[llvm] [InstCombine] Canonicalize xor with disjoint ops to or disjoint (PR #133139)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: Jeffrey Byrnes (jrbyrnes)

<details>
<summary>Changes</summary>

`or disjoint`s work better with other optimizations (e.g. SeparateConstOffsetFromGEP). This feels like the right place for this canonicalization, but perhaps not.

---
Full diff: https://github.com/llvm/llvm-project/pull/133139.diff


2 Files Affected:

- (modified) llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp (+5) 
- (modified) llvm/test/Transforms/InstCombine/xor.ll (+49) 


``````````diff
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
index 6cc241781d112..c8d2e5d960ec8 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -4993,6 +4993,11 @@ Instruction *InstCombinerImpl::visitXor(BinaryOperator &I) {
   if (Instruction *Abs = canonicalizeAbs(I, Builder))
     return Abs;
 
+  if (KnownBits::haveNoCommonBitsSet(
+          computeKnownBits(I.getOperand(0), /*Depth=*/0, &I),
+          computeKnownBits(I.getOperand(1), /*Depth=*/0, &I)))
+    return BinaryOperator::CreateDisjointOr(I.getOperand(0), I.getOperand(1));
+
   // Otherwise, if all else failed, try to hoist the xor-by-constant:
   //   (X ^ C) ^ Y --> (X ^ Y) ^ C
   // Just like we do in other places, we completely avoid the fold
diff --git a/llvm/test/Transforms/InstCombine/xor.ll b/llvm/test/Transforms/InstCombine/xor.ll
index 3abaf74285cc0..0cfbb2c47e21c 100644
--- a/llvm/test/Transforms/InstCombine/xor.ll
+++ b/llvm/test/Transforms/InstCombine/xor.ll
@@ -1664,3 +1664,52 @@ entry:
   %or = or <2 x i32> %add, %c
   ret <2 x i32> %or
 }
+
+declare i32 @callee()
+
+define i32 @xor_disjoint() {
+; CHECK-LABEL: @xor_disjoint(
+; CHECK-NEXT:    [[CALL1:%.*]] = call i32 @callee(), !range [[RNG0:![0-9]+]]
+; CHECK-NEXT:    [[XOR:%.*]] = or disjoint i32 [[CALL1]], 4096
+; CHECK-NEXT:    ret i32 [[XOR]]
+;
+  %call1 = call i32 @callee(), !range !0
+  %xor = xor i32 %call1, 4096
+  ret i32 %xor
+}
+
+define i32 @xor_disjoint2() {
+; CHECK-LABEL: @xor_disjoint2(
+; CHECK-NEXT:    [[CALL1:%.*]] = call i32 @callee(), !range [[RNG1:![0-9]+]]
+; CHECK-NEXT:    [[XOR:%.*]] = or disjoint i32 [[CALL1]], 512
+; CHECK-NEXT:    ret i32 [[XOR]]
+;
+  %call1 = call i32 @callee(), !range !1
+  %xor = xor i32 %call1, 512
+  ret i32 %xor
+}
+
+define i32 @xor_non_disjoint() {
+; CHECK-LABEL: @xor_non_disjoint(
+; CHECK-NEXT:    [[CALL1:%.*]] = call i32 @callee(), !range [[RNG0]]
+; CHECK-NEXT:    [[XOR:%.*]] = xor i32 [[CALL1]], 1024
+; CHECK-NEXT:    ret i32 [[XOR]]
+;
+  %call1 = call i32 @callee(), !range !0
+  %xor = xor i32 %call1, 1024
+  ret i32 %xor
+}
+
+define i32 @xor_non_disjoint2() {
+; CHECK-LABEL: @xor_non_disjoint2(
+; CHECK-NEXT:    [[CALL1:%.*]] = call i32 @callee(), !range [[RNG1]]
+; CHECK-NEXT:    [[XOR:%.*]] = and i32 [[CALL1]], 511
+; CHECK-NEXT:    ret i32 [[XOR]]
+;
+  %call1 = call i32 @callee(), !range !1
+  %xor = xor i32 %call1, 1024
+  ret i32 %xor
+}
+
+!0 = !{ i32 0, i32 2048 }
+!1 = !{ i32 1024, i32 1536 }

``````````

</details>


https://github.com/llvm/llvm-project/pull/133139