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llvm-mirror/test/Bitcode/mdnodes-distinct-in-post-order.ll

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Add an index for Module Metadata record in the bitcode This index record the position for each metadata record in the bitcode, so that the reader will be able to lazy-load on demand each individual record. We also make sure that every abbrev is emitted upfront so that the block can be skipped while reading. I don't plan to commit this before having the reader counterpart, but I figured this can be reviewed mostly independently. Recommit r290684 (was reverted in r290686 because a test was broken) after adding a threshold to avoid emitting the index when unnecessary (little amount of metadata). This optimization "hides" a limitation of the ability to backpatch in the bitstream: we can only backpatch safely when the position has been flushed. So if we emit an index for one metadata, it is possible that (part of) the offset placeholder hasn't been flushed and the backpatch will fail. Differential Revision: https://reviews.llvm.org/D28083 llvm-svn: 290690
2016-12-28 23:30:28 +01:00
; RUN: llvm-as <%s -bitcode-mdindex-threshold=0 | llvm-bcanalyzer -dump | FileCheck %s -check-prefix=CHECK -check-prefix=MDINDEX
; RUN: llvm-as <%s | llvm-bcanalyzer -dump | FileCheck %s -check-prefix=CHECK
BitcodeWriter: Emit uniqued subgraphs after all distinct nodes Since forward references for uniqued node operands are expensive (and those for distinct node operands are cheap due to DistinctMDOperandPlaceholder), minimize forward references in uniqued node operands. Moreover, guarantee that when a cycle is broken by a distinct node, none of the uniqued nodes have any forward references. In ValueEnumerator::EnumerateMetadata, enumerate uniqued node subgraphs first, delaying distinct nodes until all uniqued nodes have been handled. This guarantees that uniqued nodes only have forward references when there is a uniquing cycle (since r267276 changed ValueEnumerator::organizeMetadata to partition distinct nodes in front of uniqued nodes as a post-pass). Note that a single uniqued subgraph can hit multiple distinct nodes at its leaves. Ideally these would themselves be emitted in post-order, but this commit doesn't attempt that; I think it requires an extra pass through the edges, which I'm not convinced is worth it (since DistinctMDOperandPlaceholder makes forward references quite cheap between distinct nodes). I've added two testcases: - test/Bitcode/mdnodes-distinct-in-post-order.ll is just like test/Bitcode/mdnodes-in-post-order.ll, except with distinct nodes instead of uniqued ones. This confirms that, in the absence of uniqued nodes, distinct nodes are still emitted in post-order. - test/Bitcode/mdnodes-distinct-nodes-break-cycles.ll is the minimal example where a naive post-order traversal would cause one uniqued node to forward-reference another. IOW, it's the motivating test. llvm-svn: 267278
2016-04-23 06:59:22 +02:00
; Check that distinct nodes are emitted in post-order to avoid unnecessary
; forward references.
; Nodes in this testcase are numbered to match how they are referenced in
; bitcode. !3 is referenced as opN=3.
; The leafs should come first (in either order).
; CHECK: <DISTINCT_NODE/>
; CHECK-NEXT: <DISTINCT_NODE/>
!1 = distinct !{}
!2 = distinct !{}
; CHECK-NEXT: <DISTINCT_NODE op0=1 op1=2/>
!3 = distinct !{!1, !2}
; CHECK-NEXT: <DISTINCT_NODE op0=1 op1=3 op2=2/>
!4 = distinct !{!1, !3, !2}
Add an index for Module Metadata record in the bitcode This index record the position for each metadata record in the bitcode, so that the reader will be able to lazy-load on demand each individual record. We also make sure that every abbrev is emitted upfront so that the block can be skipped while reading. I don't plan to commit this before having the reader counterpart, but I figured this can be reviewed mostly independently. Recommit r290684 (was reverted in r290686 because a test was broken) after adding a threshold to avoid emitting the index when unnecessary (little amount of metadata). This optimization "hides" a limitation of the ability to backpatch in the bitstream: we can only backpatch safely when the position has been flushed. So if we emit an index for one metadata, it is possible that (part of) the offset placeholder hasn't been flushed and the backpatch will fail. Differential Revision: https://reviews.llvm.org/D28083 llvm-svn: 290690
2016-12-28 23:30:28 +01:00
; Before the named records we emit the index containing the position of the
; previously emitted records, but only if we have a number of record above
; a threshold (can be controlled through `-bitcode-mdindex-threshold`).
; MDINDEX: <INDEX {{.*}} (offset match)
BitcodeWriter: Emit uniqued subgraphs after all distinct nodes Since forward references for uniqued node operands are expensive (and those for distinct node operands are cheap due to DistinctMDOperandPlaceholder), minimize forward references in uniqued node operands. Moreover, guarantee that when a cycle is broken by a distinct node, none of the uniqued nodes have any forward references. In ValueEnumerator::EnumerateMetadata, enumerate uniqued node subgraphs first, delaying distinct nodes until all uniqued nodes have been handled. This guarantees that uniqued nodes only have forward references when there is a uniquing cycle (since r267276 changed ValueEnumerator::organizeMetadata to partition distinct nodes in front of uniqued nodes as a post-pass). Note that a single uniqued subgraph can hit multiple distinct nodes at its leaves. Ideally these would themselves be emitted in post-order, but this commit doesn't attempt that; I think it requires an extra pass through the edges, which I'm not convinced is worth it (since DistinctMDOperandPlaceholder makes forward references quite cheap between distinct nodes). I've added two testcases: - test/Bitcode/mdnodes-distinct-in-post-order.ll is just like test/Bitcode/mdnodes-in-post-order.ll, except with distinct nodes instead of uniqued ones. This confirms that, in the absence of uniqued nodes, distinct nodes are still emitted in post-order. - test/Bitcode/mdnodes-distinct-nodes-break-cycles.ll is the minimal example where a naive post-order traversal would cause one uniqued node to forward-reference another. IOW, it's the motivating test. llvm-svn: 267278
2016-04-23 06:59:22 +02:00
; Note: named metadata nodes are not cannot reference null so their operands
; are numbered off-by-one.
; CHECK-NEXT: <NAME
; CHECK-NEXT: <NAMED_NODE op0=3/>
!named = !{!4}
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