From 87f312aad6ede636cd2de5d18f3058bf2caf5651 Mon Sep 17 00:00:00 2001 From: Matt Arsenault Date: Tue, 6 May 2025 17:20:37 +0200 Subject: IR: Remove uselist for constantdata (#137313) This is a resurrected version of the patch attached to this RFC: https://discourse.llvm.org/t/rfc-constantdata-should-not-have-use-lists/42606 In this adaptation, there are a few differences. In the original patch, the Use's use list was replaced with an unsigned* to the reference count in the value. This version leaves them as null and leaves the ref counting only in Value. Remove use-lists from instances of ConstantData (which are shared across modules and have no operands). To continue supporting most of the use-list API, store a ref-count in place of the use-list; this is for API like Value::use_empty and Value::hasNUses. Operations that actually need the use-list -- like Value::use_begin -- will assert. This change has three benefits: 1. The compiler output cannot in any way depend on the use-list order of instances of ConstantData. 2. There's no use-list traffic when adding and removing simple constants from operand lists (although there is ref-count traffic; YMMV). 3. It's cheaper to serialize use-lists (since we're no longer serializing the use-list order of things like i32 0). The downside is that you can't look at all the users of ConstantData, but traversals of users of i32 0 are already ill-advised. Possible follow-ups: - Track if an instance of a ConstantVector/ConstantArray/etc. is known to have all ConstantData arguments, and drop the use-lists to ref-counts in those cases. Callers need to check Value::hasUseList before iterating through the use-list. - Remove even the ref-counts. I'm not sure they have any benefit besides minimizing the scope of this commit, and maintaining the counts is not free. Fixes #58629 Co-authored-by: Duncan P. N. Exon Smith --- llvm/lib/Bitcode/Reader/BitcodeReader.cpp | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'llvm/lib/Bitcode/Reader/BitcodeReader.cpp') diff --git a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp index 4074ed65..e510320 100644 --- a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp +++ b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp @@ -3860,6 +3860,10 @@ Error BitcodeReader::parseUseLists() { V = FunctionBBs[ID]; } else V = ValueList[ID]; + + if (!V->hasUseList()) + break; + unsigned NumUses = 0; SmallDenseMap Order; for (const Use &U : V->materialized_uses()) { -- cgit v1.1