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

[Philip Reames via llvm-commits]

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

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.

>From b500a487f18015498402a825402a46e87880d6d4 Mon Sep 17 00:00:00 2001
From: Philip Reames <preames at rivosinc.com>
Date: Tue, 23 Apr 2024 14:19:38 -0700
Subject: [PATCH] [DAG] Early exit for flags in canCreateUndefOrPoison [nfc]

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.
---
 llvm/include/llvm/CodeGen/SelectionDAGNodes.h |  7 +++++
 .../lib/CodeGen/SelectionDAG/SelectionDAG.cpp | 28 ++++++-------------
 2 files changed, 16 insertions(+), 19 deletions(-)

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.