[llvm] [Analysis][NFC] Reduce memory usage of CodeMetrics (PR #198518)

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llvmorg-github-actions[bot] wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-analysis

Author: Alexis Engelke (aengelke)

<details>
<summary>Changes</summary>

FunctionSpecializer will keep the CodeMetrics of many functions at the
same time, causing the hash table in CodeMetrics to substantially
contribute to overall memory usage. Therefore, replace the DenseMap with
a vector indexed by block number.

On ArrayFunctionsRegistration.bc, this reduces the memory usage at the
time IPSCCP runs from 655.0MiB to 577.5MiB (measured with massif).


---
Full diff: https://github.com/llvm/llvm-project/pull/198518.diff


2 Files Affected:

- (modified) llvm/include/llvm/Analysis/CodeMetrics.h (+7-10) 
- (modified) llvm/lib/Analysis/CodeMetrics.cpp (+3-2) 


``````````diff
diff --git a/llvm/include/llvm/Analysis/CodeMetrics.h b/llvm/include/llvm/Analysis/CodeMetrics.h
index cf8523f540fe5..4f33e09aae199 100644
--- a/llvm/include/llvm/Analysis/CodeMetrics.h
+++ b/llvm/include/llvm/Analysis/CodeMetrics.h
@@ -14,7 +14,7 @@
 #ifndef LLVM_ANALYSIS_CODEMETRICS_H
 #define LLVM_ANALYSIS_CODEMETRICS_H
 
-#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/SmallVector.h"
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/InstructionCost.h"
 
@@ -45,23 +45,20 @@ struct CodeMetrics {
   /// one or more 'noduplicate' instructions.
   bool notDuplicatable = false;
 
-  /// The kind of convergence specified in this function.
-  ConvergenceKind Convergence = ConvergenceKind::None;
-
   /// True if this function calls alloca (in the C sense).
   bool usesDynamicAlloca = false;
 
+  /// The kind of convergence specified in this function.
+  ConvergenceKind Convergence = ConvergenceKind::None;
+
   /// Code size cost of the analyzed blocks.
   InstructionCost NumInsts = 0;
 
-  /// Number of analyzed blocks.
-  unsigned NumBlocks = false;
-
-  /// Keeps track of basic block code size estimates.
-  DenseMap<const BasicBlock *, InstructionCost> NumBBInsts;
+  /// Keeps track of basic block code size estimates. Indexed by block number.
+  SmallVector<InstructionCost, 0> NumBBInsts;
 
   /// Keep track of the number of calls to 'big' functions.
-  unsigned NumCalls = false;
+  unsigned NumCalls = 0;
 
   /// The number of calls to internal functions with a single caller.
   ///
diff --git a/llvm/lib/Analysis/CodeMetrics.cpp b/llvm/lib/Analysis/CodeMetrics.cpp
index ea67b526423bf..7c5786e16c1fb 100644
--- a/llvm/lib/Analysis/CodeMetrics.cpp
+++ b/llvm/lib/Analysis/CodeMetrics.cpp
@@ -130,7 +130,6 @@ void CodeMetrics::analyzeBasicBlock(
     const BasicBlock *BB, const TargetTransformInfo &TTI,
     const SmallPtrSetImpl<const Value *> &EphValues, bool PrepareForLTO,
     const Loop *L) {
-  ++NumBlocks;
   InstructionCost NumInstsBeforeThisBB = NumInsts;
   for (const Instruction &I : *BB) {
     // Skip ephemeral values.
@@ -231,5 +230,7 @@ void CodeMetrics::analyzeBasicBlock(
 
   // Remember NumInsts for this BB.
   InstructionCost NumInstsThisBB = NumInsts - NumInstsBeforeThisBB;
-  NumBBInsts[BB] = NumInstsThisBB;
+  if (NumBBInsts.size() <= BB->getNumber())
+    NumBBInsts.resize(BB->getParent()->getMaxBlockNumber());
+  NumBBInsts[BB->getNumber()] = NumInstsThisBB;
 }

``````````

</details>


https://github.com/llvm/llvm-project/pull/198518