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[clang] Add size filter for stack auto init (#74777)
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Add a clang flag, "-ftrivial-auto-var-init-max-size=" so that clang
skips auto-init a variable if the auto-init memset size exceeds the flag
setting (in bytes). Note that this skipping doesn't apply to
runtime-sized variables like VLA.

Considerations: "__attribute__((uninitialized))" can be used to manually
opt variables out. However, there are thousands of large variables
(e.g., >=1KB, most of them are arrays and used as buffers) in big
codebase. Manually opting them out one by one is not efficient.
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@haopliu
haopliu authored Jan 18, 2024
1 parent fa6c3df commit a58ad3e
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7 changes: 7 additions & 0 deletions clang/include/clang/Basic/DiagnosticDriverKinds.td
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Expand Up @@ -656,6 +656,13 @@ def err_drv_trivial_auto_var_init_stop_after_missing_dependency : Error<
def err_drv_trivial_auto_var_init_stop_after_invalid_value : Error<
"'-ftrivial-auto-var-init-stop-after=*' only accepts positive integers">;

def err_drv_trivial_auto_var_init_max_size_missing_dependency : Error<
"'-ftrivial-auto-var-init-max-size=*' is used without "
"'-ftrivial-auto-var-init=zero' or '-ftrivial-auto-var-init=pattern'">;

def err_drv_trivial_auto_var_init_max_size_invalid_value : Error<
"'-ftrivial-auto-var-init-max-size=*' only accepts positive integers (in bytes)">;

def warn_drv_msp430_hwmult_unsupported : Warning<
"the given MCU does not support hardware multiply, but '-mhwmult' is set to "
"%0">, InGroup<InvalidCommandLineArgument>;
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2 changes: 2 additions & 0 deletions clang/include/clang/Basic/LangOptions.def
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Expand Up @@ -378,6 +378,8 @@ ENUM_LANGOPT(TrivialAutoVarInit, TrivialAutoVarInitKind, 2, TrivialAutoVarInitKi
"trivial automatic variable initialization")
VALUE_LANGOPT(TrivialAutoVarInitStopAfter, 32, 0,
"stop trivial automatic variable initialization after the specified number of instances. Must be greater than 0.")
VALUE_LANGOPT(TrivialAutoVarInitMaxSize, 32, 0,
"stop trivial automatic variable initialization if var size exceeds the specified size (in bytes). Must be greater than 0.")
ENUM_LANGOPT(SignedOverflowBehavior, SignedOverflowBehaviorTy, 2, SOB_Undefined,
"signed integer overflow handling")
ENUM_LANGOPT(ThreadModel , ThreadModelKind, 2, ThreadModelKind::POSIX, "Thread Model")
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4 changes: 4 additions & 0 deletions clang/include/clang/Driver/Options.td
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Expand Up @@ -3664,6 +3664,10 @@ def ftrivial_auto_var_init_stop_after : Joined<["-"], "ftrivial-auto-var-init-st
Visibility<[ClangOption, CC1Option, CLOption, DXCOption]>,
HelpText<"Stop initializing trivial automatic stack variables after the specified number of instances">,
MarshallingInfoInt<LangOpts<"TrivialAutoVarInitStopAfter">>;
def ftrivial_auto_var_init_max_size : Joined<["-"], "ftrivial-auto-var-init-max-size=">, Group<f_Group>,
Visibility<[ClangOption, CC1Option, CLOption, DXCOption]>,
HelpText<"Stop initializing trivial automatic stack variables if var size exceeds the specified number of instances (in bytes)">,
MarshallingInfoInt<LangOpts<"TrivialAutoVarInitMaxSize">>;
def fstandalone_debug : Flag<["-"], "fstandalone-debug">, Group<f_Group>,
Visibility<[ClangOption, CLOption, DXCOption]>,
HelpText<"Emit full debug info for all types used by the program">;
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14 changes: 14 additions & 0 deletions clang/lib/CodeGen/CGDecl.cpp
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Expand Up @@ -1759,20 +1759,34 @@ void CodeGenFunction::emitZeroOrPatternForAutoVarInit(QualType type,
const VarDecl &D,
Address Loc) {
auto trivialAutoVarInit = getContext().getLangOpts().getTrivialAutoVarInit();
auto trivialAutoVarInitMaxSize =
getContext().getLangOpts().TrivialAutoVarInitMaxSize;
CharUnits Size = getContext().getTypeSizeInChars(type);
bool isVolatile = type.isVolatileQualified();
if (!Size.isZero()) {
// We skip auto-init variables by their alloc size. Take this as an example:
// "struct Foo {int x; char buff[1024];}" Assume the max-size flag is 1023.
// All Foo type variables will be skipped. Ideally, we only skip the buff
// array and still auto-init X in this example.
// TODO: Improve the size filtering to by member size.
auto allocSize = CGM.getDataLayout().getTypeAllocSize(Loc.getElementType());
switch (trivialAutoVarInit) {
case LangOptions::TrivialAutoVarInitKind::Uninitialized:
llvm_unreachable("Uninitialized handled by caller");
case LangOptions::TrivialAutoVarInitKind::Zero:
if (CGM.stopAutoInit())
return;
if (trivialAutoVarInitMaxSize > 0 &&
allocSize > trivialAutoVarInitMaxSize)
return;
emitStoresForZeroInit(CGM, D, Loc, isVolatile, Builder);
break;
case LangOptions::TrivialAutoVarInitKind::Pattern:
if (CGM.stopAutoInit())
return;
if (trivialAutoVarInitMaxSize > 0 &&
allocSize > trivialAutoVarInitMaxSize)
return;
emitStoresForPatternInit(CGM, D, Loc, isVolatile, Builder);
break;
}
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14 changes: 14 additions & 0 deletions clang/lib/Driver/ToolChains/Clang.cpp
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Expand Up @@ -3535,6 +3535,20 @@ static void RenderTrivialAutoVarInitOptions(const Driver &D,
CmdArgs.push_back(
Args.MakeArgString("-ftrivial-auto-var-init-stop-after=" + Val));
}

