From 2cdf8f7c0bdc4d36f236e4cbb45bd9f996f15d14 Mon Sep 17 00:00:00 2001 From: Amanieu d'Antras Date: Thu, 16 Jun 2022 21:31:33 +0100 Subject: [PATCH 1/8] [MergeFunctions] Preserve symbols used llvm.used/llvm.compiler.used llvm.used and llvm.compiler.used are often used with inline assembly that refers to a specific symbol so that the symbol is kept through to the linker even though there are no references to it from LLVM IR. This fixes the MergeFunctions pass to preserve references to these symbols in llvm.used/llvm.compiler.used so they are not deleted from the IR. This doesn't prevent these functions from being merged, but guarantees that an alias or thunk with the expected symbol name is kept in the IR. Differential Revision: https://reviews.llvm.org/D127751 (cherry picked from commit caa2a829cdf905a5e8664d96a464d414b2adb42e) --- llvm/lib/Transforms/IPO/MergeFunctions.cpp | 15 ++++++++- llvm/test/Transforms/MergeFunc/merge-used.ll | 35 ++++++++++++++++++++ 2 files changed, 49 insertions(+), 1 deletion(-) create mode 100644 llvm/test/Transforms/MergeFunc/merge-used.ll diff --git a/llvm/lib/Transforms/IPO/MergeFunctions.cpp b/llvm/lib/Transforms/IPO/MergeFunctions.cpp index 97ef872c5499..b51e0a5d4dce 100644 --- a/llvm/lib/Transforms/IPO/MergeFunctions.cpp +++ b/llvm/lib/Transforms/IPO/MergeFunctions.cpp @@ -123,6 +123,7 @@ #include "llvm/Transforms/IPO.h" #include "llvm/Transforms/IPO/MergeFunctions.h" #include "llvm/Transforms/Utils/FunctionComparator.h" +#include "llvm/Transforms/Utils/ModuleUtils.h" #include #include #include @@ -228,6 +229,9 @@ private: /// analyzed again. std::vector Deferred; + /// Set of values marked as used in llvm.used and llvm.compiler.used. + SmallPtrSet Used; + #ifndef NDEBUG /// Checks the rules of order relation introduced among functions set. /// Returns true, if sanity check has been passed, and false if failed. @@ -410,6 +414,11 @@ static bool isEligibleForMerging(Function &F) { bool MergeFunctions::runOnModule(Module &M) { bool Changed = false; + SmallVector UsedV; + collectUsedGlobalVariables(M, UsedV, /*CompilerUsed=*/false); + collectUsedGlobalVariables(M, UsedV, /*CompilerUsed=*/true); + Used.insert(UsedV.begin(), UsedV.end()); + // All functions in the module, ordered by hash. Functions with a unique // hash value are easily eliminated. std::vector> @@ -456,6 +465,7 @@ bool MergeFunctions::runOnModule(Module &M) { FnTree.clear(); FNodesInTree.clear(); GlobalNumbers.clear(); + Used.clear(); return Changed; } @@ -828,7 +838,10 @@ void MergeFunctions::mergeTwoFunctions(Function *F, Function *G) { // For better debugability, under MergeFunctionsPDI, we do not modify G's // call sites to point to F even when within the same translation unit. if (!G->isInterposable() && !MergeFunctionsPDI) { - if (G->hasGlobalUnnamedAddr()) { + // Functions referred to by llvm.used/llvm.compiler.used are special: + // there are uses of the symbol name that are not visible to LLVM, + // usually from inline asm. + if (G->hasGlobalUnnamedAddr() && !Used.contains(G)) { // G might have been a key in our GlobalNumberState, and it's illegal // to replace a key in ValueMap with a non-global. GlobalNumbers.erase(G); diff --git a/llvm/test/Transforms/MergeFunc/merge-used.ll b/llvm/test/Transforms/MergeFunc/merge-used.ll new file mode 100644 index 000000000000..a86e66eee3f9 --- /dev/null +++ b/llvm/test/Transforms/MergeFunc/merge-used.ll @@ -0,0 +1,35 @@ +; RUN: opt -S -mergefunc < %s | FileCheck %s + +@llvm.compiler.used = appending global [1 x i8*] [i8* bitcast (i32 (i32)* @a to i8*)], section "llvm.metadata" + +define internal i32 @a(i32 %a) unnamed_addr { + %b = xor i32 %a, 0 + %c = xor i32 %b, 0 + ret i32 %c +} + +define i32 @b(i32 %a) unnamed_addr { + %b = xor i32 %a, 0 + %c = xor i32 %b, 0 + ret i32 %c +} + +define i32 @c(i32 %a) unnamed_addr { + %b = tail call i32 @a(i32 %a) + ret i32 %b +} + +; CHECK-LABEL: @llvm.compiler.used = appending global [1 x i8*] [i8* bitcast (i32 (i32)* @a to i8*)], section "llvm.metadata" + +; CHECK-LABEL: define i32 @b(i32 %a) unnamed_addr +; CHECK-NEXT: xor +; CHECK-NEXT: xor +; CHECK-NEXT: ret + +; CHECK-LABEL: define i32 @c(i32 %a) unnamed_addr +; CHECK-NEXT: tail call i32 @b(i32 %a) +; CHECK-NEXT: ret + +; CHECK-LABEL: define internal i32 @a(i32 %0) unnamed_addr +; CHECK-NEXT: tail call i32 @b(i32 %0) +; CHECK-NEXT: ret -- 2.37.0 (Apple Git-136)