[llvm] [InstCombine] Remove AllOnes fallbacks in getMaskedTypeForICmpPair() (PR #104941)

[Nikita Popov via llvm-commits]

================
@@ -252,54 +247,42 @@ static std::optional<std::pair<unsigned, unsigned>> getMaskedTypeForICmpPair(
     R1 = nullptr;
     Ok = true;
   } else {
-    if (!match(R1, m_And(m_Value(R11), m_Value(R12)))) {
-      // As before, model no mask as a trivial mask if it'll let us do an
-      // optimization.
-      R11 = R1;
-      R12 = Constant::getAllOnesValue(R1->getType());
+    if (match(R1, m_And(m_Value(R11), m_Value(R12)))) {
+      if (R11 == L11 || R11 == L12 || R11 == L21 || R11 == L22) {
+        A = R11;
+        D = R12;
+        E = R2;
+        Ok = true;
+      } else if (R12 == L11 || R12 == L12 || R12 == L21 || R12 == L22) {
+        A = R12;
+        D = R11;
+        E = R2;
+        Ok = true;
+      }
     }
 
-    if (R11 == L11 || R11 == L12 || R11 == L21 || R11 == L22) {
-      A = R11;
-      D = R12;
-      E = R2;
-      Ok = true;
-    } else if (R12 == L11 || R12 == L12 || R12 == L21 || R12 == L22) {
-      A = R12;
-      D = R11;
-      E = R2;
-      Ok = true;
+    if (match(R2, m_And(m_Value(R11), m_Value(R12)))) {
+      if (R11 == L11 || R11 == L12 || R11 == L21 || R11 == L22) {
+        A = R11;
+        D = R12;
+        E = R1;
+        Ok = true;
+      } else if (R12 == L11 || R12 == L12 || R12 == L21 || R12 == L22) {
+        A = R12;
+        D = R11;
+        E = R1;
+        Ok = true;
+      }
     }
+
+    if (!Ok)
+      return std::nullopt;
   }
 
   // Bail if RHS was a icmp that can't be decomposed into an equality.
   if (!ICmpInst::isEquality(PredR))
     return std::nullopt;
 
-  // Look for ANDs on the right side of the RHS icmp.
-  if (!Ok) {
-    if (!match(R2, m_And(m_Value(R11), m_Value(R12)))) {
-      R11 = R2;
-      R12 = Constant::getAllOnesValue(R2->getType());
-    }
-
-    if (R11 == L11 || R11 == L12 || R11 == L21 || R11 == L22) {
-      A = R11;
-      D = R12;
-      E = R1;
-      Ok = true;
-    } else if (R12 == L11 || R12 == L12 || R12 == L21 || R12 == L22) {
-      A = R12;
-      D = R11;
-      E = R1;
-      Ok = true;
-    } else {
-      return std::nullopt;
-    }
-
-    assert(Ok && "Failed to find AND on the right side of the RHS icmp.");
-  }
-
----------------
nikic wrote:

I went with this approach.

Annoyingly, @dtcxzyw's case does actually need to match on -1 here. I ended up handling that case separately via https://github.com/llvm/llvm-project/commit/32679e10a9b66405c340213993f65b2edf5a794a.

https://github.com/llvm/llvm-project/pull/104941