[IR] Remove support for icmp and fcmp constant expressions (#93038)

Remove support for the icmp and fcmp constant expressions.

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

As usual, many of the updated tests will no longer test what they were
originally intended to -- this is hard to preserve when constant
expressions get removed, and in many cases just impossible as the
existence of a specific kind of constant expression was the cause of the
issue in the first place.

Author: nikic

lld/test/COFF/lto-weak-undefined.ll

@@ -19,7 +19,8 @@ target triple = "x86_64-pc-windows-msvc"
 
 define dso_local i32 @main() {
 entry:
-  br i1 icmp ne (ptr @optionalFunc, ptr null), label %if.then, label %if.end
+  %cmp = icmp ne ptr @optionalFunc, null
+  br i1 %cmp, label %if.then, label %if.end
 
 if.then:
   tail call void @optionalFunc()

llvm/bindings/ocaml/llvm/llvm.ml

@@ -651,10 +651,6 @@ external const_mul : llvalue -> llvalue -> llvalue = "llvm_const_mul"
 external const_nsw_mul : llvalue -> llvalue -> llvalue = "llvm_const_nsw_mul"
 external const_nuw_mul : llvalue -> llvalue -> llvalue = "llvm_const_nuw_mul"
 external const_xor : llvalue -> llvalue -> llvalue = "llvm_const_xor"
-external const_icmp : Icmp.t -> llvalue -> llvalue -> llvalue
-                    = "llvm_const_icmp"
-external const_fcmp : Fcmp.t -> llvalue -> llvalue -> llvalue
-                    = "llvm_const_fcmp"
 external const_shl : llvalue -> llvalue -> llvalue = "llvm_const_shl"
 external const_gep : lltype -> llvalue -> llvalue array -> llvalue
                    = "llvm_const_gep"

llvm/bindings/ocaml/llvm/llvm.mli

@@ -1136,16 +1136,6 @@ val const_nuw_mul : llvalue -> llvalue -> llvalue
     See the method [llvm::ConstantExpr::getXor]. *)
 val const_xor : llvalue -> llvalue -> llvalue
 
-(** [const_icmp pred c1 c2] returns the constant comparison of two integer
-    constants, [c1 pred c2].
-    See the method [llvm::ConstantExpr::getICmp]. *)
-val const_icmp : Icmp.t -> llvalue -> llvalue -> llvalue
-
-(** [const_fcmp pred c1 c2] returns the constant comparison of two floating
-    point constants, [c1 pred c2].
-    See the method [llvm::ConstantExpr::getFCmp]. *)
-val const_fcmp : Fcmp.t -> llvalue -> llvalue -> llvalue
-
 (** [const_shl c1 c2] returns the constant integer [c1] left-shifted by the
     constant integer [c2].
     See the method [llvm::ConstantExpr::getShl]. *)

llvm/bindings/ocaml/llvm/llvm_ocaml.c

@@ -1224,18 +1224,6 @@ value llvm_const_xor(value LHS, value RHS) {
   return to_val(Value);
 }
 
-/* Icmp.t -> llvalue -> llvalue -> llvalue */
-value llvm_const_icmp(value Pred, value LHSConstant, value RHSConstant) {
-  return to_val(LLVMConstICmp(Int_val(Pred) + LLVMIntEQ, Value_val(LHSConstant),
-                              Value_val(RHSConstant)));
-}
-
-/* Fcmp.t -> llvalue -> llvalue -> llvalue */
-value llvm_const_fcmp(value Pred, value LHSConstant, value RHSConstant) {
-  return to_val(LLVMConstFCmp(Int_val(Pred), Value_val(LHSConstant),
-                              Value_val(RHSConstant)));
-}
-
 /* llvalue -> llvalue -> llvalue */
 value llvm_const_shl(value LHS, value RHS) {
   LLVMValueRef Value = LLVMConstShl(Value_val(LHS), Value_val(RHS));

llvm/docs/LangRef.rst

@@ -4821,10 +4821,6 @@ The following is the syntax for constant expressions:
     required to make sense for the type of "pointer to TY". These indexes
     may be implicitly sign-extended or truncated to match the index size
     of CSTPTR's address space.
-``icmp COND (VAL1, VAL2)``
-    Perform the :ref:`icmp operation <i_icmp>` on constants.
-``fcmp COND (VAL1, VAL2)``
-    Perform the :ref:`fcmp operation <i_fcmp>` on constants.
 ``extractelement (VAL, IDX)``
     Perform the :ref:`extractelement operation <i_extractelement>` on
     constants.

