[GlobalISel] Add isConstFalseVal helper to Utils

[paquette]

Summary

Add a utility function which returns true if the given value is a constant false value.

This is necessary to port one of the compare simplifications in TargetLowering::SimplifySetCC.

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

 bool isBuildVectorAllOnes(const MachineInstr &MI,
                           const MachineRegisterInfo &MRI);
 
 /// Returns true if given the TargetLowering's boolean contents information,
 /// the value \p Val contains a true value.
 bool isConstTrueVal(const TargetLowering &TLI, int64_t Val, bool IsVector,
                     bool IsFP);
 
+/// Returns true if given the TargetLowering's boolean contents information,
+/// the value \p Val contains a false value.
+bool isConstFalseVal(const TargetLowering &TLI, int64_t Val, bool IsVector,
+                     bool IsFP);
+
 /// \returns true if \p Val is a true value extended from \p OrigTy to \p ExtTy.
 /// \p IsFP is true if the value is floating point.
 /// \p IsSignExtended is true if the extension should be signed.
 bool isExtendedTrueVal(const TargetLowering &TLI, int64_t Val, const LLT &ExtTy,
                        const LLT &OrigTy, bool IsFP, bool IsSignExtended);
 
 /// Returns an integer representing true, as defined by the
 /// TargetBooleanContents.
 int64_t getICmpTrueVal(const TargetLowering &TLI, bool IsVector, bool IsFP);
 } // End namespace llvm.
 #endif

llvm/lib/CodeGen/GlobalISel/Utils.cpp

bool llvm::isConstTrueVal(const TargetLowering &TLI, int64_t Val, bool IsVector,
   case TargetLowering::ZeroOrOneBooleanContent:
     return Val == 1;
   case TargetLowering::ZeroOrNegativeOneBooleanContent:
     return Val == -1;
   }
   llvm_unreachable("Invalid boolean contents");
 }
 
+bool llvm::isConstFalseVal(const TargetLowering &TLI, int64_t Val,
+                           bool IsVector, bool IsFP) {
+  switch (TLI.getBooleanContents(IsVector, IsFP)) {
+  case TargetLowering::UndefinedBooleanContent:
+    return ~Val & 0x1;
+  case TargetLowering::ZeroOrOneBooleanContent:
+  case TargetLowering::ZeroOrNegativeOneBooleanContent:
+    return Val == 0;
+  }
+  llvm_unreachable("Invalid boolean contents");
+}
+
 bool llvm::isExtendedTrueVal(const TargetLowering &TLI, int64_t Val,
                              const LLT &ExtTy, const LLT &OrigTy, bool IsFP,
                              bool IsSignExtended) {
   assert(ExtTy.isVector() == OrigTy.isVector() &&
          "Expected either both scalars or both vectors?");
   assert(OrigTy.getSizeInBits() <= ExtTy.getSizeInBits() &&
          "Extended type cannot be smaller than original type?");
   auto S1 = LLT::scalar(1);

llvm/unittests/CodeGen/GlobalISel/GISelUtilsTest.cpp

for (auto IsFP : BooleanChoices) {
 
     EXPECT_FALSE(isExtendedTrueVal(TLI, 1, V2S64, V2S32, IsFP, SExt));
     EXPECT_FALSE(isExtendedTrueVal(TLI, 567, V2S64, V2S32, IsFP, SExt));
     EXPECT_FALSE(isExtendedTrueVal(TLI, -1, V2S64, V2S32, IsFP, ZExt));
     EXPECT_FALSE(isExtendedTrueVal(TLI, 1, V2S64, V2S32, IsFP, ZExt));
   }
 }
 
+TEST_F(AArch64GISelMITest, ConstFalseTest) {
+  setUp();
+  if (!TM)
+    return;
+  const auto &TLI = *B.getMF().getSubtarget().getTargetLowering();
+  bool BooleanChoices[2] = {true, false};
+
+  // AArch64 uses ZeroOrOneBooleanContent for scalars, and
+  // ZeroOrNegativeOneBooleanContent for vectors.
+  for (auto IsVec : BooleanChoices) {
+    for (auto IsFP : BooleanChoices) {
+      EXPECT_TRUE(isConstFalseVal(TLI, 0, IsVec, IsFP));
+      EXPECT_FALSE(isConstFalseVal(TLI, 1, IsVec, IsFP));
+
+      // This would be true with UndefinedBooleanContent.
+      EXPECT_FALSE(isConstFalseVal(TLI, 2, IsVec, IsFP));
+    }
+  }
+}
+
 } // namespace