[llvm] WholeProgramDevirt: Always import/export constants directly in the summary (PR #188979)
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Fri Mar 27 05:17:56 PDT 2026
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-lto
Author: Hans Wennborg (zmodem)
<details>
<summary>Changes</summary>
rather than using absolute symbol constants on ELF/x86.
This leads to better codegen as the absolute symbol constants were not resolved until link time (see bug for example).
It also simplifies the code by having a single code path for all targets.
Fixes #<!-- -->188470
---
Full diff: https://github.com/llvm/llvm-project/pull/188979.diff
3 Files Affected:
- (modified) llvm/lib/Transforms/IPO/WholeProgramDevirt.cpp (+4-64)
- (modified) llvm/test/Transforms/WholeProgramDevirt/export-vcp.ll (+9-17)
- (modified) llvm/test/Transforms/WholeProgramDevirt/import.ll (+7-21)
``````````diff
diff --git a/llvm/lib/Transforms/IPO/WholeProgramDevirt.cpp b/llvm/lib/Transforms/IPO/WholeProgramDevirt.cpp
index 019b5ee6ac2f9..c19856f0b2daa 100644
--- a/llvm/lib/Transforms/IPO/WholeProgramDevirt.cpp
+++ b/llvm/lib/Transforms/IPO/WholeProgramDevirt.cpp
@@ -696,23 +696,16 @@ struct DevirtModule {
std::string getGlobalName(VTableSlot Slot, ArrayRef<uint64_t> Args,
StringRef Name);
- bool shouldExportConstantsAsAbsoluteSymbols();
-
// This function is called during the export phase to create a symbol
// definition containing information about the given vtable slot and list of
// arguments.
void exportGlobal(VTableSlot Slot, ArrayRef<uint64_t> Args, StringRef Name,
Constant *C);
- void exportConstant(VTableSlot Slot, ArrayRef<uint64_t> Args, StringRef Name,
- uint32_t Const, uint32_t &Storage);
// This function is called during the import phase to create a reference to
// the symbol definition created during the export phase.
Constant *importGlobal(VTableSlot Slot, ArrayRef<uint64_t> Args,
StringRef Name);
- Constant *importConstant(VTableSlot Slot, ArrayRef<uint64_t> Args,
- StringRef Name, IntegerType *IntTy,
- uint32_t Storage);
Constant *getMemberAddr(const TypeMemberInfo *M);
@@ -1735,11 +1728,6 @@ std::string DevirtModule::getGlobalName(VTableSlot Slot,
return FullName;
}
-bool DevirtModule::shouldExportConstantsAsAbsoluteSymbols() {
- Triple T(M.getTargetTriple());
- return T.isX86() && T.getObjectFormat() == Triple::ELF;
-}
-
void DevirtModule::exportGlobal(VTableSlot Slot, ArrayRef<uint64_t> Args,
StringRef Name, Constant *C) {
GlobalAlias *GA = GlobalAlias::create(Int8Ty, 0, GlobalValue::ExternalLinkage,
@@ -1747,19 +1735,6 @@ void DevirtModule::exportGlobal(VTableSlot Slot, ArrayRef<uint64_t> Args,
GA->setVisibility(GlobalValue::HiddenVisibility);
}
-void DevirtModule::exportConstant(VTableSlot Slot, ArrayRef<uint64_t> Args,
- StringRef Name, uint32_t Const,
- uint32_t &Storage) {
- if (shouldExportConstantsAsAbsoluteSymbols()) {
- exportGlobal(
- Slot, Args, Name,
- ConstantExpr::getIntToPtr(ConstantInt::get(Int32Ty, Const), Int8PtrTy));
- return;
- }
-
- Storage = Const;
-}
-
Constant *DevirtModule::importGlobal(VTableSlot Slot, ArrayRef<uint64_t> Args,
StringRef Name) {
GlobalVariable *GV =
@@ -1768,37 +1743,6 @@ Constant *DevirtModule::importGlobal(VTableSlot Slot, ArrayRef<uint64_t> Args,
return GV;
}
-Constant *DevirtModule::importConstant(VTableSlot Slot, ArrayRef<uint64_t> Args,
- StringRef Name, IntegerType *IntTy,
- uint32_t Storage) {
- if (!shouldExportConstantsAsAbsoluteSymbols())
- return ConstantInt::get(IntTy, Storage);
-
- Constant *C = importGlobal(Slot, Args, Name);
- auto *GV = cast<GlobalVariable>(C->stripPointerCasts());
- C = ConstantExpr::getPtrToInt(C, IntTy);
-
- // We only need to set metadata if the global is newly created, in which
- // case it would not have hidden visibility.
