[llvm] DAG: Fix asserting in error case for powi softening (PR #147237)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm created https://github.com/llvm/llvm-project/pull/147237

We need to return the expected legalized type, not the original
in this case. Also swap to returning poison, and avoid contraction
in error message.

>From 5ac09bc186b80a9e56917a8b02d7f4d3b43cb9ca Mon Sep 17 00:00:00 2001
From: Matt Arsenault <Matthew.Arsenault at amd.com>
Date: Mon, 7 Jul 2025 14:12:34 +0900
Subject: [PATCH] DAG: Fix asserting in error case for powi softening

We need to return the expected legalized type, not the original
in this case. Also swap to returning poison, and avoid contraction
in error message.
---
 llvm/lib/CodeGen/SelectionDAG/LegalizeFloatTypes.cpp | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/llvm/lib/CodeGen/SelectionDAG/LegalizeFloatTypes.cpp b/llvm/lib/CodeGen/SelectionDAG/LegalizeFloatTypes.cpp
index 7dfb43164be37..64d9c1586796f 100644
--- a/llvm/lib/CodeGen/SelectionDAG/LegalizeFloatTypes.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/LegalizeFloatTypes.cpp
@@ -724,11 +724,13 @@ SDValue DAGTypeLegalizer::SoftenFloatRes_ExpOp(SDNode *N) {
   RTLIB::Libcall LC = IsPowI ? RTLIB::getPOWI(N->getValueType(0))
                              : RTLIB::getLDEXP(N->getValueType(0));
   assert(LC != RTLIB::UNKNOWN_LIBCALL && "Unexpected fpowi.");
+  EVT NVT = TLI.getTypeToTransformTo(*DAG.getContext(), N->getValueType(0));
+
   if (!TLI.getLibcallName(LC)) {
     // Some targets don't have a powi libcall; use pow instead.
     // FIXME: Implement this if some target needs it.
-    DAG.getContext()->emitError("Don't know how to soften fpowi to fpow");
-    return DAG.getUNDEF(N->getValueType(0));
+    DAG.getContext()->emitError("do not know how to soften fpowi to fpow");
+    return DAG.getPOISON(NVT);
   }
 
   if (DAG.getLibInfo().getIntSize() !=
@@ -736,10 +738,9 @@ SDValue DAGTypeLegalizer::SoftenFloatRes_ExpOp(SDNode *N) {
     // If the exponent does not match with sizeof(int) a libcall to RTLIB::POWI
     // would use the wrong type for the argument.
     DAG.getContext()->emitError("POWI exponent does not match sizeof(int)");
-    return DAG.getUNDEF(N->getValueType(0));
+    return DAG.getPOISON(NVT);
   }
 
-  EVT NVT = TLI.getTypeToTransformTo(*DAG.getContext(), N->getValueType(0));
   SDValue Ops[2] = { GetSoftenedFloat(N->getOperand(0 + Offset)),
                      N->getOperand(1 + Offset) };
   SDValue Chain = IsStrict ? N->getOperand(0) : SDValue();