[llvm] [RISCV][TTI] Add checks for invalid cast operations (PR #88854)

[Shih-Po Hung via llvm-commits]

https://github.com/arcbbb created https://github.com/llvm/llvm-project/pull/88854

In issue #88802, the LV cost model would query the cost of the TRUNC for source type 2xi1 and destination type 2xi32. This patch adds an early exit check to prevent invalid operations.

>From a5278c4275b0eaf2d8b2b331eca18a095d2eb628 Mon Sep 17 00:00:00 2001
From: ShihPo Hung <shihpo.hung at sifive.com>
Date: Tue, 16 Apr 2024 00:59:45 -0700
Subject: [PATCH] [RISCV][TTI] Add checks for invalid cast operations

In issue #88802, the LV cost model would query the cost of
the TRUNC for source type 2xi1 and destination type 2xi32.
This patch adds an early exit check to prevent invalid operations.
---
 llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp b/llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp
index 38304ff90252f0..c4f1c275f63b65 100644
--- a/llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp
+++ b/llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp
@@ -956,6 +956,9 @@ InstructionCost RISCVTTIImpl::getCastInstrCost(unsigned Opcode, Type *Dst,
     return getRISCVInstructionCost(Op, DstLT.second, CostKind);
   }
   case ISD::TRUNCATE:
+    // Early return for invalid operation
+    if (Dst->getScalarSizeInBits() >= Src->getScalarSizeInBits())
+      break;
     if (Dst->getScalarSizeInBits() == 1) {
       // We do not use several vncvt to truncate to mask vector. So we could
       // not use PowDiff to calculate it.
@@ -968,6 +971,13 @@ InstructionCost RISCVTTIImpl::getCastInstrCost(unsigned Opcode, Type *Dst,
     [[fallthrough]];
   case ISD::FP_EXTEND:
   case ISD::FP_ROUND: {
+    // Early return for invalid operation
+    if ((ISD == ISD::FP_ROUND) &&
+        Dst->getScalarSizeInBits() >= Src->getScalarSizeInBits())
+      break;
+    if ((ISD == ISD::FP_EXTEND) &&
+        Src->getScalarSizeInBits() >= Dst->getScalarSizeInBits())
+      break;
     // Counts of narrow/widen instructions.
     unsigned SrcEltSize = Src->getScalarSizeInBits();
     unsigned DstEltSize = Dst->getScalarSizeInBits();