[llvm] [DAG] canCreateUndefOrPoison - poison generating flags / out of range shift amounts only generate poison (PR #196489)

[Simon Pilgrim via llvm-commits]

https://github.com/RKSimon created https://github.com/llvm/llvm-project/pull/196489

Matches ValueTracking / GISel implementations - although testing options are limited until DAG has actual uses of UndefPoisonKind::UndefOnly

>From 85558588bcbe6cc919791f41053dd6aa61a3da53 Mon Sep 17 00:00:00 2001
From: Simon Pilgrim <llvm-dev at redking.me.uk>
Date: Fri, 8 May 2026 09:52:20 +0100
Subject: [PATCH] [DAG] canCreateUndefOrPoison - poison generating flags / out
 of range shift amounts only generate poison

Matches ValueTracking / GISel implementations - although testing options are limited until DAG has actual uses of UndefPoisonKind::UndefOnly
---
 llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index a50db7c007890..b1baa007b00cb 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -5843,7 +5843,7 @@ bool SelectionDAG::canCreateUndefOrPoison(SDValue Op, const APInt &DemandedElts,
                                           UndefPoisonKind Kind,
                                           bool ConsiderFlags,
                                           unsigned Depth) const {
-  if (ConsiderFlags && Op->hasPoisonGeneratingFlags())
+  if (ConsiderFlags && includesPoison(Kind) && Op->hasPoisonGeneratingFlags())
     return true;
 
   unsigned Opcode = Op.getOpcode();
@@ -5970,7 +5970,8 @@ bool SelectionDAG::canCreateUndefOrPoison(SDValue Op, const APInt &DemandedElts,
   case ISD::SRA:
     // If the max shift amount isn't in range, then the shift can
     // create poison.
-    return !getValidMaximumShiftAmount(Op, DemandedElts, Depth + 1);
+    return includesPoison(Kind) &&
+           !getValidMaximumShiftAmount(Op, DemandedElts, Depth + 1);
 
   case ISD::CTTZ_ZERO_UNDEF:
   case ISD::CTLZ_ZERO_UNDEF: