[Mlir-commits] [mlir] Fix bug in `visitDivExpr` and `visitModExpr` (PR #145290)

[Arnab Dutta]

https://github.com/arnab-polymage created https://github.com/llvm/llvm-project/pull/145290

Whenever the result of a div or mod affine expression is a constant expression, place the value in the constant index of the flattened expression instead of adding it as a local expression.

>From f51da541d076a8bfc61133a2389b75c63a1a51ed Mon Sep 17 00:00:00 2001
From: Arnab Dutta <arnab at polymagelabs.com>
Date: Mon, 23 Jun 2025 14:05:32 +0530
Subject: [PATCH] Fix bug in `visitDivExpr` and `visitModExpr`

Whenever the result of a div or mod affine expression is a
constant expression, place the value in the constant index of the
flattened expression instead of adding it as a local expression.
---
 mlir/lib/IR/AffineExpr.cpp | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/mlir/lib/IR/AffineExpr.cpp b/mlir/lib/IR/AffineExpr.cpp
index cc81f9d19aca7..feedef46c66b8 100644
--- a/mlir/lib/IR/AffineExpr.cpp
+++ b/mlir/lib/IR/AffineExpr.cpp
@@ -1177,10 +1177,10 @@ static AffineExpr getSemiAffineExprFromFlatForm(ArrayRef<int64_t> flatExprs,
     if (flatExprs[numDims + numSymbols + it.index()] == 0)
       continue;
     AffineExpr expr = it.value();
-    auto binaryExpr = dyn_cast<AffineBinaryOpExpr>(expr);
-    if (!binaryExpr)
-      continue;
-
+    assert(isa<AffineBinaryOpExpr>(expr) &&
+           "local expression cannot be a dimension, symbol or a constant -- it "
+           "should be a binary op expression");
+    auto binaryExpr = cast<AffineBinaryOpExpr>(expr);
     AffineExpr lhs = binaryExpr.getLHS();
     AffineExpr rhs = binaryExpr.getRHS();
     if (!((isa<AffineDimExpr>(lhs) || isa<AffineSymbolExpr>(lhs)) &&
@@ -1348,6 +1348,11 @@ LogicalResult SimpleAffineExprFlattener::visitModExpr(AffineBinaryOpExpr expr) {
     AffineExpr divisorExpr = getAffineExprFromFlatForm(rhs, numDims, numSymbols,
                                                        localExprs, context);
     AffineExpr modExpr = dividendExpr % divisorExpr;
+    if (auto constModExpr = dyn_cast<AffineConstantExpr>(modExpr)) {
+      std::fill(lhs.begin(), lhs.end(), 0);
+      lhs[getConstantIndex()] = constModExpr.getValue();
+      return success();
+    }
     return addLocalVariableSemiAffine(modLhs, rhs, modExpr, lhs, lhs.size());
   }
 
@@ -1482,6 +1487,11 @@ LogicalResult SimpleAffineExprFlattener::visitDivExpr(AffineBinaryOpExpr expr,
     AffineExpr b = getAffineExprFromFlatForm(rhs, numDims, numSymbols,
                                              localExprs, context);
     AffineExpr divExpr = isCeil ? a.ceilDiv(b) : a.floorDiv(b);
+    if (auto constDivExpr = dyn_cast<AffineConstantExpr>(divExpr)) {
+      std::fill(lhs.begin(), lhs.end(), 0);
+      lhs[getConstantIndex()] = constDivExpr.getValue();
+      return success();
+    }
     return addLocalVariableSemiAffine(divLhs, rhs, divExpr, lhs, lhs.size());
   }