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

[Johannes Reifferscheid via llvm-commits]

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

>From d2809a8474e7f80d6a4489e69af23861ed05f63c 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 | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/llvm/lib/Target/NVPTX/NVPTXAsmPrinter.cpp b/llvm/lib/Target/NVPTX/NVPTXAsmPrinter.cpp
index f63697916d902..c30368a60c126 100644
--- a/llvm/lib/Target/NVPTX/NVPTXAsmPrinter.cpp
+++ b/llvm/lib/Target/NVPTX/NVPTXAsmPrinter.cpp
@@ -1851,6 +1851,10 @@ 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, and i1 arrays may not have a length that is a multuple
+    // of 8. 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);
     }