if (Arg *A = Args.getLastArg(options::OPT_ftrivial_auto_var_init_max_size)) {
if (!Args.hasArg(options::OPT_ftrivial_auto_var_init) ||
StringRef(
Args.getLastArg(options::OPT_ftrivial_auto_var_init)->getValue()) ==
"uninitialized")
D.Diag(diag::err_drv_trivial_auto_var_init_max_size_missing_dependency);
A->claim();
StringRef Val = A->getValue();
if (std::stoi(Val.str()) <= 0)
D.Diag(diag::err_drv_trivial_auto_var_init_max_size_invalid_value);
CmdArgs.push_back(
Args.MakeArgString("-ftrivial-auto-var-init-max-size=" + Val));
}
}

static void RenderOpenCLOptions(const ArgList &Args, ArgStringList &CmdArgs,
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83 changes: 83 additions & 0 deletions clang/test/CodeGenCXX/auto-var-init-max-size.cpp
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@@ -0,0 +1,83 @@
// Pattern related max size tests: 1, 1024, 4096
// RUN: %clang_cc1 -triple x86_64-unknown-unknown -ftrivial-auto-var-init=pattern -ftrivial-auto-var-init-max-size=1 %s -emit-llvm -o - | FileCheck -check-prefix=PATTERN-COMMON -check-prefix=PATTERN-MAX-1 %s
// RUN: %clang_cc1 -triple x86_64-unknown-unknown -ftrivial-auto-var-init=pattern -ftrivial-auto-var-init-max-size=1024 %s -emit-llvm -o - | FileCheck -check-prefix=PATTERN-COMMON -check-prefix=PATTERN-MAX-1024 %s
// RUN: %clang_cc1 -triple x86_64-unknown-unknown -ftrivial-auto-var-init=pattern -ftrivial-auto-var-init-max-size=4096 %s -emit-llvm -o - | FileCheck -check-prefix=PATTERN-COMMON -check-prefix=PATTERN-MAX-4096 %s
//
// Zero related max size tests: 1, 1024, 4096
// RUN: %clang_cc1 -triple x86_64-unknown-unknown -ftrivial-auto-var-init=zero -ftrivial-auto-var-init-max-size=1 %s -emit-llvm -o - | FileCheck -check-prefix=ZERO-COMMON -check-prefix=ZERO-MAX-1 %s
// RUN: %clang_cc1 -triple x86_64-unknown-unknown -ftrivial-auto-var-init=zero -ftrivial-auto-var-init-max-size=1024 %s -emit-llvm -o - | FileCheck -check-prefix=ZERO-COMMON -check-prefix=ZERO-MAX-1024 %s
// RUN: %clang_cc1 -triple x86_64-unknown-unknown -ftrivial-auto-var-init=zero -ftrivial-auto-var-init-max-size=4096 %s -emit-llvm -o - | FileCheck -check-prefix=ZERO-COMMON -check-prefix=ZERO-MAX-4096 %s

