[PATCH] D127751: [MergeFunctions] Preserve symbols used llvm.used/llvm.compiler.used

[Amanieu d'Antras via Phabricator via llvm-commits]

Amanieu updated this revision to Diff 436814.
Amanieu added a comment.

Updated test.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D127751/new/

https://reviews.llvm.org/D127751

Files:
  llvm/lib/Transforms/IPO/MergeFunctions.cpp
  llvm/test/Transforms/MergeFunc/merge-used.ll


Index: llvm/test/Transforms/MergeFunc/merge-used.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/MergeFunc/merge-used.ll
@@ -0,0 +1,25 @@
+; RUN: opt -S -mergefunc < %s | FileCheck %s
+
+ at 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
+}
+
+; CHECK-LABEL: @llvm.compiler.used = appending global [2 x i8*] [i8* bitcast (i32 (i32)* @b to 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 internal i32 @a(i32 %0) unnamed_addr
+; CHECK-NEXT:    tail call i32 @b(i32 %0)
+; CHECK-NEXT:    ret
Index: llvm/lib/Transforms/IPO/MergeFunctions.cpp
===================================================================
--- llvm/lib/Transforms/IPO/MergeFunctions.cpp
+++ llvm/lib/Transforms/IPO/MergeFunctions.cpp
@@ -120,6 +120,7 @@
 #include "llvm/Support/raw_ostream.h"
 #include "llvm/Transforms/IPO.h"
 #include "llvm/Transforms/Utils/FunctionComparator.h"
+#include "llvm/Transforms/Utils/ModuleUtils.h"
 #include <algorithm>
 #include <cassert>
 #include <iterator>
@@ -225,6 +226,10 @@
   /// analyzed again.
   std::vector<WeakTrackingVH> Deferred;
 
+  /// Set of values marked as used in llvm.used and llvm.compiler.used.
+  SmallPtrSet<GlobalValue *, 4> Used;
+  SmallPtrSet<GlobalValue *, 4> CompilerUsed;
+
 #ifndef NDEBUG
   /// Checks the rules of order relation introduced among functions set.
   /// Returns true, if check has been passed, and false if failed.
@@ -407,6 +412,14 @@
 bool MergeFunctions::runOnModule(Module &M) {
   bool Changed = false;
 
+  // Keep track of functions referred to by llvm.used/llvm.compiler.used.
+  SmallVector<GlobalValue *, 4> UsedV;
+  collectUsedGlobalVariables(M, UsedV, /*CompilerUsed=*/false);
+  Used.insert(UsedV.begin(), UsedV.end());
+  SmallVector<GlobalValue *, 4> CompilerUsedV;
+  collectUsedGlobalVariables(M, CompilerUsedV, /*CompilerUsed=*/true);
+  CompilerUsed.insert(CompilerUsedV.begin(), CompilerUsedV.end());
+
   // All functions in the module, ordered by hash. Functions with a unique
   // hash value are easily eliminated.
   std::vector<std::pair<FunctionComparator::FunctionHash, Function *>>
@@ -453,6 +466,8 @@
   FnTree.clear();
   FNodesInTree.clear();
   GlobalNumbers.clear();
+  Used.clear();
+  CompilerUsed.clear();
 
   return Changed;
 }
@@ -833,6 +848,18 @@
         Constant *BitcastF = ConstantExpr::getBitCast(F, G->getType());
         removeUsers(G);
         G->replaceAllUsesWith(BitcastF);
+
+        // 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. We need to handle these by keeping the old
+        // symbol in the used list as an alias or thunk.
+        //
+        // RAUW will have removed references to G from the existing list, make
+        // sure to add it back.
+        if (Used.contains(G))
+          appendToUsed(*G->getParent(), {G});
+        if (CompilerUsed.contains(G))
+          appendToCompilerUsed(*G->getParent(), {G});
       } else {
         // Redirect direct callers of G to F. (See note on MergeFunctionsPDI
         // above).


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