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[GlobalOpt] Don't replace aliasee with alias that has weak linkage #91483

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Merged
merged 4 commits into from
May 16, 2024
Merged

[GlobalOpt] Don't replace aliasee with alias that has weak linkage #91483

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937ab67
Pre-commit test cases
dianqk May 9, 2024
ab7be41
[GlobalOpt] Don't replace aliasee with alias that has weak linkage
dianqk May 8, 2024
b901a98
[GlobalOpt] Replace aliasee if it is not in use
dianqk May 9, 2024
b4660c7
Revert "[GlobalOpt] Replace aliasee if it is not in use"
dianqk May 16, 2024
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18 changes: 18 additions & 0 deletions llvm/lib/Transforms/IPO/GlobalOpt.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -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;
Expand Down Expand Up @@ -2242,6 +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))
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Since there's a stripPointerCasts() earlier, do we need to check for other uses of a cast ConstantExpr, in addition to other uses of the global itself?

Or maybe we can just drop the whole pointer-cast-stripping thing... with opaque pointer types, not sure if there's any legitimate cast that can show up here. (An addressspacecast would be allowed by the verifier, but not sure it's something we can actually generate code for.)

return Ret;
if (mayHaveOtherReferences(*Target, U))
return Ret;

Expand Down
56 changes: 56 additions & 0 deletions llvm/test/Transforms/GlobalOpt/alias-weak.ll
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@@ -0,0 +1,56 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --check-globals all --include-generated-funcs --version 4
; RUN: opt < %s -passes=globalopt -S | FileCheck %s

@f1_alias = linkonce_odr hidden alias void (), ptr @f1
@f2_alias = linkonce_odr hidden alias void (), ptr @f2

define void @foo() {
call void @f1_alias()
ret void
}

define void @bar() {
call void @f1()
ret void
}

define void @baz() {
call void @f2_alias()
ret void
}

; We cannot use `f1_alias` to replace `f1` because they are both in use
; and `f1_alias` could be replaced at link time.
define internal void @f1() {
ret void
}

; 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-LABEL: define void @foo() local_unnamed_addr {
; CHECK-NEXT: call void @f1_alias()
; CHECK-NEXT: ret void
;
;
; CHECK-LABEL: define void @bar() local_unnamed_addr {
; CHECK-NEXT: call void @f1()
; CHECK-NEXT: ret void
;
;
; CHECK-LABEL: define void @baz() local_unnamed_addr {
; CHECK-NEXT: call void @f2_alias()
; CHECK-NEXT: ret void
;
;
; CHECK-LABEL: define internal void @f1() {
; CHECK-NEXT: ret void
;
;
; CHECK-LABEL: define linkonce_odr hidden void @f2_alias() local_unnamed_addr {
; CHECK-NEXT: ret void
;
4 changes: 2 additions & 2 deletions llvm/test/Transforms/LowerTypeTests/cfi-nounwind-direct-call.ll
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Expand Up @@ -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]]
Expand Down Expand Up @@ -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]+]]
Expand Down
8 changes: 4 additions & 4 deletions llvm/test/Transforms/LowerTypeTests/cfi-unwind-direct-call.ll
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Expand Up @@ -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 }
Expand Down Expand Up @@ -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]]
Expand All @@ -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]] = !{}
;.