[clang] [InstCombine] Add combines/simplifications for `llvm.ptrmask` (PR #67166)

[Nikita Popov via cfe-commits]

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@@ -6397,6 +6397,48 @@ static Value *simplifyBinaryIntrinsic(Function *F, Value *Op0, Value *Op1,
       return Constant::getNullValue(ReturnType);
     break;
   }
+  case Intrinsic::ptrmask: {
+    // Fail loudly in case this is ever changed.
+    // TODO: If vector types are supported the logic that checks if the mask is
+    // useless should be updated to use generic constants.
+    assert(!Op0->getType()->isVectorTy() && !Op1->getType()->isVectorTy() &&
+           "These simplifications where written at a time when ptrmask did not "
+           "support vector types and may not work for vectors");
+
+    // NOTE: We can't apply these simplifications based on the value of Op1
+    // because we need to preserve provenance.
+    if (isa<PoisonValue>(Op0) || isa<PoisonValue>(Op1))
+      return PoisonValue::get(Op0->getType());
+
+    if (Q.isUndefValue(Op0))
+      return Constant::getNullValue(Op0->getType());
+
+    if (match(Op0, m_Zero()))
+      return Constant::getNullValue(Op0->getType());
+
+    if (Op1->getType()->getScalarSizeInBits() ==
+        Q.DL.getPointerTypeSizeInBits(Op0->getType())) {
----------------
nikic wrote:

Drop this check now? For the following transforms:

 * The ptrtoint one is safe, but you won't actually be able to trigger it if index type is smaller.
 * The allones/undef ones are safe and can be tested.
 * The knownbits one is safe with a truncate of the known bits. Can be tested.

https://github.com/llvm/llvm-project/pull/67166