[llvm] [SelectionDAG] Detect impossible conditions using known bits analysis (PR #150715)

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github-actions[bot] wrote:

<!--LLVM CODE FORMAT COMMENT: {clang-format}-->


:warning: C/C++ code formatter, clang-format found issues in your code. :warning:

<details>
<summary>
You can test this locally with the following command:
</summary>

``````````bash
git-clang-format --diff HEAD~1 HEAD --extensions cpp -- llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
``````````

</details>

<details>
<summary>
View the diff from clang-format here.
</summary>

``````````diff
diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 9dbfcb146..08f4f4656 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -13534,48 +13534,68 @@ SDValue DAGCombiner::visitSETCC(SDNode *N) {
     ConstantSDNode *N1C = cast<ConstantSDNode>(N1);
     APInt C1 = N1C->getAPIntValue();
     KnownBits KnownRHS = KnownBits::makeConstant(C1);
-    
+
     // Bail out early if RHS is unknown (shouldn't happen for constants)
     if (KnownRHS.isUnknown())
       return SDValue();
-    
+
     std::optional<bool> KnownVal;
-    
+
     // Handle special cases first (like GlobalISel does)
     if (KnownRHS.isZero()) {
       // x >=u 0 -> always true
-      // x <u 0 -> always false  
+      // x <u 0 -> always false
       if (Cond == ISD::SETUGE)
         KnownVal = true;
       else if (Cond == ISD::SETULT)
         KnownVal = false;
     }
-    
+
     // If not handled by special cases, use ICmpInst::compare
     if (!KnownVal) {
       KnownBits KnownLHS = DAG.computeKnownBits(N0);
-      
+
       // Convert ISD::CondCode to CmpInst::Predicate
       CmpInst::Predicate Pred;
       switch (Cond) {
-      case ISD::SETEQ:  Pred = CmpInst::ICMP_EQ; break;
-      case ISD::SETNE:  Pred = CmpInst::ICMP_NE; break;
-      case ISD::SETULT: Pred = CmpInst::ICMP_ULT; break;
-      case ISD::SETULE: Pred = CmpInst::ICMP_ULE; break;
-      case ISD::SETUGT: Pred = CmpInst::ICMP_UGT; break;
-      case ISD::SETUGE: Pred = CmpInst::ICMP_UGE; break;
-      case ISD::SETLT:  Pred = CmpInst::ICMP_SLT; break;
-      case ISD::SETLE:  Pred = CmpInst::ICMP_SLE; break;
-      case ISD::SETGT:  Pred = CmpInst::ICMP_SGT; break;
-      case ISD::SETGE:  Pred = CmpInst::ICMP_SGE; break;
-      default: 
+      case ISD::SETEQ:
+        Pred = CmpInst::ICMP_EQ;
+        break;
+      case ISD::SETNE:
+        Pred = CmpInst::ICMP_NE;
+        break;
+      case ISD::SETULT:
+        Pred = CmpInst::ICMP_ULT;
+        break;
+      case ISD::SETULE:
+        Pred = CmpInst::ICMP_ULE;
+        break;
+      case ISD::SETUGT:
+        Pred = CmpInst::ICMP_UGT;
+        break;
+      case ISD::SETUGE:
+        Pred = CmpInst::ICMP_UGE;
+        break;
+      case ISD::SETLT:
+        Pred = CmpInst::ICMP_SLT;
+        break;
+      case ISD::SETLE:
+        Pred = CmpInst::ICMP_SLE;
+        break;
+      case ISD::SETGT:
+        Pred = CmpInst::ICMP_SGT;
+        break;
+      case ISD::SETGE:
+        Pred = CmpInst::ICMP_SGE;
+        break;
+      default:
         return SDValue(); // Unsupported predicate
       }
-      
+
       // Use the same logic as GlobalISel: ICmpInst::compare
       KnownVal = ICmpInst::compare(KnownLHS, KnownRHS, Pred);
     }
-    
+
     // If the comparison result is known, replace with constant
     if (KnownVal)
       return DAG.getConstant(*KnownVal ? 1 : 0, DL, VT);

``````````

</details>


https://github.com/llvm/llvm-project/pull/150715