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Fix crash or wrong code bug if a lifetime-extended temporary contains a 

"non-constant" value.

If the constant evaluator evaluates part of a variable initializer,
including the initializer for some lifetime-extended temporary, but
fails to fully evaluate the initializer, it can leave behind wrong
values for temporaries encountered in that initialization. Don't try to
emit those from CodeGen! Instead, look at the values that constant
evaluation produced if (and only if) it actually succeeds and we're
emitting the lifetime-extending declaration's initializer as a constant.

llvm-svn: 374119
This commit is contained in:
Richard Smith 2019-10-08 21:26:03 +00:00
parent f61f13d4e7
commit 48632af25c
3 changed files with 28 additions and 9 deletions
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6
clang/lib/AST/ExprConstant.cpp
View File

@ -13569,8 +13569,10 @@ bool Expr::EvaluateAsConstantExpr(EvalResult &Result, ConstExprUsage Usage,
if (!Info.discardCleanups()) if (!Info.discardCleanups())
llvm_unreachable("Unhandled cleanup; missing full expression marker?"); llvm_unreachable("Unhandled cleanup; missing full expression marker?");
return CheckConstantExpression(Info, getExprLoc(), getType(), Result.Val, QualType T = getType();
Usage) && if (!isRValue())
T = Ctx.getLValueReferenceType(T);
return CheckConstantExpression(Info, getExprLoc(), T, Result.Val, Usage) &&
CheckMemoryLeaks(Info); CheckMemoryLeaks(Info);
} }

13
clang/lib/CodeGen/CodeGenModule.cpp
View File

@ -4978,14 +4978,13 @@ ConstantAddress CodeGenModule::GetAddrOfGlobalTemporary(
VD, E->getManglingNumber(), Out); VD, E->getManglingNumber(), Out);
APValue *Value = nullptr; APValue *Value = nullptr;
if (E->getStorageDuration() == SD_Static) { if (E->getStorageDuration() == SD_Static && VD && VD->evaluateValue()) {
// We might have a cached constant initializer for this temporary. Note // If the initializer of the extending declaration is a constant
// that this might have a different value from the value computed by // initializer, we should have a cached constant initializer for this
// evaluating the initializer if the surrounding constant expression // temporary. Note that this might have a different value from the value
// modifies the temporary. // computed by evaluating the initializer if the surrounding constant
// expression modifies the temporary.
Value = getContext().getMaterializedTemporaryValue(E, false); Value = getContext().getMaterializedTemporaryValue(E, false);
if (Value && Value->isAbsent())
Value = nullptr;
} }
// Try evaluating it now, it might have a constant initializer. // Try evaluating it now, it might have a constant initializer.

18
clang/test/CodeGenCXX/no-const-init-cxx2a.cpp Normal file
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@ -0,0 +1,18 @@
// RUN: %clang_cc1 -triple x86_64-linux-gnu -emit-llvm -o - %s -std=c++2a | FileCheck %s
// CHECK-DAG: @p = {{.*}} null
// CHECK-DAG: @_ZGR1p_ = {{.*}} null
int *const &p = new int;
struct d {
constexpr d(int &&f) : e(f) {}
int &e;
};
// CHECK-DAG: @g = {{.*}} null
// CHECK-DAG: @_ZGR1g_ = {{.*}} zeroinitializer
d &&g{{0}};
// CHECK: define {{.*}} @__cxx_global_var_init
// CHECK: define {{.*}} @__cxx_global_var_init
// CHECK-NOT: define {{.*}} @__cxx_global_var_init