Fix sign of largest known divisor of div.

[jreiffers]

There's a missing abs, so it returns a negative value if the divisor is negative. Later this is then cast to uint.

[llvmbot]

@llvm/pr-subscribers-mlir-core

Author: Johannes Reifferscheid (jreiffers)

Changes

There's a missing abs, so it returns a negative value if the divisor is negative. Later this is then cast to uint.

---

Full diff: https://github.com/llvm/llvm-project/pull/100081.diff

2 Files Affected:

• (modified) mlir/lib/IR/AffineExpr.cpp (+2-1)
• (modified) mlir/unittests/IR/AffineExprTest.cpp (+6)

diff --git a/mlir/lib/IR/AffineExpr.cpp b/mlir/lib/IR/AffineExpr.cpp
index 75cc01ee9a146..7978b35e7147d 100644
--- a/mlir/lib/IR/AffineExpr.cpp
+++ b/mlir/lib/IR/AffineExpr.cpp
@@ -6,6 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include <cmath>
 #include <cstdint>
 #include <limits>
 #include <utility>
@@ -257,7 +258,7 @@ int64_t AffineExpr::getLargestKnownDivisor() const {
     if (rhs && rhs.getValue() != 0) {
       int64_t lhsDiv = binExpr.getLHS().getLargestKnownDivisor();
       if (lhsDiv % rhs.getValue() == 0)
-        return lhsDiv / rhs.getValue();
+        return std::abs(lhsDiv / rhs.getValue());
     }
     return 1;
   }
diff --git a/mlir/unittests/IR/AffineExprTest.cpp b/mlir/unittests/IR/AffineExprTest.cpp
index 75c893334943d..dc78bbac85f3c 100644
--- a/mlir/unittests/IR/AffineExprTest.cpp
+++ b/mlir/unittests/IR/AffineExprTest.cpp
@@ -106,3 +106,9 @@ TEST(AffineExprTest, modSimplificationRegression) {
   auto sum = d0 + d0.floorDiv(3).floorDiv(-3);
   ASSERT_EQ(sum.getKind(), AffineExprKind::Add);
 }
+
+TEST(AffineExprTest, divisorOfNegativeFloorDiv) {
+  MLIRContext ctx;
+  OpBuilder b(&ctx);
+  ASSERT_EQ(b.getAffineDimExpr(0).floorDiv(-1).getLargestKnownDivisor(), 1);
+}

[llvmbot]

@llvm/pr-subscribers-mlir

Author: Johannes Reifferscheid (jreiffers)

Changes

There's a missing abs, so it returns a negative value if the divisor is negative. Later this is then cast to uint.

---

Full diff: https://github.com/llvm/llvm-project/pull/100081.diff

2 Files Affected:

• (modified) mlir/lib/IR/AffineExpr.cpp (+2-1)
• (modified) mlir/unittests/IR/AffineExprTest.cpp (+6)

diff --git a/mlir/lib/IR/AffineExpr.cpp b/mlir/lib/IR/AffineExpr.cpp
index 75cc01ee9a146..7978b35e7147d 100644
--- a/mlir/lib/IR/AffineExpr.cpp
+++ b/mlir/lib/IR/AffineExpr.cpp
@@ -6,6 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include <cmath>
 #include <cstdint>
 #include <limits>
 #include <utility>
@@ -257,7 +258,7 @@ int64_t AffineExpr::getLargestKnownDivisor() const {
     if (rhs && rhs.getValue() != 0) {
       int64_t lhsDiv = binExpr.getLHS().getLargestKnownDivisor();
       if (lhsDiv % rhs.getValue() == 0)
-        return lhsDiv / rhs.getValue();
+        return std::abs(lhsDiv / rhs.getValue());
     }
     return 1;
   }
diff --git a/mlir/unittests/IR/AffineExprTest.cpp b/mlir/unittests/IR/AffineExprTest.cpp
index 75c893334943d..dc78bbac85f3c 100644
--- a/mlir/unittests/IR/AffineExprTest.cpp
+++ b/mlir/unittests/IR/AffineExprTest.cpp
@@ -106,3 +106,9 @@ TEST(AffineExprTest, modSimplificationRegression) {
   auto sum = d0 + d0.floorDiv(3).floorDiv(-3);
   ASSERT_EQ(sum.getKind(), AffineExprKind::Add);
 }
+
+TEST(AffineExprTest, divisorOfNegativeFloorDiv) {
+  MLIRContext ctx;
+  OpBuilder b(&ctx);
+  ASSERT_EQ(b.getAffineDimExpr(0).floorDiv(-1).getLargestKnownDivisor(), 1);
+}