- if (GV->hasMetadata(LLVMContext::MD_absolute_symbol))
- return C;
-
- auto SetAbsRange = [&](uint64_t Min, uint64_t Max) {
- auto *MinC = ConstantAsMetadata::get(ConstantInt::get(IntPtrTy, Min));
- auto *MaxC = ConstantAsMetadata::get(ConstantInt::get(IntPtrTy, Max));
- GV->setMetadata(LLVMContext::MD_absolute_symbol,
- MDNode::get(M.getContext(), {MinC, MaxC}));
- };
- unsigned AbsWidth = IntTy->getBitWidth();
- if (AbsWidth == IntPtrTy->getBitWidth()) {
- uint64_t AllOnes = IntTy->getBitMask();
- SetAbsRange(AllOnes, AllOnes); // Full set.
- } else {
- SetAbsRange(0, 1ull << AbsWidth);
- }
- return C;
-}
-
void DevirtModule::applyUniqueRetValOpt(CallSiteInfo &CSInfo, StringRef FnName,
bool IsOne,
Constant *UniqueMemberAddr) {
@@ -2026,10 +1970,8 @@ bool DevirtModule::tryVirtualConstProp(
if (CSByConstantArg.second.isExported()) {
ResByArg->TheKind = WholeProgramDevirtResolution::ByArg::VirtualConstProp;
- exportConstant(Slot, CSByConstantArg.first, "byte", OffsetByte,
- ResByArg->Byte);
- exportConstant(Slot, CSByConstantArg.first, "bit", 1ULL << OffsetBit,
- ResByArg->Bit);
+ ResByArg->Byte = OffsetByte;
+ ResByArg->Bit = 1ULL << OffsetBit;
}
// Rewrite each call to a load from OffsetByte/OffsetBit.
@@ -2309,10 +2251,8 @@ void DevirtModule::importResolution(VTableSlot Slot, VTableSlotInfo &SlotInfo) {
break;
}
case WholeProgramDevirtResolution::ByArg::VirtualConstProp: {
- Constant *Byte = importConstant(Slot, CSByConstantArg.first, "byte",
- Int32Ty, ResByArg.Byte);
- Constant *Bit = importConstant(Slot, CSByConstantArg.first, "bit", Int8Ty,
- ResByArg.Bit);
+ Constant *Byte = ConstantInt::get(Int32Ty, ResByArg.Byte);
+ Constant *Bit = ConstantInt::get(Int8Ty, ResByArg.Bit);
applyVirtualConstProp(CSByConstantArg.second, "", Byte, Bit);
break;
}
diff --git a/llvm/test/Transforms/WholeProgramDevirt/export-vcp.ll b/llvm/test/Transforms/WholeProgramDevirt/export-vcp.ll
index 24aba548ea9ac..cc02a0668a2f1 100644
--- a/llvm/test/Transforms/WholeProgramDevirt/export-vcp.ll
+++ b/llvm/test/Transforms/WholeProgramDevirt/export-vcp.ll
@@ -1,8 +1,8 @@
-; RUN: opt -mtriple=x86_64-unknown-linux-gnu -passes=wholeprogramdevirt -whole-program-visibility -wholeprogramdevirt-summary-action=export -wholeprogramdevirt-read-summary=%S/Inputs/export.yaml -wholeprogramdevirt-write-summary=%t -S -o - %s | FileCheck --check-prefixes=CHECK,X86 %s
-; RUN: FileCheck --check-prefixes=SUMMARY,SUMMARY-X86 %s < %t
+; RUN: opt -mtriple=x86_64-unknown-linux-gnu -passes=wholeprogramdevirt -whole-program-visibility -wholeprogramdevirt-summary-action=export -wholeprogramdevirt-read-summary=%S/Inputs/export.yaml -wholeprogramdevirt-write-summary=%t -S -o - %s | FileCheck --check-prefixes=CHECK %s
+; RUN: FileCheck --check-prefixes=SUMMARY %s < %t
-; RUN: opt -mtriple=armv7-unknown-linux-gnu -passes=wholeprogramdevirt -whole-program-visibility -wholeprogramdevirt-summary-action=export -wholeprogramdevirt-read-summary=%S/Inputs/export.yaml -wholeprogramdevirt-write-summary=%t -S -o - %s | FileCheck --check-prefixes=CHECK,ARM %s
