[NFC][InstCombine] '(Op1 & С) - Op1' -> '-(Op1 & ~C)' fold (PR44427)

This decreases use count of Op1, potentially allows
us to further hoist said 'neg' later on,
and results in marginally better X86 codegen.

Name: (Op1 & С) - Op1 -> -(Op1 & ~C)
  %o = and i64 %Op1, C1
  %r = sub i64 %o, %Op1
=>
  %n = and i64 %Op1, ~C1
  %r = sub i64 0, %n

https://rise4fun.com/Alive/rwgA

https://godbolt.org/z/R_RMfM

https://bugs.llvm.org/show_bug.cgi?id=44427

1 files changed, 9 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index 33803aaf359..9676c6abef0 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -1889,6 +1889,15 @@ Instruction *InstCombiner::visitSub(BinaryOperator &I) {
     }
   }
 
+  {
+    // (sub (and Op1, C), Op1) --> neg (and Op1, ~C)
+    Constant *C;
+    if (match(Op0, m_OneUse(m_And(m_Specific(Op1), m_Constant(C))))) {
+      return BinaryOperator::CreateNeg(
+          Builder.CreateAnd(Op1, Builder.CreateNot(C)));
+    }
+  }
+
   if (Op1->hasOneUse()) {
     Value *X = nullptr, *Y = nullptr, *Z = nullptr;
     Constant *C = nullptr;