[llvm] 91fb66c - [DebugInfo][InstrRef][NFC] Don't build a map of un-needed values

[Jeremy Morse via llvm-commits]

Author: Jeremy Morse
Date: 2022-02-01T18:58:06Z
New Revision: 91fb66cf91ae557d45bde7931cbb364f1c08d245

URL: https://github.com/llvm/llvm-project/commit/91fb66cf91ae557d45bde7931cbb364f1c08d245
DIFF: https://github.com/llvm/llvm-project/commit/91fb66cf91ae557d45bde7931cbb364f1c08d245.diff

LOG: [DebugInfo][InstrRef][NFC] Don't build a map of un-needed values

When finding locations for variable values at the start of a block, we
build a large map of every value to every location, and then pick out the
locations for values that are desired. This takes up quite a lot of time,
because, unsurprisingly, there are usually more values in registers and
stack slots than there are variables.

This patch instead creates a map of desired values to their locations,
which are initially illegal locations. Then, as we examine every available
value, we can select locations for values we care about, and ignore those
that we don't. This substantially reduces the amount of work done (i.e.,
building a map up of values to locations that nothing wants or needs).

Geomean performance improvement of 1% on CTMark, woo.

Differential Revision: https://reviews.llvm.org/D118597

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 90cd448eefc4f..61d127d7a2943 100644
--- a/llvm/lib/CodeGen/LiveDebugValues/InstrRefBasedImpl.cpp
+++ b/llvm/lib/CodeGen/LiveDebugValues/InstrRefBasedImpl.cpp
@@ -274,6 +274,13 @@ class TransferTracker {
 
     // Map of the preferred location for each value.
     DenseMap<ValueIDNum, LocIdx> ValueToLoc;
+
+    // Initialized the preferred-location map with illegal locations, to be
+    // filled in later.
+    for (auto &VLoc : VLocs)
+      if (VLoc.second.Kind == DbgValue::Def)
+        ValueToLoc.insert({VLoc.second.ID, LocIdx::MakeIllegalLoc()});
+
     ActiveMLocs.reserve(VLocs.size());
     ActiveVLocs.reserve(VLocs.size());
 
@@ -285,21 +292,20 @@ class TransferTracker {
       ValueIDNum &VNum = MLocs[Idx.asU64()];
       VarLocs.push_back(VNum);
 
-      // Short-circuit unnecessary preferred location update.
-      if (VLocs.empty())
+      // Is there a variable that wants a location for this value? If not, skip.
+      auto VIt = ValueToLoc.find(VNum);
+      if (VIt == ValueToLoc.end())
         continue;
 
-      auto it = ValueToLoc.find(VNum);
+      LocIdx CurLoc = VIt->second;
       // In order of preference, pick:
       //  * Callee saved registers,
       //  * Other registers,
       //  * Spill slots.
-      if (it == ValueToLoc.end() || MTracker->isSpill(it->second) ||
-          (!isCalleeSaved(it->second) && isCalleeSaved(Idx.asU64()))) {
+      if (CurLoc.isIllegal() || MTracker->isSpill(CurLoc) ||
+          (!isCalleeSaved(CurLoc) && isCalleeSaved(Idx.asU64()))) {
         // Insert, or overwrite if insertion failed.
-        auto PrefLocRes = ValueToLoc.insert(std::make_pair(VNum, Idx));
-        if (!PrefLocRes.second)
-          PrefLocRes.first->second = Idx;
+        VIt->second = Idx;
       }
     }
 
@@ -314,7 +320,7 @@ class TransferTracker {
       // If the value has no location, we can't make a variable location.
       const ValueIDNum &Num = Var.second.ID;
       auto ValuesPreferredLoc = ValueToLoc.find(Num);
-      if (ValuesPreferredLoc == ValueToLoc.end()) {
+      if (ValuesPreferredLoc->second.isIllegal()) {
         // If it's a def that occurs in this block, register it as a
         // use-before-def to be resolved as we step through the block.
         if (Num.getBlock() == (unsigned)MBB.getNumber() && !Num.isPHI())