[clang] (New) Add option to generate additional debug info for expression dereferencing pointer to pointers (PR #95298)
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Wed Jun 12 12:49:06 PDT 2024
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-clang-codegen
Author: William Junda Huang (huangjd)
<details>
<summary>Changes</summary>
This is a different implementation to #<!-- -->94100, which has been reverted.
When -fdebug-info-for-profiling is specified, for any Load expression if the pointer operand is not a declared variable, clang will emit debug info describing the type of the pointer operand (which can be an intermediate expr)
---
Full diff: https://github.com/llvm/llvm-project/pull/95298.diff
4 Files Affected:
- (modified) clang/lib/CodeGen/CGDebugInfo.cpp (+51)
- (modified) clang/lib/CodeGen/CGDebugInfo.h (+6)
- (modified) clang/lib/CodeGen/CGExprScalar.cpp (+20-1)
- (added) clang/test/CodeGenCXX/debug-info-ptr-to-ptr.cpp (+115)
``````````diff
diff --git a/clang/lib/CodeGen/CGDebugInfo.cpp b/clang/lib/CodeGen/CGDebugInfo.cpp
index 99e12da0081af..d3b754d14b19e 100644
--- a/clang/lib/CodeGen/CGDebugInfo.cpp
+++ b/clang/lib/CodeGen/CGDebugInfo.cpp
@@ -5746,6 +5746,57 @@ void CGDebugInfo::EmitExternalVariable(llvm::GlobalVariable *Var,
Var->addDebugInfo(GVE);
}
+void CGDebugInfo::EmitPseudoVariable(CGBuilderTy &Builder,
+ llvm::Instruction *Value, QualType Ty) {
+ // Only when -g2 or above is specified, debug info for variables will be
+ // generated.
+ if (CGM.getCodeGenOpts().getDebugInfo() <=
+ llvm::codegenoptions::DebugLineTablesOnly)
+ return;
+
+ llvm::DILocation *DIL = Value->getDebugLoc().get();
+ if (!DIL)
+ return;
+
+ llvm::DIFile *Unit = DIL->getFile();
+ llvm::DIType *Type = getOrCreateType(Ty, Unit);
+
+ // Check if Value is already a declared variable and has debug info, in this
+ // case we have nothing to do. Clang emits declared variable as alloca, and
+ // it is loaded upon use, so we identify such pattern here.
+ if (llvm::LoadInst *Load = dyn_cast<llvm::LoadInst>(Value)) {
+ llvm::Value *Var = Load->getPointerOperand();
+ // There can be implicit type cast applied on a variable if it is an opaque
+ // ptr, in this case its debug info may not match the actual type of object
+ // being used as in the next instruction, so we will need to emit a pseudo
+ // variable for type-casted value.
+ auto DeclareTypeMatches = [&](auto *DbgDeclare) {
+ return DbgDeclare->getVariable()->getType() == Type;
+ };
+ if (any_of(llvm::findDbgDeclares(Var), DeclareTypeMatches) ||
+ any_of(llvm::findDVRDeclares(Var), DeclareTypeMatches))
+ return;
+ }
+
+ // Find the correct location to insert the debug value.
+ llvm::BasicBlock *InsertBB = Value->getParent();
+ llvm::Instruction *InsertBefore = Value->getIterator()->getNextNode();
+ if (llvm::InvokeInst *Invoke = dyn_cast<llvm::InvokeInst>(Value)) {
+ InsertBB = Invoke->getNormalDest();
+ InsertBefore = InsertBB->size() > 0 ? &(InsertBB->front()) : nullptr;
+ }
+
+ llvm::DILocalVariable *D = DBuilder.createAutoVariable(
+ LexicalBlockStack.back(), "", nullptr, 0, Type, false,
+ llvm::DINode::FlagArtificial);
+ if (InsertBefore)
+ DBuilder.insertDbgValueIntrinsic(Value, D, DBuilder.createExpression(), DIL,
+ InsertBefore);
+ else
+ DBuilder.insertDbgValueIntrinsic(Value, D, DBuilder.createExpression(), DIL,
+ InsertBB);
+}
+
void CGDebugInfo::EmitGlobalAlias(const llvm::GlobalValue *GV,
const GlobalDecl GD) {
diff --git a/clang/lib/CodeGen/CGDebugInfo.h b/clang/lib/CodeGen/CGDebugInfo.h
index 8fe738be21568..da466837aa3c3 100644
--- a/clang/lib/CodeGen/CGDebugInfo.h
+++ b/clang/lib/CodeGen/CGDebugInfo.h
@@ -530,6 +530,12 @@ class CGDebugInfo {
/// Emit information about an external variable.
