Explain partial byte extraction logic.

[jreiffers]

This is a follow-up to #92506.

[Artem-B]

LGTM with a nit.

[Artem-B]

beyond the input's bit width

... and i1 arrays may not be in multiples of 8.

That was the missing piece for me. With that in mind, the code could be simplified to iterate over all bytes, but do extractBitsAsZExtValue(min(remaining bits, 8),...), without special-casing the last byte.

[jreiffers]

Done. Sorry for the delay.

[llvmbot]

@llvm/pr-subscribers-backend-nvptx

Author: Johannes Reifferscheid (jreiffers)

Changes

This is a follow-up to #92506.

---

Full diff: https://github.com/llvm/llvm-project/pull/92868.diff

1 Files Affected:

• (modified) llvm/lib/Target/NVPTX/NVPTXAsmPrinter.cpp (+4)

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);
     }