[llvm] [AMDGPU] Do not use APInt for simple 64-bit arithmetic. NFC. (PR #109414)

[Jay Foad via llvm-commits]

https://github.com/jayfoad created https://github.com/llvm/llvm-project/pull/109414

None

>From cb76e9a505c957a5ec002c34a789eaa68a6fa3e5 Mon Sep 17 00:00:00 2001
From: Jay Foad <jay.foad at amd.com>
Date: Fri, 20 Sep 2024 13:25:30 +0100
Subject: [PATCH] [AMDGPU] Do not use APInt for simple 64-bit arithmetic. NFC.

---
 .../lib/Target/AMDGPU/Disassembler/AMDGPUDisassembler.cpp | 6 ++----
 llvm/lib/Target/AMDGPU/SIInstrInfo.cpp                    | 8 ++++----
 2 files changed, 6 insertions(+), 8 deletions(-)

diff --git a/llvm/lib/Target/AMDGPU/Disassembler/AMDGPUDisassembler.cpp b/llvm/lib/Target/AMDGPU/Disassembler/AMDGPUDisassembler.cpp
index 6c2a6643e67c76..2f5eba47afc27f 100644
--- a/llvm/lib/Target/AMDGPU/Disassembler/AMDGPUDisassembler.cpp
+++ b/llvm/lib/Target/AMDGPU/Disassembler/AMDGPUDisassembler.cpp
@@ -106,10 +106,8 @@ static DecodeStatus decodeSOPPBrTarget(MCInst &Inst, unsigned Imm,
                                        const MCDisassembler *Decoder) {
   auto DAsm = static_cast<const AMDGPUDisassembler*>(Decoder);
 
-  // Our branches take a simm16, but we need two extra bits to account for the
-  // factor of 4.
-  APInt SignedOffset(18, Imm * 4, true);
-  int64_t Offset = (SignedOffset.sext(64) + 4 + Addr).getSExtValue();
+  // Our branches take a simm16.
+  int64_t Offset = SignExtend64<16>(Imm) * 4 + 4 + Addr;
 
   if (DAsm->tryAddingSymbolicOperand(Inst, Offset, Addr, true, 2, 2, 0))
     return MCDisassembler::Success;
diff --git a/llvm/lib/Target/AMDGPU/SIInstrInfo.cpp b/llvm/lib/Target/AMDGPU/SIInstrInfo.cpp
index c6a9a627d457e7..f2de8bab6397d2 100644
--- a/llvm/lib/Target/AMDGPU/SIInstrInfo.cpp
+++ b/llvm/lib/Target/AMDGPU/SIInstrInfo.cpp
@@ -3401,13 +3401,13 @@ bool SIInstrInfo::foldImmediate(MachineInstr &UseMI, MachineInstr &DefMI,
     case AMDGPU::sub1:
       return Hi_32(Imm);
     case AMDGPU::lo16:
-      return APInt(16, Imm).getSExtValue();
+      return SignExtend64<16>(Imm);
     case AMDGPU::hi16:
-      return APInt(32, Imm).ashr(16).getSExtValue();
+      return SignExtend64<16>(Imm >> 16);
     case AMDGPU::sub1_lo16:
-      return APInt(16, Hi_32(Imm)).getSExtValue();
+      return SignExtend64<16>(Imm >> 32);
     case AMDGPU::sub1_hi16:
-      return APInt(32, Hi_32(Imm)).ashr(16).getSExtValue();
+      return SignExtend64<16>(Imm >> 48);
     }
   };