[llvm] 8e75536 - [DebugInfo][InstrRef][NFC] Bypass a frequently-noop loop

[Jeremy Morse via llvm-commits]

Author: Jeremy Morse
Date: 2022-02-01T19:39:09Z
New Revision: 8e75536e510460bedcfdafb38d58cdfb7bb66111

URL: https://github.com/llvm/llvm-project/commit/8e75536e510460bedcfdafb38d58cdfb7bb66111
DIFF: https://github.com/llvm/llvm-project/commit/8e75536e510460bedcfdafb38d58cdfb7bb66111.diff

LOG: [DebugInfo][InstrRef][NFC] Bypass a frequently-noop loop

Bypass this loop if it would do nothing -- if there are no register masks
to be examined, there's no point looking at each location to see if the
location has been def'd. Awkwardly, this was responsible for almost an
entire half a percent of performance improvement on CTMark.

Differential Revision: https://reviews.llvm.org/D118613

Added: 
    

Modified: 
    llvm/lib/CodeGen/LiveDebugValues/InstrRefBasedImpl.cpp

Removed: 
    


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diff  --git a/llvm/lib/CodeGen/LiveDebugValues/InstrRefBasedImpl.cpp b/llvm/lib/CodeGen/LiveDebugValues/InstrRefBasedImpl.cpp
index c7b63111a947..2e69a5e437e7 100644
--- a/llvm/lib/CodeGen/LiveDebugValues/InstrRefBasedImpl.cpp
+++ b/llvm/lib/CodeGen/LiveDebugValues/InstrRefBasedImpl.cpp
@@ -1409,18 +1409,20 @@ void InstrRefBasedLDV::transferRegisterDef(MachineInstr &MI) {
 
   // Look for any clobbers performed by a register mask. Only test locations
   // that are actually being tracked.
-  for (auto L : MTracker->locations()) {
-    // Stack locations can't be clobbered by regmasks.
-    if (MTracker->isSpill(L.Idx))
-      continue;
+  if (!RegMaskPtrs.empty()) {
+    for (auto L : MTracker->locations()) {
+      // Stack locations can't be clobbered by regmasks.
+      if (MTracker->isSpill(L.Idx))
+        continue;
 
-    Register Reg = MTracker->LocIdxToLocID[L.Idx];
-    if (IgnoreSPAlias(Reg))
-      continue;
+      Register Reg = MTracker->LocIdxToLocID[L.Idx];
+      if (IgnoreSPAlias(Reg))
+        continue;
 
-    for (auto *MO : RegMaskPtrs)
-      if (MO->clobbersPhysReg(Reg))
-        TTracker->clobberMloc(L.Idx, MI.getIterator(), false);
+      for (auto *MO : RegMaskPtrs)
+        if (MO->clobbersPhysReg(Reg))
+          TTracker->clobberMloc(L.Idx, MI.getIterator(), false);
+    }
   }
 
   // Tell TTracker about any folded stack store.