (int)Succ.getLatency() <= MaxCycle)
+      // If the expected cycle does not exceed CurrentII, no check is needed.
+      if (DefCycle + (int)Succ.getLatency() <= CurrentII)
         continue;
       // If the cycle of the scheduled MI A is less than that of the scheduled
       // MI B, the scheduling will fail because the lifetime of the
@@ -510,7 +511,7 @@ int WindowScheduler::calculateStallCycle(unsigned Offset, int MaxCycle) {
       if (DefCycle < UseCycle)
         return WindowIILimit;
       // Get the stall cycle introduced by the register between two trips.
-      int StallCycle = DefCycle + (int)Succ.getLatency() - MaxCycle - UseCycle;
+      int StallCycle = DefCycle + (int)Succ.getLatency() - CurrentII - UseCycle;
       MaxStallCycle = std::max(MaxStallCycle, StallCycle);
     }
   }

diff  --git a/llvm/test/CodeGen/Hexagon/swp-ws-stall-cycle.mir b/llvm/test/CodeGen/Hexagon/swp-ws-stall-cycle.mir
new file mode 100644
index 0000000000000..ddba67d78eb58
--- /dev/null
+++ b/llvm/test/CodeGen/Hexagon/swp-ws-stall-cycle.mir
@@ -0,0 +1,59 @@
+# REQUIRES: asserts
+# RUN: llc --march=hexagon %s -run-pass=pipeliner -debug-only=pipeliner \
+# RUN: -window-sched=force -filetype=null -verify-machineinstrs \
+# RUN: -window-region-limit=1 -window-search-ratio=100 -window-
diff -limit=0 \
+# RUN: 2>&1 | FileCheck %s
+
+# CHECK-LABEL: Start analyzing II
+# CHECK: MaxStallCycle is 0
+# CHECK-LABEL: Start analyzing II
+# CHECK: MaxStallCycle is 0
+# CHECK-LABEL: Start analyzing II
+# CHECK: MaxStallCycle is 0
+
+---
+name:            test_window_stall_cycle
+tracksRegLiveness: true
+body:             |
+  bb.0:
+    successors: %bb.3(0x40000000), %bb.1(0x40000000)
+    liveins: $r0, $r1
+  
+    %0:intregs = COPY $r1
+    %1:intregs = COPY $r0
+    %2:intregs = nsw A2_add %0, %1
+    %3:intregs = S2_lsr_i_r_acc %2, %2, 31
+    %4:intregs = S2_asr_i_r killed %3, 1
+    %5:predregs = C2_cmpgt %1, %4
+    %6:intregs = A2_tfrsi 0
+    J2_jumpt killed %5, %bb.3, implicit-def dead $pc
+    J2_jump %bb.1, implicit-def dead $pc
+  
+  bb.1:
+    successors: %bb.2(0x80000000)
+  
+    %7:intregs = A2_addi %4, 2
+    %8:intregs = A2_tfrsi 0
+    %9:intregs = A2_sub %4, %1
+    %10:intregs = A2_addi %9, 1
+    %11:intregs = COPY %10
+    J2_loop0r %bb.2, %11, implicit-def $lc0, implicit-def $sa0, implicit-def $usr
+  
+  bb.2 (machine-block-address-taken):
+    successors: %bb.3(0x04000000), %bb.2(0x7c000000)
+  
+    %12:intregs = PHI %7, %bb.1, %13, %bb.2
+    %14:intregs = PHI %8, %bb.1, %15, %bb.2
+    %16:intregs = PHI %8, %bb.1, %17, %bb.2
+    %18:intregs, %13:intregs = L2_loadri_pi %12, -4
+    %17:intregs = nsw A2_add killed %18, %16
+    %15:intregs = A2_max %17, %14
+    ENDLOOP0 %bb.2, implicit-def $pc, implicit-def $lc0, implicit $sa0, implicit $lc0
+    J2_jump %bb.3, implicit-def dead $pc
+  
+  bb.3:
+    %19:intregs = PHI %6, %bb.0, %15, %bb.2
+    $r0 = COPY %19
+    PS_jmpret $r31, implicit-def dead $pc, implicit $r0
+
+...