[llvm] Fujun.han/instcombine or to xor (PR #75129)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: Fujun Han (Peter9606)

<details>
<summary>Changes</summary>

Simplify a complex OR to XOR

    Following pattern:
      (or (and x, half_c1), c3), (and x, c2))
      IFF
        c1, c2, c3 is constant
        c1 is pow2
        c2 < c1
        c3 == (c1 - 1) ^ c2
        half_c1 = (lshr c1, 1)
        (c1 >> 1) & c3 == (c1 >> 1)
        x is known to be less than c1
    can be simplified into:
      (xor x, half_c)

Proof: https://alive2.llvm.org/ce/z/Lfax3w


---
Full diff: https://github.com/llvm/llvm-project/pull/75129.diff


2 Files Affected:

- (modified) llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp (+21-1) 
- (added) llvm/test/Transforms/InstCombine/or-and-add-constant-constant-and-constant.ll (+36) 


``````````diff
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
index 6002f599ca71ab..67ec4a1608169a 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -3343,6 +3343,27 @@ Instruction *InstCombinerImpl::visitOr(BinaryOperator &I) {
   if (Instruction *X = foldComplexAndOrPatterns(I, Builder))
     return X;
 
+  // Change (or (and (add x, half_c1), c3), (and x, c2)) to (xor x, half_c1),
+  // iff c1, c2, c3 is constant, and half_c1 = (lshr c1, 1),  and c1 is pow2,
+  // and c2 < c1, and c3 == (c1 - 1) ^ c2, and (c1 >> 1) & c3 == (c1 >> 1) and x
+  // is known to be less than c1.
+  Type *Ty = I.getType();
+  if (Ty->isIntegerTy()) {
+    Value *X = nullptr;
+    const APInt *HalfC1 = nullptr, *C2 = nullptr, *C3 = nullptr;
+    if (match(&I,
+              m_c_Or(m_c_And(m_c_Add(m_Value(X), m_APInt(HalfC1)), m_APInt(C3)),
+                     m_c_And(m_Value(X), m_APInt(C2))))) {
+      const APInt C1 = HalfC1->shl(1);
+      KnownBits KnownX = computeKnownBits(X, 0, nullptr);
+      if (C1.isPowerOf2() && C2->ult(C1) && (*C3 == (*C2 ^ (C1 - 1))) &&
+          ((*HalfC1 & *C3) == *HalfC1) && KnownX.getMaxValue().ult(C1)) {
+        Value *Xor = Builder.CreateXor(X, ConstantInt::get(Ty, *HalfC1));
+        return replaceInstUsesWith(I, Xor);
+      }
+    }
+  }
+
   // (A&B)|(A&C) -> A&(B|C) etc
   if (Value *V = foldUsingDistributiveLaws(I))
     return replaceInstUsesWith(I, V);
@@ -3351,7 +3372,6 @@ Instruction *InstCombinerImpl::visitOr(BinaryOperator &I) {
     return replaceInstUsesWith(I, V);
 
   Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
-  Type *Ty = I.getType();
   if (Ty->isIntOrIntVectorTy(1)) {
     if (auto *SI0 = dyn_cast<SelectInst>(Op0)) {
       if (auto *R =
diff --git a/llvm/test/Transforms/InstCombine/or-and-add-constant-constant-and-constant.ll b/llvm/test/Transforms/InstCombine/or-and-add-constant-constant-and-constant.ll
new file mode 100644
index 00000000000000..3e48f3c3f331b9
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/or-and-add-constant-constant-and-constant.ll
@@ -0,0 +1,36 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -passes=instcombine -S | FileCheck %s
+
+; Pattern:
+;   (or (and (add x, half_c1), c3), (and x, c2))
+; IFF:
+;   c1, c2, c3 is constant
+;   c1 is pow2
+;   c2 < c1
+;   c3 == (c1 - 1) ^ c2
+;   half_c1 == (lshr c1, 1)
+;   (c1 >> 1) & c3 == (c1 >> 1)
+;   x is known to be less than c1
+; Could be transformed into:
+;   (xor x, half_c1)
+; Proof: https://alive2.llvm.org/ce/z/Lfax3w
+
+define i16 @or_and_add_and() {
+; CHECK-LABEL: @or_and_add_and(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[X:%.*]] = call i16 @dummy(), !range [[RNG0:![0-9]+]]
+; CHECK-NEXT:    [[OR:%.*]] = xor i16 [[X]], 32
+; CHECK-NEXT:    ret i16 [[OR]]
+;
+entry:
+  %x = call i16 @dummy(), !range !0
+  %add = add i16 32, %x
+  %and1 = and i16 %add, 48
+  %and2 = and i16 %x, 15
+  %or = or i16 %and1, %and2
+  ret i16 %or
+}
+
+declare i16 @dummy()
+
+!0 = !{i16 0, i16 64}

``````````

</details>


https://github.com/llvm/llvm-project/pull/75129