[Mlir-commits] [mlir] 4aeb2a5 - [MLIR][Presburger][Simplex] addSymbolicCut: don't add symbol div if denom is 1

[Arjun P]

Author: Arjun P
Date: 2022-04-12T12:27:27+01:00
New Revision: 4aeb2a57f4699de4118e0b2508918235daaf408d

URL: https://github.com/llvm/llvm-project/commit/4aeb2a57f4699de4118e0b2508918235daaf408d
DIFF: https://github.com/llvm/llvm-project/commit/4aeb2a57f4699de4118e0b2508918235daaf408d.diff

LOG: [MLIR][Presburger][Simplex] addSymbolicCut: don't add symbol div if denom is 1

This is unncessary, so we remove it as an optimization.

Reviewed By: Groverkss

Differential Revision: https://reviews.llvm.org/D123540

Added: 
    

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

Removed: 
    


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diff  --git a/mlir/lib/Analysis/Presburger/Simplex.cpp b/mlir/lib/Analysis/Presburger/Simplex.cpp
index 5e679e68b1ac7..220ea1520a464 100644
--- a/mlir/lib/Analysis/Presburger/Simplex.cpp
+++ b/mlir/lib/Analysis/Presburger/Simplex.cpp
@@ -357,8 +357,8 @@ bool SymbolicLexSimplex::isSymbolicSampleIntegral(unsigned row) const {
          isRangeDivisibleBy(tableau.getRow(row).slice(3, nSymbol), denom);
 }
 
-/// This proceeds similarly to LexSimplex::addCut(). We are given a row that has
-/// a symbolic sample value with fractional coefficients.
+/// This proceeds similarly to LexSimplexBase::addCut(). We are given a row that
+/// has a symbolic sample value with fractional coefficients.
 ///
 /// Let the row be
 /// (c + coeffM*M + sum_i a_i*s_i + sum_j b_j*y_j)/d,
@@ -374,10 +374,11 @@ bool SymbolicLexSimplex::isSymbolicSampleIntegral(unsigned row) const {
 /// sum_i (b_i%d)y_i = ((-c%d) + sum_i (-a_i%d)s_i)%d + k*d for some integer k
 ///
 /// where we take a modulo of the whole symbolic expression on the right to
-/// bring it into the range [0, d - 1]. Therefore, as in LexSimplex::addCut,
+/// bring it into the range [0, d - 1]. Therefore, as in addCut(),
 /// k is the quotient on dividing the LHS by d, and since LHS >= 0, we have
-/// k >= 0 as well. We realize the modulo of the symbolic expression by adding a
-/// division variable
+/// k >= 0 as well. If all the a_i are divisible by d, then we can add the
+/// constraint directly.  Otherwise, we realize the modulo of the symbolic
+/// expression by adding a division variable
 ///
 /// q = ((-c%d) + sum_i (-a_i%d)s_i)/d
 ///
@@ -392,16 +393,22 @@ bool SymbolicLexSimplex::isSymbolicSampleIntegral(unsigned row) const {
 LogicalResult SymbolicLexSimplex::addSymbolicCut(unsigned row) {
   int64_t d = tableau(row, 0);
 
-  // Add the division variable `q` described above to the symbol domain.
-  // q = ((-c%d) + sum_i (-a_i%d)s_i)/d.
+  // Construct the division variable `q = ((-c%d) + sum_i (-a_i%d)s_i)/d`.
   SmallVector<int64_t, 8> divCoeffs;
   divCoeffs.reserve(nSymbol + 1);
   int64_t divDenom = d;
   for (unsigned col = 3; col < 3 + nSymbol; ++col)
     divCoeffs.push_back(mod(-tableau(row, col), divDenom)); // (-a_i%d)s_i
   divCoeffs.push_back(mod(-tableau(row, 1), divDenom));     // -c%d.
-
   normalizeDiv(divCoeffs, divDenom);
+
+  if (divDenom == 1) {
+    // The symbolic sample numerator is divisible by the denominator,
+    // so the division isn't needed. We can add the constraint directly,
+    // i.e., ignore the symbols and add a regular cut as in addCut().
+    return addCut(row);
+  }
+
   domainSimplex.addDivisionVariable(divCoeffs, divDenom);
   domainPoly.addLocalFloorDiv(divCoeffs, divDenom);