From 2c74fe977daf8d1d4c8b64cdd6d3a9999a4b4655 Mon Sep 17 00:00:00 2001 From: Dan Gohman Date: Wed, 8 Nov 2017 21:59:51 +0000 Subject: Add an @llvm.sideeffect intrinsic This patch implements Chandler's idea [0] for supporting languages that require support for infinite loops with side effects, such as Rust, providing part of a solution to bug 965 [1]. Specifically, it adds an `llvm.sideeffect()` intrinsic, which has no actual effect, but which appears to optimization passes to have obscure side effects, such that they don't optimize away loops containing it. It also teaches several optimization passes to ignore this intrinsic, so that it doesn't significantly impact optimization in most cases. As discussed on llvm-dev [2], this patch is the first of two major parts. The second part, to change LLVM's semantics to have defined behavior on infinite loops by default, with a function attribute for opting into potential-undefined-behavior, will be implemented and posted for review in a separate patch. [0] http://lists.llvm.org/pipermail/llvm-dev/2015-July/088103.html [1] https://bugs.llvm.org/show_bug.cgi?id=965 [2] http://lists.llvm.org/pipermail/llvm-dev/2017-October/118632.html Differential Revision: https://reviews.llvm.org/D38336 llvm-svn: 317729 --- llvm/lib/Analysis/AliasSetTracker.cpp | 1 + 1 file changed, 1 insertion(+) (limited to 'llvm/lib/Analysis/AliasSetTracker.cpp') diff --git a/llvm/lib/Analysis/AliasSetTracker.cpp b/llvm/lib/Analysis/AliasSetTracker.cpp index 025e8119deb..b575944092a 100644 --- a/llvm/lib/Analysis/AliasSetTracker.cpp +++ b/llvm/lib/Analysis/AliasSetTracker.cpp @@ -436,6 +436,7 @@ void AliasSetTracker::addUnknown(Instruction *Inst) { break; // FIXME: Add lifetime/invariant intrinsics (See: PR30807). case Intrinsic::assume: + case Intrinsic::sideeffect: return; } } -- cgit v1.2.3