void EmitExternalVariable(llvm::GlobalVariable *GV, const VarDecl *Decl);
+ /// Emit a pseudo variable and debug info for an intermediate value if it does
+ /// not correspond to a variable in the source code, so that a profiler can
+ /// track more accurate usage of certain instructions of interest.
+ void EmitPseudoVariable(CGBuilderTy &Builder, llvm::Instruction *Value,
+ QualType Ty);
+
/// Emit information about global variable alias.
void EmitGlobalAlias(const llvm::GlobalValue *GV, const GlobalDecl Decl);
diff --git a/clang/lib/CodeGen/CGExprScalar.cpp b/clang/lib/CodeGen/CGExprScalar.cpp
index 1b144c178ce96..58f0a3113b4f8 100644
--- a/clang/lib/CodeGen/CGExprScalar.cpp
+++ b/clang/lib/CodeGen/CGExprScalar.cpp
@@ -1937,7 +1937,26 @@ Value *ScalarExprEmitter::VisitMemberExpr(MemberExpr *E) {
}
}
- return EmitLoadOfLValue(E);
+ llvm::Value *Result = EmitLoadOfLValue(E);
+
+ // If -fdebug-info-for-profiling is specified, emit a pseudo variable and its
+ // debug info for the pointer, even if there is no variable associated with
+ // the pointer's expression.
+ if (CGF.CGM.getCodeGenOpts().DebugInfoForProfiling && CGF.getDebugInfo()) {
+ if (llvm::LoadInst *Load = dyn_cast<llvm::LoadInst>(Result)) {
+ if (llvm::GetElementPtrInst *GEP =
+ dyn_cast<llvm::GetElementPtrInst>(Load->getPointerOperand())) {
+ if (llvm::Instruction *Pointer =
+ dyn_cast<llvm::Instruction>(GEP->getPointerOperand())) {
+ QualType Ty = E->getBase()->getType();
+ if (!E->isArrow())
+ Ty = CGF.getContext().getPointerType(Ty);
+ CGF.getDebugInfo()->EmitPseudoVariable(Builder, Pointer, Ty);
+ }
+ }
+ }
+ }
+ return Result;
}
Value *ScalarExprEmitter::VisitArraySubscriptExpr(ArraySubscriptExpr *E) {
diff --git a/clang/test/CodeGenCXX/debug-info-ptr-to-ptr.cpp b/clang/test/CodeGenCXX/debug-info-ptr-to-ptr.cpp
new file mode 100644
index 0000000000000..51ce0f107b5e3
--- /dev/null
+++ b/clang/test/CodeGenCXX/debug-info-ptr-to-ptr.cpp
@@ -0,0 +1,115 @@
+// Test debug info for intermediate value of a chained pointer deferencing
+// expression when the flag -fdebug-info-for-pointer-type is enabled.
+// RUN: %clang_cc1 -emit-llvm -triple x86_64-linux-gnu %s -fdebug-info-for-profiling -debug-info-kind=constructor -o - | FileCheck %s
+
+class A {
+public:
+ int i;
+ char c;
+ void *p;
+ int arr[3];
+};
+
+class B {
+public:
+ A* a;
+};
+
+class C {
+public:
+ B* b;
+ A* a;
+ A arr[10];
+};
+
+// CHECK-LABEL: define dso_local noundef i32 @{{.*}}func1{{.*}}(
+// CHECK: [[A_ADDR:%.*]] = getelementptr inbounds %class.B, ptr {{%.*}}, i32 0, i32 0, !dbg [[DBG1:![0-9]+]]
+// CHECK-NEXT: [[A:%.*]] = load ptr, ptr [[A_ADDR]], align {{.*}}, !dbg [[DBG1]]
+// CHECK-NEXT: call void @llvm.dbg.value(metadata ptr [[A]], metadata [[META1:![0-9]+]], metadata !DIExpression()), !dbg [[DBG1]]
+// CHECK-NEXT: {{%.*}} = getelementptr inbounds %class.A, ptr [[A]], i32 0, i32 0,
+int func1(B *b) {
+ return b->a->i;
+}
+
+// Should generate a pseudo variable when pointer is type-casted.
