From 98bfdac5ce82d1679f8af9a57501471812ab68d7 Mon Sep 17 00:00:00 2001 From: Nikita Popov Date: Thu, 9 Nov 2023 10:23:10 +0100 Subject: [PATCH] [BranchFolding] Remove dubious assert from operator< (#71639) `MergePotentialElts::operator<` asserts that the two elements being compared are not equal. However, sorting functions are allowed to invoke the comparison function with equal arguments (though they usually don't for efficiency reasons). There is an existing special-case that disables the assert if _GLIBCXX_DEBUG is used, which may invoke the comparator with equal args to verify strict weak ordering. I believe libc++ also has strict weak ordering checks under some options nowadays. Recently, #71312 was reported, where a change to glibc's qsort_r implementation can also result in comparison between equal elements. From what I understood, this is an inefficiency that will be fixed on the glibc side as well, but I think at this point we should just remove this assertion. Fixes https://github.com/llvm/llvm-project/issues/71312. (cherry picked from commit 74a76a288562c486f377121855ef7db0386e0e43) --- llvm/lib/CodeGen/BranchFolding.cpp | 6 ------ 1 file changed, 6 deletions(-) diff --git a/llvm/lib/CodeGen/BranchFolding.cpp b/llvm/lib/CodeGen/BranchFolding.cpp index 3830f25debaf3..0801296cab49f 100644 --- a/llvm/lib/CodeGen/BranchFolding.cpp +++ b/llvm/lib/CodeGen/BranchFolding.cpp @@ -485,13 +485,7 @@ BranchFolder::MergePotentialsElt::operator<(const MergePotentialsElt &o) const { return true; if (getBlock()->getNumber() > o.getBlock()->getNumber()) return false; - // _GLIBCXX_DEBUG checks strict weak ordering, which involves comparing - // an object with itself. -#ifndef _GLIBCXX_DEBUG - llvm_unreachable("Predecessor appears twice"); -#else return false; -#endif } /// CountTerminators - Count the number of terminators in the given