[llvm] [InstCombine] Teach tryFactorization to treat a disjoint Or like an Add. (PR #75691)

[Craig Topper via llvm-commits]

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@@ -1566,14 +1566,14 @@ define i32 @mul_no_common_bits_uses(i32 %p1, i32 %p2) {
   ret i32 %r
 }
 
-; negative test - probably not good to create an extra mul
+; TODO: is it good to create an extra mul?
 
 define i32 @mul_no_common_bits_const_op_uses(i32 %p) {
 ; CHECK-LABEL: @mul_no_common_bits_const_op_uses(
 ; CHECK-NEXT:    [[X:%.*]] = and i32 [[P:%.*]], 7
 ; CHECK-NEXT:    [[M:%.*]] = mul nuw nsw i32 [[X]], 24
 ; CHECK-NEXT:    call void @use(i32 [[M]])
-; CHECK-NEXT:    [[R:%.*]] = or disjoint i32 [[M]], [[X]]
+; CHECK-NEXT:    [[R:%.*]] = mul nuw nsw i32 [[X]], 25
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topperc wrote:

I did some investigation of how to add the one use check. It's a little complicated.  The optimization can produce a Mul that can be transformed into a Shl. In that case the one use check wouldn't need to apply. The optimization can also turn a Shl into a Mul that would need the one use check to apply.

https://github.com/llvm/llvm-project/pull/75691