[GlobalOpt] Don't replace the aliasee if it has other references.

As long as aliasee has `@llvm.used` or `@llvm.compiler.used` references, we cannot do the related replace or delete operations. Even if it is a Local Linkage, we cannot infer if there is no other use for it, such as asm or other future added cases.

Reviewed By: nikic

Differential Revision: https://reviews.llvm.org/D145293

Author: dianqk

llvm/lib/Transforms/IPO/GlobalOpt.cpp

@@ -2219,22 +2219,11 @@ static bool hasUseOtherThanLLVMUsed(GlobalAlias &GA, const LLVMUsed &U) {
   return !U.usedCount(&GA) && !U.compilerUsedCount(&GA);
 }
 
-static bool hasMoreThanOneUseOtherThanLLVMUsed(GlobalValue &V,
-                                               const LLVMUsed &U) {
-  unsigned N = 2;
-  assert((!U.usedCount(&V) || !U.compilerUsedCount(&V)) &&
-         "We should have removed the duplicated "
-         "element from llvm.compiler.used");
-  if (U.usedCount(&V) || U.compilerUsedCount(&V))
-    ++N;
-  return V.hasNUsesOrMore(N);
-}
-
-static bool mayHaveOtherReferences(GlobalAlias &GA, const LLVMUsed &U) {
-  if (!GA.hasLocalLinkage())
+static bool mayHaveOtherReferences(GlobalValue &GV, const LLVMUsed &U) {
+  if (!GV.hasLocalLinkage())
     return true;
 
-  return U.usedCount(&GA) || U.compilerUsedCount(&GA);
+  return U.usedCount(&GV) || U.compilerUsedCount(&GV);
 }
 
 static bool hasUsesToReplace(GlobalAlias &GA, const LLVMUsed &U,
@@ -2248,21 +2237,16 @@ static bool hasUsesToReplace(GlobalAlias &GA, const LLVMUsed &U,
   if (!mayHaveOtherReferences(GA, U))
     return Ret;
 
-  // If the aliasee has internal linkage, give it the name and linkage
-  // of the alias, and delete the alias.  This turns:
+  // If the aliasee has internal linkage and no other references (e.g.,
+  // @llvm.used, @llvm.compiler.used), give it the name and linkage of the
+  // alias, and delete the alias. This turns:
   //   define internal ... @f(...)
   //   @a = alias ... @f
   // into:
   //   define ... @a(...)
   Constant *Aliasee = GA.getAliasee();
   GlobalValue *Target = cast<GlobalValue>(Aliasee->stripPointerCasts());
-  if (!Target->hasLocalLinkage())
-    return Ret;
-
-  // Do not perform the transform if multiple aliases potentially target the
-  // aliasee. This check also ensures that it is safe to replace the section
-  // and other attributes of the aliasee with those of the alias.
-  if (hasMoreThanOneUseOtherThanLLVMUsed(*Target, U))
+  if (mayHaveOtherReferences(*Target, U))
     return Ret;
 
   RenameTarget = true;

llvm/test/Transforms/GlobalOpt/X86/alias-used-with-asm.ll

@@ -0,0 +1,22 @@
+; RUN: opt < %s -passes=globalopt -S | FileCheck %s
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+module asm ".global foo1"
+module asm "foo1: jmp bar1"
+module asm ".global foo2"
+module asm "foo2: jmp bar2"
+
+; The `llvm.compiler.used` indicates that `foo1` and `foo2` have associated symbol references in asm.
+; Checking globalopt does not remove these two symbols.
+@llvm.compiler.used = appending global [2 x ptr] [ptr @bar1, ptr @bar2], section "llvm.metadata"
+; CHECK: @llvm.compiler.used = appending global [2 x ptr] [ptr @bar1, ptr @bar2], section "llvm.metadata"
+
+@bar2 = internal alias void (), ptr @bar1
+; CHECK: @bar2 = internal alias void (), ptr @bar1
+
+define internal void @bar1() {
+; CHECK: define internal void @bar1()
+  ret void
+}

llvm/test/Transforms/GlobalOpt/alias-used-address-space.ll

@@ -5,19 +5,20 @@ target datalayout = "p:32:32:32-p1:16:16:16"
 @c = hidden addrspace(1) global i8 42
 
 @i = internal addrspace(1) global i8 42
-
-; CHECK: @ia = internal addrspace(1) global i8 42
-@ia = internal alias i8, ptr addrspace(1) @i
+; CHECK: @i = internal addrspace(1) global i8 42
 
 @llvm.used = appending global [1 x ptr] [ptr addrspacecast (ptr addrspace(1) @ca to ptr)], section "llvm.metadata"
 ; CHECK-DAG: @llvm.used = appending global [1 x ptr] [ptr addrspacecast (ptr addrspace(1) @ca to ptr)], section "llvm.metadata"
 
 @llvm.compiler.used = appending global [2 x ptr] [ptr addrspacecast(ptr addrspace(1) @ia to ptr), ptr addrspacecast (ptr addrspace(1) @i to ptr)], section "llvm.metadata"
-; CHECK-DAG: @llvm.compiler.used = appending global [1 x ptr] [ptr addrspacecast (ptr addrspace(1) @ia to ptr)], section "llvm.metadata"
+; CHECK-DAG: @llvm.compiler.used = appending global [2 x ptr] [ptr addrspacecast (ptr addrspace(1) @i to ptr), ptr addrspacecast (ptr addrspace(1) @ia to ptr)], section "llvm.metadata"
 
 @sameAsUsed = global [1 x ptr] [ptr addrspacecast(ptr addrspace(1) @ca to ptr)]
 ; CHECK-DAG: @sameAsUsed = local_unnamed_addr global [1 x ptr] [ptr addrspacecast (ptr addrspace(1) @c to ptr)]
 
+@ia = internal alias i8, ptr addrspace(1) @i
+; CHECK: @ia = internal alias i8, ptr addrspace(1) @i
+
 @ca = internal alias i8, ptr addrspace(1) @c
 ; CHECK: @ca = internal alias i8, ptr addrspace(1) @c
 

llvm/test/Transforms/GlobalOpt/alias-used.ll

@@ -2,15 +2,16 @@
 
 @c = dso_local global i8 42
 
+; CHECK: @i = internal global i8 42
 @i = internal global i8 42
-; CHECK: @ia = internal global i8 42
+; CHECK-DAG: @ia = internal alias i8, ptr @i
 @ia = internal alias i8, ptr @i
 
 @llvm.used = appending global [3 x ptr] [ptr @fa, ptr @f, ptr @ca], section "llvm.metadata"
 ; CHECK-DAG: @llvm.used = appending global [3 x ptr] [ptr @ca, ptr @f, ptr @fa], section "llvm.metadata"
 
 @llvm.compiler.used = appending global [4 x ptr] [ptr @fa3, ptr @fa, ptr @ia, ptr @i], section "llvm.metadata"
-; CHECK-DAG: @llvm.compiler.used = appending global [2 x ptr] [ptr @fa3, ptr @ia], section "llvm.metadata"
+; CHECK-DAG: @llvm.compiler.used = appending global [3 x ptr] [ptr @fa3, ptr @i, ptr @ia], section "llvm.metadata"
 
 @sameAsUsed = global [3 x ptr] [ptr @fa, ptr @f, ptr @ca]
 ; CHECK-DAG: @sameAsUsed = local_unnamed_addr global [3 x ptr] [ptr @f, ptr @f, ptr @c]

polly/test/Support/dumpfunction.ll

@@ -20,8 +20,6 @@
 
 %unrelated_type = type { i32 }
 
-@callee_alias = dso_local unnamed_addr alias void(i32, ptr, i32), ptr @callee
-
 define internal void @callee(i32 %n, ptr noalias nonnull %A, i32 %i) #0 {
 entry:
   br label %for