From 7148abc1b900555199998aac25af11783a9eb41c Mon Sep 17 00:00:00 2001 From: Austin Clements Date: Fri, 5 Jun 2020 16:44:29 -0400 Subject: [PATCH] runtime: simplify heapBitsSetType doubleCheck The heapBitsSetType function has a slow doubleCheck debugging mode that checks the bitmap written out by the rest of the function using far more obvious logic. But even this has some surprisingly complex logic in it. Simplify it a bit. This also happens to fix the logic on 32-bit. Fixes #40335. Change-Id: I5cee482ad8adbd01cf5b98e35a270fe941ba4940 Reviewed-on: https://go-review.googlesource.com/c/go/+/244538 Run-TryBot: Austin Clements TryBot-Result: Gobot Gobot Reviewed-by: Michael Knyszek --- src/runtime/mbitmap.go | 28 ++++++++++++++++------------ 1 file changed, 16 insertions(+), 12 deletions(-) diff --git a/src/runtime/mbitmap.go b/src/runtime/mbitmap.go index 35332c91c4..cad6f56404 100644 --- a/src/runtime/mbitmap.go +++ b/src/runtime/mbitmap.go @@ -1403,17 +1403,20 @@ Phase4: // Double check the whole bitmap. if doubleCheck { // x+size may not point to the heap, so back up one - // word and then call next(). - end := heapBitsForAddr(x + size - sys.PtrSize).next() - endAI := arenaIdx(end.arena) - if !outOfPlace && (end.bitp == nil || (end.shift == 0 && end.bitp == &mheap_.arenas[endAI.l1()][endAI.l2()].bitmap[0])) { - // The unrolling code above walks hbitp just - // past the bitmap without moving to the next - // arena. Synthesize this for end.bitp. - end.arena-- - endAI = arenaIdx(end.arena) - end.bitp = addb(&mheap_.arenas[endAI.l1()][endAI.l2()].bitmap[0], heapArenaBitmapBytes) - end.last = nil + // word and then advance it the way we do above. + end := heapBitsForAddr(x + size - sys.PtrSize) + if outOfPlace { + // In out-of-place copying, we just advance + // using next. + end = end.next() + } else { + // Don't use next because that may advance to + // the next arena and the in-place logic + // doesn't do that. + end.shift += heapBitsShift + if end.shift == 4*heapBitsShift { + end.bitp, end.shift = add1(end.bitp), 0 + } } if typ.kind&kindGCProg == 0 && (hbitp != end.bitp || (w == nw+2) != (end.shift == 2)) { println("ended at wrong bitmap byte for", typ.string(), "x", dataSize/typ.size) @@ -1437,8 +1440,9 @@ Phase4: var have, want uint8 have = (*h.bitp >> h.shift) & (bitPointer | bitScan) if i >= totalptr { - want = 0 // deadmarker if typ.kind&kindGCProg != 0 && i < (totalptr+3)/4*4 { + // heapBitsSetTypeGCProg always fills + // in full nibbles of bitScan. want = bitScan } } else { -- 2.48.1