struct Foo {
int x; // we should try to make sure X is initialized.
char buff[1024]; // this one is fine to skip
};

int foo(unsigned n) {
bool var_size_1;
long var_size_8 = 123;
void *var_size_8p;
int var_size_1024[256];
Foo var_size_1028;
int var_size_4096[1024];
// VLA, non-constant size
int var_vla[n];
// builtin, non-constant size
var_size_8p = __builtin_alloca(sizeof(unsigned long long) * n);
// There are 8 variables: var_size_1, var_size_8, var_size_8p, var_size_1024,
// var_size_1028, var_size_4096, var_vla, and a builtin anonymous var ("%5").
// - COMMON (auto-init regardless of the max size): "var_vla", and "%5"
// - Max size 1: "var_size_1"
// - Max size 1024: "var_size_1", "var_size_8", "var_size_8p", "var_size_1024"
// - Max size 4096: "var_size_1", "var_size_8", "var_size_8p", "var_size_1024", "var_size_1028", "var_size_4096"
//
// PATTERN-MAX-1: store i8 -86, ptr %var_size_1, align 1, !annotation [[AUTO_INIT:!.+]]
// PATTERN-MAX-1-NOT: store i64 -6148914691236517206, ptr %var_size_8, align 8, !annotation [[AUTO_INIT:!.+]]
// PATTERN-MAX-1-NOT: store ptr inttoptr (i64 -6148914691236517206 to ptr), ptr %var_size_8p, align 8, !annotation [[AUTO_INIT:!.+]]
// PATTERN-MAX-1-NOT: call void @llvm.memset.p0.i64(ptr align 16 %var_size_1024, i8 -86, i64 1024, i1 false), !annotation [[AUTO_INIT:!.+]]
// PATTERN-MAX-1-NOT: call void @llvm.memset.p0.i64(ptr align 4 %var_size_1028, i8 -86, i64 1028, i1 false), !annotation [[AUTO_INIT:!.+]]
// PATTERN-MAX-1-NOT: call void @llvm.memset.p0.i64(ptr align 16 %var_size_4096, i8 -86, i64 4096, i1 false), !annotation [[AUTO_INIT:!.+]]

// PATTERN-MAX-1024: store i8 -86, ptr %var_size_1, align 1, !annotation [[AUTO_INIT:!.+]]
// PATTERN-MAX-1024: store i64 -6148914691236517206, ptr %var_size_8, align 8, !annotation [[AUTO_INIT:!.+]]
// PATTERN-MAX-1024: store ptr inttoptr (i64 -6148914691236517206 to ptr), ptr %var_size_8p, align 8, !annotation [[AUTO_INIT:!.+]]
// PATTERN-MAX-1024: call void @llvm.memset.p0.i64(ptr align 16 %var_size_1024, i8 -86, i64 1024, i1 false), !annotation [[AUTO_INIT:!.+]]
// PATTERN-MAX-1024-NOT: call void @llvm.memset.p0.i64(ptr align 4 %var_size_1028, i8 -86, i64 1028, i1 false), !annotation [[AUTO_INIT:!.+]]
// PATTERN-MAX-1024-NOT: call void @llvm.memset.p0.i64(ptr align 16 %var_size_4096, i8 -86, i64 4096, i1 false), !annotation [[AUTO_INIT:!.+]]