llvm/docs/ReleaseNotes.rst

@@ -56,6 +56,11 @@ Changes to the LLVM IR
 * Renamed ``llvm.experimental.vector.splice`` intrinsic to ``llvm.vector.splice``.
 * Renamed ``llvm.experimental.vector.interleave2`` intrinsic to ``llvm.vector.interleave2``.
 * Renamed ``llvm.experimental.vector.deinterleave2`` intrinsic to ``llvm.vector.deinterleave2``.
+* The constant expression variants of the following instructions have been
+  removed:
+
+  * ``icmp``
+  * ``fcmp``
 
 Changes to LLVM infrastructure
 ------------------------------
@@ -191,6 +196,14 @@ Changes to the C API
   * ``LLVMGetCallBrNumIndirectDests``
   * ``LLVMGetCallBrIndirectDest``
 
+* The following functions for creating constant expressions have been removed,
+  because the underlying constant expressions are no longer supported. Instead,
+  an instruction should be created using the ``LLVMBuildXYZ`` APIs, which will
+  constant fold the operands if possible and create an instruction otherwise:
+
+  * ``LLVMConstICmp``
+  * ``LLVMConstFCmp``
+
 Changes to the CodeGen infrastructure
 -------------------------------------
 

llvm/include/llvm-c/Core.h

@@ -2354,10 +2354,6 @@ LLVMValueRef LLVMConstMul(LLVMValueRef LHSConstant, LLVMValueRef RHSConstant);
 LLVMValueRef LLVMConstNSWMul(LLVMValueRef LHSConstant, LLVMValueRef RHSConstant);
 LLVMValueRef LLVMConstNUWMul(LLVMValueRef LHSConstant, LLVMValueRef RHSConstant);
 LLVMValueRef LLVMConstXor(LLVMValueRef LHSConstant, LLVMValueRef RHSConstant);
-LLVMValueRef LLVMConstICmp(LLVMIntPredicate Predicate,
-                           LLVMValueRef LHSConstant, LLVMValueRef RHSConstant);
-LLVMValueRef LLVMConstFCmp(LLVMRealPredicate Predicate,
-                           LLVMValueRef LHSConstant, LLVMValueRef RHSConstant);
 LLVMValueRef LLVMConstShl(LLVMValueRef LHSConstant, LLVMValueRef RHSConstant);
 LLVMValueRef LLVMConstGEP2(LLVMTypeRef Ty, LLVMValueRef ConstantVal,
                            LLVMValueRef *ConstantIndices, unsigned NumIndices);
@@ -3529,8 +3525,7 @@ LLVMOpcode LLVMGetInstructionOpcode(LLVMValueRef Inst);
 /**
  * Obtain the predicate of an instruction.
  *
- * This is only valid for instructions that correspond to llvm::ICmpInst
- * or llvm::ConstantExpr whose opcode is llvm::Instruction::ICmp.
+ * This is only valid for instructions that correspond to llvm::ICmpInst.
  *
  * @see llvm::ICmpInst::getPredicate()
  */
@@ -3539,8 +3534,7 @@ LLVMIntPredicate LLVMGetICmpPredicate(LLVMValueRef Inst);
 /**
  * Obtain the float predicate of an instruction.
  *
- * This is only valid for instructions that correspond to llvm::FCmpInst
- * or llvm::ConstantExpr whose opcode is llvm::Instruction::FCmp.
+ * This is only valid for instructions that correspond to llvm::FCmpInst.
  *
  * @see llvm::FCmpInst::getPredicate()
  */

llvm/include/llvm/IR/Constants.h

@@ -1234,30 +1234,13 @@ class ConstantExpr : public Constant {
   /// Return true if this is a convert constant expression
   bool isCast() const;
 
-  /// Return true if this is a compare constant expression
-  bool isCompare() const;
-
   /// get - Return a binary or shift operator constant expression,
   /// folding if possible.
   ///
   /// \param OnlyIfReducedTy see \a getWithOperands() docs.
   static Constant *get(unsigned Opcode, Constant *C1, Constant *C2,
                        unsigned Flags = 0, Type *OnlyIfReducedTy = nullptr);
 
