Reapply [IR] Avoid creating icmp/fcmp constant expressions (#92885)

Reapply after https://github.com/llvm/llvm-project/pull/93548,
which should address the lldb failure on macos.

-----

Do not create icmp/fcmp constant expressions in IRBuilder etc anymore,
i.e. treat them as "undesirable". This is in preparation for removing
them entirely.

Part of:
https://discourse.llvm.org/t/rfc-remove-most-constant-expressions/63179

1 files changed, 8 insertions, 5 deletions

diff --git a/llvm/lib/IR/ConstantFold.cpp b/llvm/lib/IR/ConstantFold.cpp
index 9a7d437..0ef92ea 100644
--- a/llvm/lib/IR/ConstantFold.cpp
+++ b/llvm/lib/IR/ConstantFold.cpp
@@ -1282,9 +1282,9 @@ Constant *llvm::ConstantFoldCompareInstruction(CmpInst::Predicate Predicate,
     // Fast path for splatted constants.
     if (Constant *C1Splat = C1->getSplatValue())
       if (Constant *C2Splat = C2->getSplatValue())
-        return ConstantVector::getSplat(
-            C1VTy->getElementCount(),
-            ConstantExpr::getCompare(Predicate, C1Splat, C2Splat));
+        if (Constant *Elt =
+                ConstantFoldCompareInstruction(Predicate, C1Splat, C2Splat))
+          return ConstantVector::getSplat(C1VTy->getElementCount(), Elt);
 
     // Do not iterate on scalable vector. The number of elements is unknown at
     // compile-time.
@@ -1302,8 +1302,11 @@ Constant *llvm::ConstantFoldCompareInstruction(CmpInst::Predicate Predicate,
           ConstantExpr::getExtractElement(C1, ConstantInt::get(Ty, I));
       Constant *C2E =
           ConstantExpr::getExtractElement(C2, ConstantInt::get(Ty, I));
+      Constant *Elt = ConstantFoldCompareInstruction(Predicate, C1E, C2E);
+      if (!Elt)
+        return nullptr;
 
-      ResElts.push_back(ConstantExpr::getCompare(Predicate, C1E, C2E));
+      ResElts.push_back(Elt);
     }
 
     return ConstantVector::get(ResElts);
@@ -1411,7 +1414,7 @@ Constant *llvm::ConstantFoldCompareInstruction(CmpInst::Predicate Predicate,
       // other way if possible.
       // Also, if C1 is null and C2 isn't, flip them around.
       Predicate = ICmpInst::getSwappedPredicate(Predicate);
-      return ConstantExpr::getICmp(Predicate, C2, C1);
+      return ConstantFoldCompareInstruction(Predicate, C2, C1);
     }
   }
   return nullptr;