[llvm][CodeGen] Fixed max cycle calculation with zero-cost instructions for window scheduler (#99454)

We discovered some scheduling failures occurring when zero-cost
instructions were involved. This issue will be addressed by this patch.

Author: kaiyan96

llvm/lib/CodeGen/WindowScheduler.cpp

@@ -440,12 +440,16 @@ int WindowScheduler::calculateMaxCycle(ScheduleDAGInstrs &DAG,
       int PredCycle = getOriCycle(PredMI);
       ExpectCycle = std::max(ExpectCycle, PredCycle + (int)Pred.getLatency());
     }
-    // ResourceManager can be used to detect resource conflicts between the
-    // current MI and the previously inserted MIs.
-    while (!RM.canReserveResources(*SU, CurCycle) || CurCycle < ExpectCycle) {
-      ++CurCycle;
-      if (CurCycle == (int)WindowIILimit)
-        return CurCycle;
+    // Zero cost instructions do not need to check resource.
+    if (!TII->isZeroCost(MI.getOpcode())) {
+      // ResourceManager can be used to detect resource conflicts between the
+      // current MI and the previously inserted MIs.
+      while (!RM.canReserveResources(*SU, CurCycle) || CurCycle < ExpectCycle) {
+        ++CurCycle;
+        if (CurCycle == (int)WindowIILimit)
+          return CurCycle;
+      }
+      RM.reserveResources(*SU, CurCycle);
     }
     RM.reserveResources(*SU, CurCycle);
     OriToCycle[getOriMI(&MI)] = CurCycle;

llvm/test/CodeGen/Hexagon/swp-ws-zero-cost.mir

@@ -0,0 +1,45 @@
+# REQUIRES: asserts
+# RUN: llc --march=hexagon %s -run-pass=pipeliner -debug-only=pipeliner \
+# RUN: -window-sched=force -filetype=null -verify-machineinstrs 2>&1 \
+# RUN: | FileCheck %s
+
+# CHECK-NOT: Can't find a valid II. Keep searching...
+# CHECK: Start analyzing II
+# CHECK: Start scheduling Phis
+# CHECK: Current window Offset is {{[0-9]+}} and II is {{[0-9]+}}
+
+---
+name:            relu
+tracksRegLiveness: true
+body:             |
+  bb.0:
+    successors: %bb.2(0x30000000), %bb.1(0x50000000)
+    liveins: $r0, $r1, $r2
+    %0:intregs = COPY $r2
+    %1:intregs = COPY $r1
+    %2:intregs = COPY $r0
+    %3:predregs = C2_cmpeqi %2, 0
+    J2_jumpt killed %3, %bb.2, implicit-def dead $pc
+    J2_jump %bb.1, implicit-def dead $pc
+  bb.1:
+    successors: %bb.3(0x80000000)
+    %4:hvxvr = V6_vd0
+    %5:intregs = A2_addi %2, 31
+    %6:intregs = S2_lsr_i_r %5, 5
+    %7:intregs = COPY %6
+    J2_loop0r %bb.3, %7, implicit-def $lc0, implicit-def $sa0, implicit-def $usr
+    J2_jump %bb.3, implicit-def dead $pc
+  bb.2:
+    PS_jmpret $r31, implicit-def dead $pc
+  bb.3 (machine-block-address-taken):
+    successors: %bb.3(0x7c000000), %bb.2(0x04000000)
+    %8:intregs = PHI %1, %bb.1, %9, %bb.3
+    %10:intregs = PHI %0, %bb.1, %14, %bb.3
+    %11:hvxvr, %9:intregs = V6_vL32b_pi %8, 128
+    %12:intregs = COPY %10
+    %13:hvxvr = V6_vmaxw killed %11, %4
+    %14:intregs = V6_vS32b_pi %12, 128, killed %13
+    ENDLOOP0 %bb.3, implicit-def $pc, implicit-def $lc0, implicit $sa0, implicit $lc0
+    J2_jump %bb.2, implicit-def dead $pc
+...
+