[llvm] Explain partial byte extraction logic. (PR #92868)

[Johannes Reifferscheid via llvm-commits]

https://github.com/jreiffers created https://github.com/llvm/llvm-project/pull/92868

This is a follow-up to #92506.

>From f7257bb9abb05a248b4e3d0fbc4a0b769cff2413 Mon Sep 17 00:00:00 2001
From: Johannes Reifferscheid <jreiffers at google.com>
Date: Tue, 21 May 2024 09:20:24 +0200
Subject: [PATCH] Explain partial byte extraction logic.

This is a follow-up to #92506.
---
 llvm/lib/Target/NVPTX/NVPTXAsmPrinter.cpp | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/llvm/lib/Target/NVPTX/NVPTXAsmPrinter.cpp b/llvm/lib/Target/NVPTX/NVPTXAsmPrinter.cpp
index f63697916d902..5c03ddb54c2b6 100644
--- a/llvm/lib/Target/NVPTX/NVPTXAsmPrinter.cpp
+++ b/llvm/lib/Target/NVPTX/NVPTXAsmPrinter.cpp
@@ -1851,6 +1851,9 @@ void NVPTXAsmPrinter::bufferLEByte(const Constant *CPV, int Bytes,
   auto AddIntToBuffer = [AggBuffer, Bytes](const APInt &Val) {
     size_t NumBytes = (Val.getBitWidth() + 7) / 8;
     SmallVector<unsigned char, 16> Buf(NumBytes);
+    // `extractBitsAsZExtValue` does not allow the extraction of bits beyond the
+    // input's bit width. We handle the last byte separately, so we never
+    // request out of bounds bits.
     for (unsigned I = 0; I < NumBytes - 1; ++I) {
       Buf[I] = Val.extractBitsAsZExtValue(8, I * 8);
     }