[llvm] [ValueTracking] Compute known bits for `umin` and `umax` recurrences (PR #222890)

[Nikita Popov via llvm-commits]

=?utf-8?q?Ömer_Sinan_Ağacan?= <omer at osa1.net>,
=?utf-8?q?Ömer_Sinan_Ağacan?= <omer at osa1.net>,
=?utf-8?q?Ömer_Sinan_Ağacan?= <omer at osa1.net>,
=?utf-8?q?Ömer_Sinan_Ağacan?= <omer at osa1.net>
Message-ID:
In-Reply-To: <llvm.org/llvm/llvm-project/pull/222890 at github.com>


================
@@ -1971,6 +1975,43 @@ static void computeKnownBitsFromOperator(const Operator *I,
       default:
         break;
       }
+    } else {
+      IntrinsicInst *II = nullptr;
+      if (matchTwoInputRecurrence<IntrinsicInst>(P, II, Start, Step)) {
+        // %iv      = [<Start>, %entry], [%iv.next, %backedge]
+        //
+        // %iv.next = <II>(%iv, <Step>)
+        // or
+        // %iv.next = <II>(<Step>, %iv)
+        Intrinsic::ID IntrinsicID = II->getIntrinsicID();
+        if (IntrinsicID == Intrinsic::umin || IntrinsicID == Intrinsic::umax) {
+          SimplifyQuery RecQ = Q.getWithoutCondContext();
+
+          unsigned OpNum = P->getOperand(0) == Start ? 0 : 1;
+          Instruction *StartInst = P->getIncomingBlock(OpNum)->getTerminator();
+          Instruction *StepInst =
+              P->getIncomingBlock(1 - OpNum)->getTerminator();
+
+          KnownBits KnownStart(BitWidth);
+          RecQ.CxtI = StartInst;
+          computeKnownBits(Start, DemandedElts, KnownStart, RecQ, Depth + 1);
+
+          KnownBits KnownStep(BitWidth);
+          RecQ.CxtI = StepInst;
+          computeKnownBits(Step, DemandedElts, KnownStep, RecQ, Depth + 1);
----------------
nikic wrote:

Might make sense to extract a common helper for this? https://github.com/osa1/llvm-project/blob/fdfb76285e8385bdaca6f802511b3e56f2b01950/llvm/lib/Analysis/ValueTracking.cpp#L1909-L1924 Or we can wait for the third copy...

https://github.com/llvm/llvm-project/pull/222890