-; RUN: FileCheck --check-prefixes=SUMMARY,SUMMARY-ARM %s < %t
+; RUN: opt -mtriple=armv7-unknown-linux-gnu -passes=wholeprogramdevirt -whole-program-visibility -wholeprogramdevirt-summary-action=export -wholeprogramdevirt-read-summary=%S/Inputs/export.yaml -wholeprogramdevirt-write-summary=%t -S -o - %s | FileCheck --check-prefixes=CHECK %s
+; RUN: FileCheck --check-prefixes=SUMMARY %s < %t
target datalayout = "e-p:64:64"
@@ -23,10 +23,8 @@ target datalayout = "e-p:64:64"
; SUMMARY-NEXT: 12,24:
; SUMMARY-NEXT: Kind: VirtualConstProp
; SUMMARY-NEXT: Info: 0
-; SUMMARY-X86-NEXT: Byte: 0
-; SUMMARY-X86-NEXT: Bit: 0
-; SUMMARY-ARM-NEXT: Byte: 4294967295
-; SUMMARY-ARM-NEXT: Bit: 1
+; SUMMARY-NEXT: Byte: 4294967295
+; SUMMARY-NEXT: Bit: 1
; SUMMARY-NEXT: typeid4:
; SUMMARY-NEXT: TTRes:
; SUMMARY-NEXT: Kind: Unknown
@@ -43,10 +41,8 @@ target datalayout = "e-p:64:64"
; SUMMARY-NEXT: 24,12:
; SUMMARY-NEXT: Kind: VirtualConstProp
; SUMMARY-NEXT: Info: 0
-; SUMMARY-X86-NEXT: Byte: 0
-; SUMMARY-X86-NEXT: Bit: 0
-; SUMMARY-ARM-NEXT: Byte: 4294967292
-; SUMMARY-ARM-NEXT: Bit: 1
+; SUMMARY-NEXT: Byte: 4294967292
+; SUMMARY-NEXT: Bit: 1
; CHECK: [[CVT3A:.*]] = private constant { [8 x i8], ptr, [0 x i8] } { [8 x i8] zeroinitializer, ptr @vf0i1, [0 x i8] zeroinitializer }, !type !0
@vt3a = constant ptr @vf0i1, !type !0
@@ -66,11 +62,7 @@ target datalayout = "e-p:64:64"
; CHECK: [[CVT4B:.*]] = private constant { [8 x i8], ptr, [0 x i8] } { [8 x i8] c"\00\00\00\00\02\00\00\00", ptr @vf2i32, [0 x i8] zeroinitializer }, !type !1
@vt4b = constant ptr @vf2i32, !type !1
-; X86: @__typeid_typeid3_0_12_24_byte = hidden alias i8, inttoptr (i32 -1 to ptr)
-; X86: @__typeid_typeid3_0_12_24_bit = hidden alias i8, inttoptr (i32 1 to ptr)
-; X86: @__typeid_typeid4_0_24_12_byte = hidden alias i8, inttoptr (i32 -4 to ptr)
-; X86: @__typeid_typeid4_0_24_12_bit = hidden alias i8, inttoptr (i32 1 to ptr)
-; ARM-NOT: alias {{.*}} inttoptr
+; CHECK-NOT: alias {{.*}} inttoptr
; CHECK: @vt3a = alias ptr, getelementptr inbounds ({ [8 x i8], ptr, [0 x i8] }, ptr [[CVT3A]], i32 0, i32 1)
; CHECK: @vt3b = alias ptr, getelementptr inbounds ({ [8 x i8], ptr, [0 x i8] }, ptr [[CVT3B]], i32 0, i32 1)
diff --git a/llvm/test/Transforms/WholeProgramDevirt/import.ll b/llvm/test/Transforms/WholeProgramDevirt/import.ll
index 812ffbdf7f3fb..7f843c87e5098 100644
--- a/llvm/test/Transforms/WholeProgramDevirt/import.ll
+++ b/llvm/test/Transforms/WholeProgramDevirt/import.ll
@@ -2,20 +2,15 @@
; RUN: opt -S -passes=wholeprogramdevirt -wholeprogramdevirt-summary-action=import -wholeprogramdevirt-read-summary=%S/Inputs/import-uniform-ret-val.yaml < %s | FileCheck --check-prefixes=CHECK,INDIR,UNIFORM-RET-VAL %s
; RUN: opt -S -passes=wholeprogramdevirt -wholeprogramdevirt-summary-action=import -wholeprogramdevirt-read-summary=%S/Inputs/import-unique-ret-val0.yaml < %s | FileCheck --check-prefixes=CHECK,INDIR,UNIQUE-RET-VAL0 %s
