[llvm][CodeGen] Added missing initialization failure information for window scheduler (#99449)

Summary: Added missing initialization failure information for window scheduler.

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Differential Revision: https://phabricator.intern.facebook.com/D60250707

Author: kaiyan96

llvm/lib/CodeGen/WindowScheduler.cpp

@@ -232,8 +232,11 @@ bool WindowScheduler::initialize() {
       return false;
     }
     for (auto &Def : MI.all_defs())
-      if (Def.isReg() && Def.getReg().isPhysical())
+      if (Def.isReg() && Def.getReg().isPhysical()) {
+        LLVM_DEBUG(dbgs() << "Physical registers are not supported in "
+                             "window scheduling!\n");
         return false;
+      }
   }
   if (SchedInstrNum <= WindowRegionLimit) {
     LLVM_DEBUG(dbgs() << "There are too few MIs in the window region!\n");

llvm/test/CodeGen/Hexagon/swp-ws-fail-2.mir

@@ -3,6 +3,7 @@
 # RUN: -window-sched=force -filetype=null -verify-machineinstrs 2>&1 \
 # RUN: | FileCheck %s
 
+# CHECK: Physical registers are not supported in window scheduling!
 # CHECK: The WindowScheduler failed to initialize!
 
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