[PATCH] D63505: [InstCombine] Fold icmp eq/ne (and %x, ~C), 0 -> %x u</u>= 0 earlier, C+1 is power of 2.

[Huihui Zhang via Phabricator via llvm-commits]

huihuiz marked an inline comment as done.
huihuiz added inline comments.


================
Comment at: llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp:1643-1645
   // Don't perform the following transforms if the AND has multiple uses
   if (!And->hasOneUse())
     return nullptr;
----------------
lebedev.ri wrote:
> Why are we restricting this fold to single-use `and`?
Same reason in D63026 (resolving PR10267)


================
Comment at: llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp:1656-1657
+    // ((X & ~7) == 0) --> X u< 8
+    // If X is (BinOp Y, C3), allow other rules to fold C3 with C2.
+    if (!match(X, m_c_BinOp(m_Value(), m_Constant())) &&
+        (~(*C2) + 1).isPowerOf2()) {
----------------
lebedev.ri wrote:
> Why do we care about that? Seems rather arbitrary.
take this test as example


```
define i1 @test_shift_and_cmp_changed2(i8 %p) {
  %shlp = shl i8 %p, 5
  %andp = and i8 %shlp, -64
  %cmp = icmp ult i8 %andp, 32
  ret i1 %cmp
}

```

we do miss fold for (X >> C3) & C2 != C1 --> (X & (C2 << C3)) != (C1 << C3)


Repository:
  rL LLVM

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  https://reviews.llvm.org/D63505/new/

https://reviews.llvm.org/D63505