-  /// Return an ICmp or FCmp comparison operator constant expression.
-  ///
-  /// \param OnlyIfReduced see \a getWithOperands() docs.
-  static Constant *getCompare(unsigned short pred, Constant *C1, Constant *C2,
-                              bool OnlyIfReduced = false);
-
-  /// get* - Return some common constants without having to
-  /// specify the full Instruction::OPCODE identifier.
-  ///
-  static Constant *getICmp(unsigned short pred, Constant *LHS, Constant *RHS,
-                           bool OnlyIfReduced = false);
-  static Constant *getFCmp(unsigned short pred, Constant *LHS, Constant *RHS,
-                           bool OnlyIfReduced = false);
-
   /// Getelementptr form.  Value* is only accepted for convenience;
   /// all elements must be Constants.
   ///
@@ -1318,10 +1301,6 @@ class ConstantExpr : public Constant {
   /// Return the opcode at the root of this constant expression
   unsigned getOpcode() const { return getSubclassDataFromValue(); }
 
-  /// Return the ICMP or FCMP predicate value. Assert if this is not an ICMP or
-  /// FCMP constant expression.
-  unsigned getPredicate() const;
-
   /// Assert that this is a shufflevector and return the mask. See class
   /// ShuffleVectorInst for a description of the mask representation.
   ArrayRef<int> getShuffleMask() const;

llvm/lib/Analysis/ConstantFolding.cpp

@@ -1009,12 +1009,8 @@ Constant *ConstantFoldInstOperandsImpl(const Value *InstOrCE, unsigned Opcode,
                                           GEP->getInRange());
   }
 
-  if (auto *CE = dyn_cast<ConstantExpr>(InstOrCE)) {
-    if (CE->isCompare())
-      return ConstantFoldCompareInstOperands(CE->getPredicate(), Ops[0], Ops[1],
-                                             DL, TLI);
+  if (auto *CE = dyn_cast<ConstantExpr>(InstOrCE))
     return CE->getWithOperands(Ops);
-  }
 
   switch (Opcode) {
   default: return nullptr;

llvm/lib/AsmParser/LLParser.cpp

@@ -4176,37 +4176,9 @@ bool LLParser::parseValID(ValID &ID, PerFunctionState *PFS, Type *ExpectedTy) {
   case lltok::kw_fptosi:
     return error(ID.Loc, "fptosi constexprs are no longer supported");
   case lltok::kw_icmp:
-  case lltok::kw_fcmp: {
-    unsigned PredVal, Opc = Lex.getUIntVal();
-    Constant *Val0, *Val1;
-    Lex.Lex();
-    if (parseCmpPredicate(PredVal, Opc) ||
-        parseToken(lltok::lparen, "expected '(' in compare constantexpr") ||
-        parseGlobalTypeAndValue(Val0) ||
-        parseToken(lltok::comma, "expected comma in compare constantexpr") ||
-        parseGlobalTypeAndValue(Val1) ||
-        parseToken(lltok::rparen, "expected ')' in compare constantexpr"))
-      return true;
-
-    if (Val0->getType() != Val1->getType())
-      return error(ID.Loc, "compare operands must have the same type");
-
-    CmpInst::Predicate Pred = (CmpInst::Predicate)PredVal;
-
-    if (Opc == Instruction::FCmp) {
-      if (!Val0->getType()->isFPOrFPVectorTy())
-        return error(ID.Loc, "fcmp requires floating point operands");
-      ID.ConstantVal = ConstantExpr::getFCmp(Pred, Val0, Val1);
-    } else {
-      assert(Opc == Instruction::ICmp && "Unexpected opcode for CmpInst!");
-      if (!Val0->getType()->isIntOrIntVectorTy() &&
-          !Val0->getType()->isPtrOrPtrVectorTy())
-        return error(ID.Loc, "icmp requires pointer or integer operands");
-      ID.ConstantVal = ConstantExpr::getICmp(Pred, Val0, Val1);
-    }
-    ID.Kind = ValID::t_Constant;
-    return false;
-  }
+    return error(ID.Loc, "icmp constexprs are no longer supported");
+  case lltok::kw_fcmp:
+    return error(ID.Loc, "fcmp constexprs are no longer supported");
 
   // Binary Operators.
   case lltok::kw_add: