[GlobalOpt] Replace aliasee if it is not in use

Author: dianqk

llvm/lib/Transforms/IPO/GlobalOpt.cpp

@@ -2215,6 +2215,17 @@ 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(GlobalValue &GV, const LLVMUsed &U) {
   if (!GV.hasLocalLinkage())
     return true;
@@ -2224,9 +2235,6 @@ static bool mayHaveOtherReferences(GlobalValue &GV, const LLVMUsed &U) {
 
 static bool hasUsesToReplace(GlobalAlias &GA, const LLVMUsed &U,
                              bool &RenameTarget) {
-  if (GA.isWeakForLinker())
-    return false;
-
   RenameTarget = false;
   bool Ret = false;
   if (hasUseOtherThanLLVMUsed(GA, U))
@@ -2245,6 +2253,13 @@ static bool hasUsesToReplace(GlobalAlias &GA, const LLVMUsed &U,
   //   define ... @a(...)
   Constant *Aliasee = GA.getAliasee();
   GlobalValue *Target = cast<GlobalValue>(Aliasee->stripPointerCasts());
+  // Don't perform the transform if the alias may be replaced at link time while
+  // someone is using the aliasee (e.g., multiple aliases potentially target it
+  // or someone calls it).
+  if (GA.isWeakForLinker())
+    Ret = false;
+  if (hasMoreThanOneUseOtherThanLLVMUsed(*Target, U))
+    return Ret;
   if (mayHaveOtherReferences(*Target, U))
     return Ret;
 

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

@@ -25,13 +25,12 @@ define internal void @f1() {
   ret void
 }
 
-; FIXME: We can use `f2_alias` to replace `f2` because `b2` is not in use.
+; We can use `f2_alias` to replace `f2` because `b2` is not in use.
 define internal void @f2() {
   ret void
 }
 ;.
 ; CHECK: @f1_alias = linkonce_odr hidden alias void (), ptr @f1
-; CHECK: @f2_alias = linkonce_odr hidden alias void (), ptr @f2
 ;.
 ; CHECK-LABEL: define void @foo() local_unnamed_addr {
 ; CHECK-NEXT:    call void @f1_alias()
@@ -52,6 +51,6 @@ define internal void @f2() {
 ; CHECK-NEXT:    ret void
 ;
 ;
-; CHECK-LABEL: define internal void @f2() {
+; CHECK-LABEL: define linkonce_odr hidden void @f2_alias() local_unnamed_addr {
 ; CHECK-NEXT:    ret void
 ;

llvm/test/Transforms/LowerTypeTests/cfi-nounwind-direct-call.ll

@@ -121,7 +121,7 @@ attributes #6 = { noreturn nounwind }
 ; CHECK-LABEL: define dso_local noundef range(i32 0, 2) i32 @_Z10call_catchi
 ; CHECK-SAME: (i32 noundef [[NUM:%.*]]) local_unnamed_addr #[[ATTR1:[0-9]+]] !type [[META4]] !type [[META5]] !type [[META6]] {
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    store ptr @_Z9nothrow_ei.cfi_jt, ptr @catch_ptr, align 8, !tbaa [[TBAA7:![0-9]+]]
+; CHECK-NEXT:    store ptr @.cfi.jumptable, ptr @catch_ptr, align 8, !tbaa [[TBAA7:![0-9]+]]
 ; CHECK-NEXT:    [[TOBOOL_NOT_I:%.*]] = icmp ne i32 [[NUM]], 0
 ; CHECK-NEXT:    [[DOT_I:%.*]] = zext i1 [[TOBOOL_NOT_I]] to i32
 ; CHECK-NEXT:    ret i32 [[DOT_I]]
@@ -152,7 +152,7 @@ attributes #6 = { noreturn nounwind }
 ;
 ;
 ; CHECK: Function Attrs: naked nocf_check noinline nounwind
-; CHECK-LABEL: define internal void @_Z9nothrow_ei.cfi_jt
+; CHECK-LABEL: define private void @.cfi.jumptable
 ; CHECK-SAME: () #[[ATTR5:[0-9]+]] align 8 {
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    tail call void asm sideeffect "jmp ${0:c}@plt\0Aint3\0Aint3\0Aint3\0A", "s"(ptr nonnull @_Z9nothrow_ei) #[[ATTR7:[0-9]+]]

llvm/test/Transforms/LowerTypeTests/cfi-unwind-direct-call.ll

@@ -174,8 +174,8 @@ attributes #8 = { noreturn nounwind }
 ; CHECK-LABEL: define dso_local void @_Z10call_catchi(
 ; CHECK-SAME: i32 noundef [[NUM:%.*]]) local_unnamed_addr #[[ATTR0]] personality ptr @__gxx_personality_v0 !type [[META4]] !type [[META5]] !type [[META6]] {
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    store ptr @_Z7throw_ei.cfi_jt, ptr @catch_ptr, align 8, !tbaa [[TBAA11:![0-9]+]]
-; CHECK-NEXT:    invoke void @_Z7throw_ei.cfi_jt(i32 noundef [[NUM]]) #[[ATTR8:[0-9]+]]
+; CHECK-NEXT:    store ptr @.cfi.jumptable, ptr @catch_ptr, align 8, !tbaa [[TBAA11:![0-9]+]]
+; CHECK-NEXT:    invoke void @.cfi.jumptable(i32 noundef [[NUM]]) #[[ATTR8:[0-9]+]]
 ; CHECK-NEXT:            to label [[TRY_CONT:%.*]] unwind label [[LPAD:%.*]], !callees [[META13:![0-9]+]]
 ; CHECK:       lpad:
 ; CHECK-NEXT:    [[TMP0:%.*]] = landingpad { ptr, i32 }
@@ -220,7 +220,7 @@ attributes #8 = { noreturn nounwind }
 ;
 ;
 ; CHECK: Function Attrs: naked nocf_check noinline
-; CHECK-LABEL: define internal void @_Z7throw_ei.cfi_jt(
+; CHECK-LABEL: define private void @.cfi.jumptable(
 ; CHECK-SAME: ) #[[ATTR5:[0-9]+]] align 8 {
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    tail call void asm sideeffect "jmp ${0:c}@plt\0Aint3\0Aint3\0Aint3\0A", "s"(ptr nonnull @_Z7throw_ei) #[[ATTR6]]
@@ -236,6 +236,6 @@ attributes #8 = { noreturn nounwind }
 ; CHECK: [[META10]] = !{!"Simple C++ TBAA"}
 ; CHECK: [[TBAA11]] = !{[[META12:![0-9]+]], [[META12]], i64 0}
 ; CHECK: [[META12]] = !{!"any pointer", [[META9]], i64 0}
-; CHECK: [[META13]] = !{ptr @_Z7throw_ei.cfi_jt}
+; CHECK: [[META13]] = !{ptr @.cfi.jumptable}
 ; CHECK: [[META14]] = !{}
 ;.