[llvm] [InstCombine] Fold comparison of adding two z/sext booleans (PR #67895)

[Yingwei Zheng via llvm-commits]

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@@ -879,7 +879,8 @@ define i1 @zext_sext_add_icmp_slt_minus_1_no_oneuse(i1 %a, i1 %b) {
 ; CHECK-NEXT:    [[SEXT_B:%.*]] = sext i1 [[B:%.*]] to i8
 ; CHECK-NEXT:    [[ADD:%.*]] = add nsw i8 [[ZEXT_A]], [[SEXT_B]]
 ; CHECK-NEXT:    call void @use(i8 [[ADD]])
-; CHECK-NEXT:    ret i1 false
+; CHECK-NEXT:    [[R:%.*]] = icmp slt i8 [[ADD]], -1
----------------
dtcxzyw wrote:

```
static Value *createLogicFromTable(const std::bitset<4> &Table, Value *Op0,
                                   Value *Op1, IRBuilderBase &Builder, bool HasOneUse) {
  switch (Table.to_ulong()) {
  case 0: // 0 0 0 0
    return Builder.getFalse();
  case 1: // 0 0 0 1
    return HasOneUse ? Builder.CreateNot(Builder.CreateOr(Op0, Op1)) : nullptr;
  case 2: // 0 0 1 0
    return HasOneUse ? Builder.CreateAnd(Builder.CreateNot(Op0), Op1) : nullptr;
  case 3: // 0 0 1 1
    return Builder.CreateNot(Op0);
  case 4: // 0 1 0 0
    return HasOneUse ? Builder.CreateAnd(Op0, Builder.CreateNot(Op1)) : nullptr;
  case 5: // 0 1 0 1
    return Builder.CreateNot(Op1);
  case 6: // 0 1 1 0
    return Builder.CreateXor(Op0, Op1);
  case 7: // 0 1 1 1
    return HasOneUse ? Builder.CreateNot(Builder.CreateAnd(Op0, Op1)) : nullptr;
  case 8: // 1 0 0 0
    return Builder.CreateAnd(Op0, Op1);
  case 9: // 1 0 0 1
    return HasOneUse ? Builder.CreateNot(Builder.CreateXor(Op0, Op1)) : nullptr;
  case 10: // 1 0 1 0
    return Op1;
  case 11: // 1 0 1 1
    return HasOneUse ? Builder.CreateOr(Builder.CreateNot(Op0), Op1) : nullptr;
  case 12: // 1 1 0 0
    return Op0;
  case 13: // 1 1 0 1
    return HasOneUse ? Builder.CreateOr(Op0, Builder.CreateNot(Op1)) : nullptr;
  case 14: // 1 1 1 0
    return Builder.CreateOr(Op0, Op1);
  case 15: // 1 1 1 1
    return Builder.getTrue();
  default:
    llvm_unreachable("Invalid Operation");
  }
  return nullptr;
}
```
```
 if (match(Add, m_Add(
                     m_CombineAnd(m_Instruction(Ext0),
                                  m_OneUse(m_ZExtOrSExt(m_Value(Op0)))),
                     m_CombineAnd(m_Instruction(Ext1),
                                  m_OneUse(m_ZExtOrSExt(m_Value(Op1)))))) &&
```
```
  if (auto *Cond = createLogicFromTable(Table, Op0, Op1, Builder, Add->hasOneUse()))
    return replaceInstUsesWith(Cmp, Cond);
```
Then we can apply these optimizations for adds with multi-use without penalty.


https://github.com/llvm/llvm-project/pull/67895