use SmallDenseMap in DelinearizationCache for better compile time

Author: sebpop

llvm/include/llvm/Analysis/DependenceAnalysis.h

@@ -402,11 +402,13 @@ class DependenceInfo {
   /// leading to better precision (similar to Polly's approach).
   struct DelinearizationCache {
     /// Map from base pointer to computed array dimension sizes.
-    DenseMap<const SCEVUnknown *, SmallVector<const SCEV *, 4>> ArraySizes;
+    SmallDenseMap<const SCEVUnknown *, SmallVector<const SCEV *, 4>, 8>
+        ArraySizes;
     /// Map from instruction to pre-computed subscripts.
-    DenseMap<const Instruction *, SmallVector<const SCEV *, 4>> Subscripts;
+    SmallDenseMap<const Instruction *, SmallVector<const SCEV *, 4>, 16>
+        Subscripts;
     /// Element size for the array (used for validation).
-    DenseMap<const SCEVUnknown *, const SCEV *> ElementSizes;
+    SmallDenseMap<const SCEVUnknown *, const SCEV *, 8> ElementSizes;
     /// Flag indicating whether the cache has been populated.
     bool IsPopulated = false;
   };

llvm/lib/Analysis/DependenceAnalysis.cpp

@@ -3783,8 +3783,8 @@ void DependenceInfo::populateDelinearizationCache() {
 
   // Step 1: Collect all memory accesses grouped by base pointer.
   // Map from base pointer to list of (Instruction, AccessFunction) pairs.
-  DenseMap<const SCEVUnknown *,
-           SmallVector<std::pair<Instruction *, const SCEV *>, 4>>
+  SmallDenseMap<const SCEVUnknown *,
+                SmallVector<std::pair<Instruction *, const SCEV *>, 4>, 8>
       AccessesByBase;
 
   for (Instruction &I : instructions(*F)) {