[llvm] [InstCombine] Fold `(X & C1) | C2` into `X & (C1 | C2)` iff `(X & C2) == C2` (PR #76470)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: Yingwei Zheng (dtcxzyw)

<details>
<summary>Changes</summary>

Alive2: https://alive2.llvm.org/ce/z/VKJYaS


---
Full diff: https://github.com/llvm/llvm-project/pull/76470.diff


2 Files Affected:

- (modified) llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp (+8) 
- (modified) llvm/test/Transforms/InstCombine/or.ll (+95) 


``````````diff
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
index 63b1e0f64a8824..6958418ba7f3fa 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -3872,6 +3872,14 @@ Instruction *InstCombinerImpl::visitOr(BinaryOperator &I) {
     }
   }
 
+  // (X & C1) | C2 -> X & (C1 | C2) iff (X & C2) == C2
+  if (match(Op0, m_OneUse(m_And(m_Value(X), m_APInt(C1)))) &&
+      match(Op1, m_APInt(C2))) {
+    KnownBits KnownX = computeKnownBits(X, /*Depth*/ 0, &I);
+    if ((KnownX.One & *C2) == *C2)
+      return BinaryOperator::CreateAnd(X, ConstantInt::get(Ty, *C1 | *C2));
+  }
+
   return nullptr;
 }
 
diff --git a/llvm/test/Transforms/InstCombine/or.ll b/llvm/test/Transforms/InstCombine/or.ll
index 805546099398b4..010ef239744188 100644
--- a/llvm/test/Transforms/InstCombine/or.ll
+++ b/llvm/test/Transforms/InstCombine/or.ll
@@ -1636,3 +1636,98 @@ define i32 @assoc_cast_assoc_disjoint(i16 %x) {
   %c = or disjoint i32 %b, 65536
   ret i32 %c
 }
+
+; (X & C1) | C2 -> X & (C1 | C2) iff (X & C2) == C2
+define i32 @test_or_and_disjoint(i32 %a) {
+; CHECK-LABEL: @test_or_and_disjoint(
+; CHECK-NEXT:    [[A0:%.*]] = and i32 [[A:%.*]], 24
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i32 [[A0]], 8
+; CHECK-NEXT:    br i1 [[CMP]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
+; CHECK:       if.then:
+; CHECK-NEXT:    [[A2:%.*]] = and i32 [[A]], 15
+; CHECK-NEXT:    ret i32 [[A2]]
+; CHECK:       if.else:
+; CHECK-NEXT:    ret i32 0
+;
+  %a0 = and i32 %a, 24
+  %cmp = icmp eq i32 %a0, 8
+  br i1 %cmp, label %if.then, label %if.else
+if.then:
+  %a1 = and i32 %a, 7
+  %a2 = or i32 %a1, 8
+  ret i32 %a2
+if.else:
+  ret i32 0
+}
+
+define i32 @test_or_and_mixed(i32 %a) {
+; CHECK-LABEL: @test_or_and_mixed(
+; CHECK-NEXT:    [[A0:%.*]] = and i32 [[A:%.*]], 27
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i32 [[A0]], 11
+; CHECK-NEXT:    br i1 [[CMP]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
+; CHECK:       if.then:
+; CHECK-NEXT:    [[A2:%.*]] = and i32 [[A]], 15
+; CHECK-NEXT:    ret i32 [[A2]]
+; CHECK:       if.else:
+; CHECK-NEXT:    ret i32 0
+;
+  %a0 = and i32 %a, 27
+  %cmp = icmp eq i32 %a0, 11
+  br i1 %cmp, label %if.then, label %if.else
+if.then:
+  %a1 = and i32 %a, 7
+  %a2 = or i32 %a1, 11
+  ret i32 %a2
+if.else:
+  ret i32 0
+}
+
+; Negative tests
+
+define i32 @test_or_and_disjoint_fail(i32 %a) {
+; CHECK-LABEL: @test_or_and_disjoint_fail(
+; CHECK-NEXT:    [[A0:%.*]] = and i32 [[A:%.*]], 24
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i32 [[A0]], 16
+; CHECK-NEXT:    br i1 [[CMP]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
+; CHECK:       if.then:
+; CHECK-NEXT:    [[A1:%.*]] = and i32 [[A]], 7
+; CHECK-NEXT:    [[A2:%.*]] = or disjoint i32 [[A1]], 8
+; CHECK-NEXT:    ret i32 [[A2]]
+; CHECK:       if.else:
+; CHECK-NEXT:    ret i32 0
+;
+  %a0 = and i32 %a, 24
+  %cmp = icmp eq i32 %a0, 16
+  br i1 %cmp, label %if.then, label %if.else
+if.then:
+  %a1 = and i32 %a, 7
+  %a2 = or i32 %a1, 8
+  ret i32 %a2
+if.else:
+  ret i32 0
+}
+
+define i32 @test_or_and_disjoint_multiuse(i32 %a) {
+; CHECK-LABEL: @test_or_and_disjoint_multiuse(
+; CHECK-NEXT:    [[A0:%.*]] = and i32 [[A:%.*]], 24
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i32 [[A0]], 8
+; CHECK-NEXT:    br i1 [[CMP]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
+; CHECK:       if.then:
+; CHECK-NEXT:    [[A1:%.*]] = and i32 [[A]], 7
+; CHECK-NEXT:    call void @use(i32 [[A1]])
+; CHECK-NEXT:    [[A2:%.*]] = or disjoint i32 [[A1]], 8
+; CHECK-NEXT:    ret i32 [[A2]]
+; CHECK:       if.else:
+; CHECK-NEXT:    ret i32 0
+;
+  %a0 = and i32 %a, 24
+  %cmp = icmp eq i32 %a0, 8
+  br i1 %cmp, label %if.then, label %if.else
+if.then:
+  %a1 = and i32 %a, 7
+  call void @use(i32 %a1)
+  %a2 = or i32 %a1, 8
+  ret i32 %a2
+if.else:
+  ret i32 0
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/76470