[Mlir-commits] [mlir] 31ddc7e - [mlir][presburger] Avoid redundant zero-initialization in insertColumns (#199911)

[llvmlistbot at llvm.org]

Author: lonely eagle
Date: 2026-07-11T23:58:06+08:00
New Revision: 31ddc7e564814a42af39f0e71371469d0b1fca24

URL: https://github.com/llvm/llvm-project/commit/31ddc7e564814a42af39f0e71371469d0b1fca24
DIFF: https://github.com/llvm/llvm-project/commit/31ddc7e564814a42af39f0e71371469d0b1fca24.diff

LOG: [mlir][presburger] Avoid redundant zero-initialization in insertColumns (#199911)

When insertColumns does not trigger a physical reallocation, the inner
loop needlessly loops up to nReservedColumns - 1. This causes massive
redundant zero-writes on trailing columns that are already zero. This
patch truncates the inner loop start boundary to nColumns - 1, when the
reserved capacity is unchanged, optimizing the non-realloc path from
O(nRows * nReservedColumns) to O(nRows * nColumns).

Added: 
    

Modified: 
    mlir/lib/Analysis/Presburger/Matrix.cpp

Removed: 
    


################################################################################
diff  --git a/mlir/lib/Analysis/Presburger/Matrix.cpp b/mlir/lib/Analysis/Presburger/Matrix.cpp
index 89d8a15422d95..7c55caa767c45 100644
--- a/mlir/lib/Analysis/Presburger/Matrix.cpp
+++ b/mlir/lib/Analysis/Presburger/Matrix.cpp
@@ -160,17 +160,17 @@ void Matrix<T>::insertColumns(unsigned pos, unsigned count) {
   }
   nColumns += count;
 
+  int colStart = nColumns - 1;
+  if (oldNReservedColumns != nReservedColumns)
+    colStart = nReservedColumns - 1;
   for (int ri = nRows - 1; ri >= 0; --ri) {
-    for (int ci = nReservedColumns - 1; ci >= 0; --ci) {
+    for (int ci = colStart; ci >= 0; --ci) {
       unsigned r = ri;
       unsigned c = ci;
       T &dest = data[r * nReservedColumns + c];
       if (c >= nColumns) { // NOLINT
         // Out of bounds columns are zero-initialized. NOLINT because clang-tidy
         // complains about this branch being the same as the c >= pos one.
-        //
-        // TODO: this case can be skipped if the number of reserved columns
-        // didn't change.
         dest = 0;
       } else if (c >= pos + count) {
         // Shift the data occuring after the inserted columns.