+// CHECK-LABEL: define dso_local noundef ptr @{{.*}}func2{{.*}}(
+// CHECK: call void @llvm.dbg.declare(metadata ptr [[B_ADDR:%.*]], metadata [[META2:![0-9]+]], metadata !DIExpression())
+// CHECK-NEXT: [[B:%.*]] = load ptr, ptr [[B_ADDR]],
+// CHECK-NEXT: call void @llvm.dbg.value(metadata ptr [[B]], metadata [[META3:![0-9]+]], metadata !DIExpression())
+// CHECK-NEXT: {{%.*}} = getelementptr inbounds %class.B, ptr [[B]], i32 0,
+A* func2(void *b) {
+ return ((B*)b)->a;
+}
+
+// Should not generate pseudo variable in this case.
+// CHECK-LABEL: define dso_local noundef i32 @{{.*}}func3{{.*}}(
+// CHECK: call void @llvm.dbg.declare(metadata ptr [[B_ADDR:%.*]], metadata [[META4:![0-9]+]], metadata !DIExpression())
+// CHECK: call void @llvm.dbg.declare(metadata ptr [[LOCAL1:%.*]], metadata [[META5:![0-9]+]], metadata !DIExpression())
+// CHECK-NOT: call void @llvm.dbg.value(metadata ptr
+int func3(B *b) {
+ A *local1 = b->a;
+ return local1->i;
+}
+
+// CHECK-LABEL: define dso_local noundef signext i8 @{{.*}}func4{{.*}}(
+// CHECK: [[A_ADDR:%.*]] = getelementptr inbounds %class.C, ptr {{%.*}}, i32 0, i32 1
+// CHECK-NEXT: [[A:%.*]] = load ptr, ptr [[A_ADDR]],
+// CHECK-NEXT: call void @llvm.dbg.value(metadata ptr [[A]], metadata [[META6:![0-9]+]], metadata !DIExpression())
+// CHECK-NEXT: {{%.*}} = getelementptr inbounds %class.A, ptr [[A]], i32 0, i32 0,
+// CHECK: [[CALL:%.*]] = call noundef ptr @{{.*}}foo{{.*}}(
+// CHECK-NEXT: call void @llvm.dbg.value(metadata ptr [[CALL]], metadata [[META6]], metadata !DIExpression())
+// CHECK-NEXT: [[I1:%.*]] = getelementptr inbounds %class.A, ptr [[CALL]], i32 0, i32 1
+char func4(C *c) {
+ extern A* foo(int x);
+ return foo(c->a->i)->c;
+}
+
+// CHECK-LABEL: define dso_local noundef signext i8 @{{.*}}func5{{.*}}(
+// CHECK: call void @llvm.dbg.declare(metadata ptr {{%.*}}, metadata [[META7:![0-9]+]], metadata !DIExpression())
+// CHECK: call void @llvm.dbg.declare(metadata ptr {{%.*}}, metadata [[META8:![0-9]+]], metadata !DIExpression())
+// CHECK: [[A_ADDR:%.*]] = getelementptr inbounds %class.A, ptr {{%.*}}, i64 {{%.*}},
+// CHECK-NEXT: call void @llvm.dbg.value(metadata ptr [[A_ADDR]], metadata [[META9:![0-9]+]], metadata !DIExpression())
+// CHECK-NEXT: {{%.*}} = getelementptr inbounds %class.A, ptr [[A_ADDR]], i32 0, i32 1,
+char func5(void *arr, int n) {
+ return ((A*)arr)[n].c;
+}
+
+// CHECK-LABEL: define dso_local noundef i32 @{{.*}}func6{{.*}}(
+// CHECK: call void @llvm.dbg.declare(metadata ptr {{%.*}}, metadata [[META10:![0-9]+]], metadata !DIExpression())
+// CHECK: call void @llvm.dbg.value(metadata ptr {{%.*}}, metadata [[META11:![0-9]+]], metadata !DIExpression())
+int func6(B &b) {
