[llvm] [DAG] isGuaranteedNotToBeUndefOrPoisonForTargetNode - add fallback implementation (PR #86125)

[Simon Pilgrim via llvm-commits]

https://github.com/RKSimon created https://github.com/llvm/llvm-project/pull/86125

Allow targets to rely on TargetLowering::isGuaranteedNotToBeUndefOrPoisonForTargetNode to test nodes for canCreateUndefOrPoisonForTargetNode + all arguments are isGuaranteedNotToBeUndefOrPoison.

Targets can still perform this themselves for specific special case nodes (e.g. target shuffles).

Matches the fallback in SelectionDAG::isGuaranteedNotToBeUndefOrPoison

>From d066a859ac5951981f9a260db0ad5c66da39575b Mon Sep 17 00:00:00 2001
From: Simon Pilgrim <llvm-dev at redking.me.uk>
Date: Thu, 21 Mar 2024 14:25:47 +0000
Subject: [PATCH] [DAG] isGuaranteedNotToBeUndefOrPoisonForTargetNode - add
 fallback implementation

Allow targets to rely on TargetLowering::isGuaranteedNotToBeUndefOrPoisonForTargetNode to test nodes for canCreateUndefOrPoisonForTargetNode + all arguments are isGuaranteedNotToBeUndefOrPoison.

Targets can still perform this themselves for specific nodes (e.g. target shuffles).

Matches the fallback in SelectionDAG::isGuaranteedNotToBeUndefOrPoison
---
 llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp   |  5 +++--
 llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp | 10 +++++++++-
 2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index 9d73a42df2a479..cd6f083243d09c 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -5042,8 +5042,9 @@ bool SelectionDAG::isGuaranteedNotToBeUndefOrPoison(SDValue Op,
 
   // If Op can't create undef/poison and none of its operands are undef/poison
   // then Op is never undef/poison.
-  // NOTE: TargetNodes should handle this in themselves in
-  // isGuaranteedNotToBeUndefOrPoisonForTargetNode.
+  // NOTE: TargetNodes can handle this in themselves in
+  // isGuaranteedNotToBeUndefOrPoisonForTargetNode or let
+  // TargetLowering::isGuaranteedNotToBeUndefOrPoisonForTargetNode handle it.
   return !canCreateUndefOrPoison(Op, PoisonOnly, /*ConsiderFlags*/ true,
                                  Depth) &&
          all_of(Op->ops(), [&](SDValue V) {
diff --git a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
index 57f8fc409de453..da29b1d5b312f8 100644
--- a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
@@ -3786,7 +3786,15 @@ bool TargetLowering::isGuaranteedNotToBeUndefOrPoisonForTargetNode(
        Op.getOpcode() == ISD::INTRINSIC_VOID) &&
       "Should use isGuaranteedNotToBeUndefOrPoison if you don't know whether Op"
       " is a target node!");
-  return false;
+
+  // If Op can't create undef/poison and none of its operands are undef/poison
+  // then Op is never undef/poison.
+  return !canCreateUndefOrPoisonForTargetNode(Op, DemandedElts, DAG, PoisonOnly,
+                                              /*ConsiderFlags*/ true, Depth) &&
+         all_of(Op->ops(), [&](SDValue V) {
+           return DAG.isGuaranteedNotToBeUndefOrPoison(V, PoisonOnly,
+                                                       Depth + 1);
+         });
 }
 
 bool TargetLowering::canCreateUndefOrPoisonForTargetNode(