[GlobalISel] Take the result size into account when const folding icmp

Author: KRM7

llvm/include/llvm/CodeGen/GlobalISel/Utils.h

@@ -325,6 +325,7 @@ ConstantFoldCountZeros(Register Src, const MachineRegisterInfo &MRI,
 
 std::optional<SmallVector<APInt>>
 ConstantFoldICmp(unsigned Pred, const Register Op1, const Register Op2,
+                 unsigned DstSizeInBits, unsigned ExtOp,
                  const MachineRegisterInfo &MRI);
 
 /// Test if the given value is known to have exactly one bit set. This differs

llvm/lib/CodeGen/GlobalISel/CSEMIRBuilder.cpp

@@ -189,10 +189,12 @@ MachineInstrBuilder CSEMIRBuilder::buildInstr(unsigned Opc,
     assert(SrcOps.size() == 3 && "Invalid sources");
     assert(DstOps.size() == 1 && "Invalid dsts");
     LLT SrcTy = SrcOps[1].getLLTTy(*getMRI());
+    LLT DstTy = DstOps[0].getLLTTy(*getMRI());
+    auto BoolExtOp = getBoolExtOp(SrcTy.isVector(), false);
 
-    if (std::optional<SmallVector<APInt>> Cst =
-            ConstantFoldICmp(SrcOps[0].getPredicate(), SrcOps[1].getReg(),
-                             SrcOps[2].getReg(), *getMRI())) {
+    if (std::optional<SmallVector<APInt>> Cst = ConstantFoldICmp(
+            SrcOps[0].getPredicate(), SrcOps[1].getReg(), SrcOps[2].getReg(),
+            DstTy.getScalarSizeInBits(), BoolExtOp, *getMRI())) {
       if (SrcTy.isVector())
         return buildBuildVectorConstant(DstOps[0], *Cst);
       return buildConstant(DstOps[0], Cst->front());

llvm/lib/CodeGen/GlobalISel/Utils.cpp

@@ -1027,39 +1027,47 @@ llvm::ConstantFoldCountZeros(Register Src, const MachineRegisterInfo &MRI,
 
 std::optional<SmallVector<APInt>>
 llvm::ConstantFoldICmp(unsigned Pred, const Register Op1, const Register Op2,
+                       unsigned DstSizeInBits, unsigned ExtOp,
                        const MachineRegisterInfo &MRI) {
+  assert(ExtOp == TargetOpcode::G_SEXT || ExtOp == TargetOpcode::G_ZEXT ||
+         ExtOp == TargetOpcode::G_ANYEXT);
+
   LLT Ty = MRI.getType(Op1);
   if (Ty != MRI.getType(Op2))
     return std::nullopt;
 
-  auto TryFoldScalar = [&MRI, Pred](Register LHS,
-                                    Register RHS) -> std::optional<APInt> {
+  const APInt FalseCst = APInt::getZero(DstSizeInBits);
+  const APInt TrueCst = (ExtOp == TargetOpcode::G_SEXT)
+                            ? APInt::getAllOnes(DstSizeInBits)
+                            : APInt::getOneBitSet(DstSizeInBits, 0);
+
+  auto TryFoldScalar = [&](Register LHS, Register RHS) -> std::optional<APInt> {
     auto LHSCst = getIConstantVRegVal(LHS, MRI);
     auto RHSCst = getIConstantVRegVal(RHS, MRI);
     if (!LHSCst || !RHSCst)
       return std::nullopt;
 
     switch (Pred) {
     case CmpInst::Predicate::ICMP_EQ:
-      return APInt(/*numBits=*/1, LHSCst->eq(*RHSCst));
+      return LHSCst->eq(*RHSCst) ? TrueCst : FalseCst;
     case CmpInst::Predicate::ICMP_NE:
-      return APInt(/*numBits=*/1, LHSCst->ne(*RHSCst));
+      return LHSCst->ne(*RHSCst) ? TrueCst : FalseCst;
     case CmpInst::Predicate::ICMP_UGT:
-      return APInt(/*numBits=*/1, LHSCst->ugt(*RHSCst));
+      return LHSCst->ugt(*RHSCst) ? TrueCst : FalseCst;
     case CmpInst::Predicate::ICMP_UGE:
-      return APInt(/*numBits=*/1, LHSCst->uge(*RHSCst));
+      return LHSCst->uge(*RHSCst) ? TrueCst : FalseCst;
     case CmpInst::Predicate::ICMP_ULT:
-      return APInt(/*numBits=*/1, LHSCst->ult(*RHSCst));
+      return LHSCst->ult(*RHSCst) ? TrueCst : FalseCst;
     case CmpInst::Predicate::ICMP_ULE:
-      return APInt(/*numBits=*/1, LHSCst->ule(*RHSCst));
+      return LHSCst->ule(*RHSCst) ? TrueCst : FalseCst;
     case CmpInst::Predicate::ICMP_SGT:
-      return APInt(/*numBits=*/1, LHSCst->sgt(*RHSCst));
+      return LHSCst->sgt(*RHSCst) ? TrueCst : FalseCst;
     case CmpInst::Predicate::ICMP_SGE:
-      return APInt(/*numBits=*/1, LHSCst->sge(*RHSCst));
+      return LHSCst->sge(*RHSCst) ? TrueCst : FalseCst;
     case CmpInst::Predicate::ICMP_SLT:
-      return APInt(/*numBits=*/1, LHSCst->slt(*RHSCst));
+      return LHSCst->slt(*RHSCst) ? TrueCst : FalseCst;
     case CmpInst::Predicate::ICMP_SLE:
-      return APInt(/*numBits=*/1, LHSCst->sle(*RHSCst));
+      return LHSCst->sle(*RHSCst) ? TrueCst : FalseCst;
     default:
       return std::nullopt;
     }

llvm/unittests/CodeGen/GlobalISel/CSETest.cpp

@@ -500,6 +500,18 @@ TEST_F(AArch64GISelMITest, TestConstantFoldICMP) {
     EXPECT_TRUE(I->getOperand(1).getCImm()->getZExtValue());
   }
 
+  {
+    auto I = CSEB.buildICmp(CmpInst::Predicate::ICMP_EQ, s32, One, One);
+    EXPECT_TRUE(I->getOpcode() == TargetOpcode::G_CONSTANT);
+    EXPECT_TRUE(I->getOperand(1).getCImm()->getZExtValue());
+  }
+
+  {
+    auto I = CSEB.buildICmp(CmpInst::Predicate::ICMP_EQ, s32, One, Two);
+    EXPECT_TRUE(I->getOpcode() == TargetOpcode::G_CONSTANT);
+    EXPECT_FALSE(I->getOperand(1).getCImm()->getZExtValue());
+  }
+
   LLT VecTy = LLT::fixed_vector(2, s32);
   LLT DstTy = LLT::fixed_vector(2, s1);
   auto Three = CSEB.buildConstant(s32, 3);