+ return reinterpret_cast<A&>(b).i;
+}
+
+// CHECK-LABEL: define dso_local noundef i32 @{{.*}}global{{.*}}(
+// CHECK: [[GA:%.*]] = load ptr, ptr @ga
+// CHECK-NEXT: call void @llvm.dbg.value(metadata ptr [[GA]], metadata [[META12:![0-9]+]], metadata !DIExpression())
+A *ga;
+int global() {
+ return ga->i;
+}
+
+
+// CHECK-DAG: [[META_A:![0-9]+]] = distinct !DICompositeType(tag: DW_TAG_class_type, name: "A",
+// CHECK-DAG: [[META_AP:![0-9]+]] = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: [[META_A]],
+// CHECK-DAG: [[META_B:![0-9]+]] = distinct !DICompositeType(tag: DW_TAG_class_type, name: "B",
+// CHECK-DAG: [[META_BP:![0-9]+]] = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: [[META_B]],
+// CHECK-DAG: [[META_C:![0-9]+]] = distinct !DICompositeType(tag: DW_TAG_class_type, name: "C",
+// CHECK-DAG: [[META_CP:![0-9]+]] = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: [[META_C]],
+// CHECK-DAG: [[META_VP:![0-9]+]] = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: null,
+// CHECK-DAG: [[META_I32:![0-9]+]] = !DIBasicType(name: "int", size: 32,
+// CHECK-DAG: [[META_BR:![0-9]+]] = !DIDerivedType(tag: DW_TAG_reference_type, baseType: [[META_B]],
+
+// CHECK-DAG: [[DBG1]] = !DILocation(line: 31, column: 13,
+// CHECK-DAG: [[META1]] = !DILocalVariable(scope: {{.*}}, type: [[META_AP]], flags: DIFlagArtificial)
+// CHECK-DAG: [[META2]] = !DILocalVariable(name: "b", arg: 1, scope: {{.*}}, file: {{.*}}, line: 40, type: [[META_VP]])
+// CHECK-DAG: [[META3]] = !DILocalVariable(scope: {{.*}}, type: [[META_BP]], flags: DIFlagArtificial)
+// CHECK-DAG: [[META4]] = !DILocalVariable(name: "b", arg: 1, scope: {{.*}}, file: {{.*}}, line: 49, type: [[META_BP]])
+// CHECK-DAG: [[META5]] = !DILocalVariable(name: "local1", scope: {{.*}}, file: {{.*}}, line: 50, type: [[META_AP]])
+// CHECK-DAG: [[META6]] = !DILocalVariable(scope: {{.*}}, type: [[META_AP]], flags: DIFlagArtificial)
+// CHECK-DAG: [[META7]] = !DILocalVariable(name: "arr", arg: 1, scope: {{.*}}, file: {{.*}}, line: 73, type: [[META_VP]])
+// CHECK-DAG: [[META8]] = !DILocalVariable(name: "n", arg: 2, scope: {{.*}}, file: {{.*}}, line: 73, type: [[META_I32]])
+// CHECK-DAG: [[META9]] = !DILocalVariable(scope: {{.*}}, type: [[META_AP]], flags: DIFlagArtificial)
+// CHECK-DAG: [[META10]] = !DILocalVariable(name: "b", arg: 1, scope: {{.*}}, file: {{.*}}, line: 80, type: [[META_BR]])
+// CHECK-DAG: [[META11]] = !DILocalVariable(scope: {{.*}}, type: [[META_AP]], flags: DIFlagArtificial)
+// CHECK-DAG: [[META12]] = !DILocalVariable(scope: {{.*}}, type: [[META_AP]], flags: DIFlagArtificial)
``````````
</details>
https://github.com/llvm/llvm-project/pull/95298
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