[ConstExpr] Don't create div/rem expressions

This removes creation of udiv/sdiv/urem/srem constant expressions,
in preparation for their removal. I've added a
ConstantExpr::isDesirableBinOp() predicate to determine whether
an expression should be created for a certain operator.

With this patch, div/rem expressions can still be created through
explicit IR/bitcode, forbidding them entirely will be the next step.

Differential Revision: https://reviews.llvm.org/D128820

1 files changed, 21 insertions, 6 deletions

diff --git a/llvm/lib/IR/ConstantFold.cpp b/llvm/lib/IR/ConstantFold.cpp
index 41b4f29..98adff1 100644
--- a/llvm/lib/IR/ConstantFold.cpp
+++ b/llvm/lib/IR/ConstantFold.cpp
@@ -1218,9 +1218,13 @@ Constant *llvm::ConstantFoldBinaryInstruction(unsigned Opcode, Constant *C1,
       if (Instruction::isIntDivRem(Opcode) && C2Splat->isNullValue())
         return PoisonValue::get(VTy);
       if (Constant *C1Splat = C1->getSplatValue()) {
-        return ConstantVector::getSplat(
-            VTy->getElementCount(),
-            ConstantExpr::get(Opcode, C1Splat, C2Splat));
+        Constant *Res =
+            ConstantExpr::isDesirableBinOp(Opcode)
+                ? ConstantExpr::get(Opcode, C1Splat, C2Splat)
+                : ConstantFoldBinaryInstruction(Opcode, C1Splat, C2Splat);
+        if (!Res)
+          return nullptr;
+        return ConstantVector::getSplat(VTy->getElementCount(), Res);
       }
     }
 
@@ -1237,7 +1241,12 @@ Constant *llvm::ConstantFoldBinaryInstruction(unsigned Opcode, Constant *C1,
         if (Instruction::isIntDivRem(Opcode) && RHS->isNullValue())
           return PoisonValue::get(VTy);
 
-        Result.push_back(ConstantExpr::get(Opcode, LHS, RHS));
+        Constant *Res = ConstantExpr::isDesirableBinOp(Opcode)
+                            ? ConstantExpr::get(Opcode, LHS, RHS)
+                            : ConstantFoldBinaryInstruction(Opcode, LHS, RHS);
+        if (!Res)
+          return nullptr;
+        Result.push_back(Res);
       }
 
       return ConstantVector::get(Result);
@@ -2218,9 +2227,15 @@ Constant *llvm::ConstantFoldGetElementPtr(Type *PointeeTy, Constant *C,
               : cast<FixedVectorType>(CurrIdx->getType())->getNumElements(),
           Factor);
 
-    NewIdxs[i] = ConstantExpr::getSRem(CurrIdx, Factor);
+    NewIdxs[i] =
+        ConstantFoldBinaryInstruction(Instruction::SRem, CurrIdx, Factor);
+
+    Constant *Div =
+        ConstantFoldBinaryInstruction(Instruction::SDiv, CurrIdx, Factor);
 
-    Constant *Div = ConstantExpr::getSDiv(CurrIdx, Factor);
+    // We're working on either ConstantInt or vectors of ConstantInt,
+    // so these should always fold.
+    assert(NewIdxs[i] != nullptr && Div != nullptr && "Should have folded");
 
     unsigned CommonExtendedWidth =
         std::max(PrevIdx->getType()->getScalarSizeInBits(),