[llvm] [DAG] Early exit for flags in canCreateUndefOrPoison [nfc] (PR #89834)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-selectiondag

Author: Philip Reames (preames)

<details>
<summary>Changes</summary>

This matches the style used in the Analysis version of this routine, and makes it less likely we'll miss a poison generating flag in future changes.  Unlike IR, the check for poison generating flags is near trivial since all nodes have the SDFlags storage, and all bits in that storage is poison generating.

---
Full diff: https://github.com/llvm/llvm-project/pull/89834.diff


2 Files Affected:

- (modified) llvm/include/llvm/CodeGen/SelectionDAGNodes.h (+7) 
- (modified) llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp (+9-19) 


``````````diff
diff --git a/llvm/include/llvm/CodeGen/SelectionDAGNodes.h b/llvm/include/llvm/CodeGen/SelectionDAGNodes.h
index 261f7e49e5c8ca..bf73015ed888ed 100644
--- a/llvm/include/llvm/CodeGen/SelectionDAGNodes.h
+++ b/llvm/include/llvm/CodeGen/SelectionDAGNodes.h
@@ -452,6 +452,13 @@ struct SDNodeFlags {
   bool hasNoFPExcept() const { return NoFPExcept; }
   bool hasUnpredictable() const { return Unpredictable; }
 
+  bool hasAny() const {
+    return NoUnsignedWrap || NoSignedWrap || Exact || Disjoint || NonNeg ||
+           NoNaNs || NoInfs || NoSignedZeros || AllowReciprocal ||
+           AllowContract || ApproximateFuncs || AllowReassociation ||
+           NoFPExcept || Unpredictable;
+  }
+
   /// Clear any flags in this flag set that aren't also set in Flags. All
   /// flags will be cleared if Flags are undefined.
   void intersectWith(const SDNodeFlags Flags) {
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index b63b8b893fdbf1..de0c5c0305ad57 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -5095,6 +5095,10 @@ bool SelectionDAG::canCreateUndefOrPoison(SDValue Op, const APInt &DemandedElts,
   if (VT.isScalableVector())
     return true;
 
+  // Matches hasPoisonGeneratingFlags().
+  if (ConsiderFlags && Op->getFlags().hasAny())
+    return true;
+
   unsigned Opcode = Op.getOpcode();
   switch (Opcode) {
   case ISD::FREEZE:
@@ -5134,34 +5138,20 @@ bool SelectionDAG::canCreateUndefOrPoison(SDValue Op, const APInt &DemandedElts,
       return true;
 
     const TargetOptions &Options = getTarget().Options;
-    return Options.NoNaNsFPMath || Options.NoInfsFPMath ||
-           (ConsiderFlags &&
-            (Op->getFlags().hasNoNaNs() || Op->getFlags().hasNoInfs()));
+    return Options.NoNaNsFPMath || Options.NoInfsFPMath;
   }
 
-  // Matches hasPoisonGeneratingFlags().
+  case ISD::OR:
   case ISD::ZERO_EXTEND:
-    return ConsiderFlags && Op->getFlags().hasNonNeg();
-
   case ISD::ADD:
   case ISD::SUB:
   case ISD::MUL:
-    // Matches hasPoisonGeneratingFlags().
-    return ConsiderFlags && (Op->getFlags().hasNoSignedWrap() ||
-                             Op->getFlags().hasNoUnsignedWrap());
+    // No poison except from flags (which is handled above)
+    return false;
 
   case ISD::SHL:
     // If the max shift amount isn't in range, then the shift can create poison.
-    if (!getValidMaximumShiftAmountConstant(Op, DemandedElts))
-      return true;
-
-    // Matches hasPoisonGeneratingFlags().
-    return ConsiderFlags && (Op->getFlags().hasNoSignedWrap() ||
-                             Op->getFlags().hasNoUnsignedWrap());
-
-  // Matches hasPoisonGeneratingFlags().
-  case ISD::OR:
-    return ConsiderFlags && Op->getFlags().hasDisjoint();
+    return !getValidMaximumShiftAmountConstant(Op, DemandedElts);
 
   case ISD::SCALAR_TO_VECTOR:
     // Check if we demand any upper (undef) elements.

``````````

</details>


https://github.com/llvm/llvm-project/pull/89834