; RUN: opt -S -passes=wholeprogramdevirt -wholeprogramdevirt-summary-action=import -wholeprogramdevirt-read-summary=%S/Inputs/import-unique-ret-val1.yaml < %s | FileCheck --check-prefixes=CHECK,INDIR,UNIQUE-RET-VAL1 %s
-; RUN: opt -S -passes=wholeprogramdevirt -wholeprogramdevirt-summary-action=import -wholeprogramdevirt-read-summary=%S/Inputs/import-vcp.yaml < %s | FileCheck --check-prefixes=CHECK,VCP,VCP-X86,VCP64,INDIR %s
-; RUN: opt -S -passes=wholeprogramdevirt -wholeprogramdevirt-summary-action=import -wholeprogramdevirt-read-summary=%S/Inputs/import-vcp.yaml -mtriple=i686-unknown-linux -data-layout=e-p:32:32 < %s | FileCheck --check-prefixes=CHECK,VCP,VCP-X86,VCP32 %s
-; RUN: opt -S -passes=wholeprogramdevirt -wholeprogramdevirt-summary-action=import -wholeprogramdevirt-read-summary=%S/Inputs/import-vcp.yaml -mtriple=armv7-unknown-linux -data-layout=e-p:32:32 < %s | FileCheck --check-prefixes=CHECK,VCP,VCP-ARM %s
-; RUN: opt -S -passes=wholeprogramdevirt -wholeprogramdevirt-summary-action=import -wholeprogramdevirt-read-summary=%S/Inputs/import-vcp-branch-funnel.yaml < %s | FileCheck --check-prefixes=CHECK,VCP,VCP-X86,VCP64,BRANCH-FUNNEL %s
+; RUN: opt -S -passes=wholeprogramdevirt -wholeprogramdevirt-summary-action=import -wholeprogramdevirt-read-summary=%S/Inputs/import-vcp.yaml < %s | FileCheck --check-prefixes=CHECK,VCP,INDIR %s
+; RUN: opt -S -passes=wholeprogramdevirt -wholeprogramdevirt-summary-action=import -wholeprogramdevirt-read-summary=%S/Inputs/import-vcp.yaml -mtriple=i686-unknown-linux -data-layout=e-p:32:32 < %s | FileCheck --check-prefixes=CHECK,VCP %s
+; RUN: opt -S -passes=wholeprogramdevirt -wholeprogramdevirt-summary-action=import -wholeprogramdevirt-read-summary=%S/Inputs/import-vcp.yaml -mtriple=armv7-unknown-linux -data-layout=e-p:32:32 < %s | FileCheck --check-prefixes=CHECK,VCP %s
+; RUN: opt -S -passes=wholeprogramdevirt -wholeprogramdevirt-summary-action=import -wholeprogramdevirt-read-summary=%S/Inputs/import-vcp-branch-funnel.yaml < %s | FileCheck --check-prefixes=CHECK,VCP,BRANCH-FUNNEL %s
; RUN: opt -S -passes=wholeprogramdevirt -wholeprogramdevirt-summary-action=import -wholeprogramdevirt-read-summary=%S/Inputs/import-branch-funnel.yaml < %s | FileCheck --check-prefixes=CHECK,BRANCH-FUNNEL,BRANCH-FUNNEL-NOVCP %s
target datalayout = "e-p:64:64"
target triple = "x86_64-unknown-linux-gnu"
-; VCP-X86: @__typeid_typeid1_0_1_byte = external hidden global [0 x i8], !absolute_symbol !0
-; VCP-X86: @__typeid_typeid1_0_1_bit = external hidden global [0 x i8], !absolute_symbol !1
-; VCP-X86: @__typeid_typeid2_8_3_byte = external hidden global [0 x i8], !absolute_symbol !0
-; VCP-X86: @__typeid_typeid2_8_3_bit = external hidden global [0 x i8], !absolute_symbol !1
-
; Test cases where the argument values are known and we can apply virtual
; constant propagation.
