[ConstantRanges] Use APInt for constant case for urem/srem.

Currently UREM & SREM on constant ranges produces overly pessimistic
results for single element constant ranges.

Delegate to APInt's implementation if both operands are single element
constant ranges. We already do something similar for other binary
operators, like binary AND.

Fixes PR49731.

Reviewed By: lebedev.ri

Differential Revision: https://reviews.llvm.org/D105115

1 files changed, 18 insertions, 0 deletions

diff --git a/llvm/lib/IR/ConstantRange.cpp b/llvm/lib/IR/ConstantRange.cpp
index b38599f..0649776 100644
--- a/llvm/lib/IR/ConstantRange.cpp
+++ b/llvm/lib/IR/ConstantRange.cpp
@@ -1221,6 +1221,15 @@ ConstantRange ConstantRange::urem(const ConstantRange &RHS) const {
   if (isEmptySet() || RHS.isEmptySet() || RHS.getUnsignedMax().isNullValue())
     return getEmpty();
 
+  if (const APInt *RHSInt = RHS.getSingleElement()) {
+    // UREM by null is UB.
+    if (RHSInt->isNullValue())
+      return getEmpty();
+    // Use APInt's implementation of UREM for single element ranges.
+    if (const APInt *LHSInt = getSingleElement())
+      return {LHSInt->urem(*RHSInt)};
+  }
+
   // L % R for L < R is L.
   if (getUnsignedMax().ult(RHS.getUnsignedMin()))
     return *this;
@@ -1234,6 +1243,15 @@ ConstantRange ConstantRange::srem(const ConstantRange &RHS) const {
   if (isEmptySet() || RHS.isEmptySet())
     return getEmpty();
 
+  if (const APInt *RHSInt = RHS.getSingleElement()) {
+    // SREM by null is UB.
+    if (RHSInt->isNullValue())
+      return getEmpty();
+    // Use APInt's implementation of SREM for single element ranges.
+    if (const APInt *LHSInt = getSingleElement())
+      return {LHSInt->srem(*RHSInt)};
+  }
+
   ConstantRange AbsRHS = RHS.abs();
   APInt MinAbsRHS = AbsRHS.getUnsignedMin();
   APInt MaxAbsRHS = AbsRHS.getUnsignedMax();