@@ -28,8 +23,7 @@ define i32 @call1(ptr %obj) #0 {
; SINGLE-IMPL: call i32 @singleimpl1
%result = call i32 %fptr(ptr %obj, i32 1)
; UNIFORM-RET-VAL: ret i32 42
- ; VCP-X86: [[GEP1:%.*]] = getelementptr i8, ptr %vtable, i32 ptrtoint (ptr @__typeid_typeid1_0_1_byte to i32)
- ; VCP-ARM: [[GEP1:%.*]] = getelementptr i8, ptr %vtable, i32 42
+ ; VCP: [[GEP1:%.*]] = getelementptr i8, ptr %vtable, i32 42
; VCP: [[LOAD1:%.*]] = load i32, ptr [[GEP1]]
; VCP: ret i32 [[LOAD1]]
; BRANCH-FUNNEL-NOVCP: call i32 @__typeid_typeid1_0_branch_funnel(ptr nest %vtable, ptr %obj, i32 1)
@@ -72,11 +66,9 @@ cont:
%result = call i1 %fptr(ptr %obj, i32 3)
; UNIQUE-RET-VAL0: icmp ne ptr %vtable, @__typeid_typeid2_8_3_unique_member
; UNIQUE-RET-VAL1: icmp eq ptr %vtable, @__typeid_typeid2_8_3_unique_member
- ; VCP-X86: [[GEP2:%.*]] = getelementptr i8, ptr %vtable, i32 ptrtoint (ptr @__typeid_typeid2_8_3_byte to i32)
- ; VCP-ARM: [[GEP2:%.*]] = getelementptr i8, ptr %vtable, i32 43
+ ; VCP: [[GEP2:%.*]] = getelementptr i8, ptr %vtable, i32 43
; VCP: [[LOAD2:%.*]] = load i8, ptr [[GEP2]]
- ; VCP-X86: [[AND2:%.*]] = and i8 [[LOAD2]], ptrtoint (ptr @__typeid_typeid2_8_3_bit to i8)
- ; VCP-ARM: [[AND2:%.*]] = and i8 [[LOAD2]], -128
+ ; VCP: [[AND2:%.*]] = and i8 [[LOAD2]], -128
; VCP: [[ICMP2:%.*]] = icmp ne i8 [[AND2]], 0
; VCP: ret i1 [[ICMP2]]
; BRANCH-FUNNEL-NOVCP: call i1 @__typeid_typeid2_8_branch_funnel(ptr nest %vtable, ptr %obj, i32 3)
@@ -90,12 +82,6 @@ trap:
; SINGLE-IMPL-DAG: declare void @singleimpl1()
; SINGLE-IMPL-DAG: declare void @singleimpl2()
-; VCP32: !0 = !{i32 -1, i32 -1}
-; VCP64: !0 = !{i64 0, i64 4294967296}
-
-; VCP32: !1 = !{i32 0, i32 256}
-; VCP64: !1 = !{i64 0, i64 256}
-
declare void @llvm.assume(i1)
declare void @llvm.trap()
declare {ptr, i1} @llvm.type.checked.load(ptr, i32, metadata)
``````````
</details>
https://github.com/llvm/llvm-project/pull/188979
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