// PATTERN-MAX-4096: store i8 -86, ptr %var_size_1, align 1, !annotation [[AUTO_INIT:!.+]]
// PATTERN-MAX-4096: store i64 -6148914691236517206, ptr %var_size_8, align 8, !annotation [[AUTO_INIT:!.+]]
// PATTERN-MAX-4096: store ptr inttoptr (i64 -6148914691236517206 to ptr), ptr %var_size_8p, align 8, !annotation [[AUTO_INIT:!.+]]
// PATTERN-MAX-4096: call void @llvm.memset.p0.i64(ptr align 16 %var_size_1024, i8 -86, i64 1024, i1 false), !annotation [[AUTO_INIT:!.+]]
// PATTERN-MAX-4096: call void @llvm.memset.p0.i64(ptr align 4 %var_size_1028, i8 -86, i64 1028, i1 false), !annotation [[AUTO_INIT:!.+]]
// PATTERN-MAX-4096: call void @llvm.memset.p0.i64(ptr align 16 %var_size_4096, i8 -86, i64 4096, i1 false), !annotation [[AUTO_INIT:!.+]]

// PATTERN-COMMON: call void @llvm.memcpy.p0.p0.i64(ptr align 4 %vla.cur, ptr align 4 @__const._Z3fooj.var_vla, i64 4, i1 false), !annotation [[AUTO_INIT:!.+]]
// PATTERN-COMMON: call void @llvm.memset.p0.i64(ptr align 16 %5, i8 -86, i64 %mul, i1 false), !annotation [[AUTO_INIT:!.+]]

// ZERO-MAX-1: store i8 0, ptr %var_size_1, align 1, !annotation [[AUTO_INIT:!.+]]
// ZERO-MAX-1-NOT: store i64 0, ptr %var_size_8, align 8, !annotation [[AUTO_INIT:!.+]]
// ZERO-MAX-1-NOT: store ptr null, ptr %var_size_8p, align 8, !annotation [[AUTO_INIT:!.+]]
// ZERO-MAX-1-NOT: call void @llvm.memset.p0.i64(ptr align 16 %var_size_1024, i8 0, i64 1024, i1 false), !annotation [[AUTO_INIT:!.+]]
// ZERO-MAX-1-NOT: call void @llvm.memset.p0.i64(ptr align 4 %var_size_1028, i8 0, i64 1028, i1 false), !annotation [[AUTO_INIT:!.+]]
// ZERO-MAX-1-NOT: call void @llvm.memset.p0.i64(ptr align 16 %var_size_4096, i8 0, i64 4096, i1 false), !annotation [[AUTO_INIT:!.+]]

// ZERO-MAX-1024: store i8 0, ptr %var_size_1, align 1, !annotation [[AUTO_INIT:!.+]]
// ZERO-MAX-1024: store i64 0, ptr %var_size_8, align 8, !annotation [[AUTO_INIT:!.+]]
// ZERO-MAX-1024: store ptr null, ptr %var_size_8p, align 8, !annotation [[AUTO_INIT:!.+]]
// ZERO-MAX-1024: call void @llvm.memset.p0.i64(ptr align 16 %var_size_1024, i8 0, i64 1024, i1 false), !annotation [[AUTO_INIT:!.+]]
// ZERO-MAX-1024-NOT: call void @llvm.memset.p0.i64(ptr align 4 %var_size_1028, i8 0, i64 1028, i1 false), !annotation [[AUTO_INIT:!.+]]
// ZERO-MAX-1024-NOT: call void @llvm.memset.p0.i64(ptr align 16 %var_size_4096, i8 0, i64 4096, i1 false), !annotation [[AUTO_INIT:!.+]]

// ZERO-MAX-4096: store i8 0, ptr %var_size_1, align 1, !annotation [[AUTO_INIT:!.+]]
// ZERO-MAX-4096: store i64 0, ptr %var_size_8, align 8, !annotation [[AUTO_INIT:!.+]]
// ZERO-MAX-4096: store ptr null, ptr %var_size_8p, align 8, !annotation [[AUTO_INIT:!.+]]
// ZERO-MAX-4096: call void @llvm.memset.p0.i64(ptr align 16 %var_size_1024, i8 0, i64 1024, i1 false), !annotation [[AUTO_INIT:!.+]]
// ZERO-MAX-4096: call void @llvm.memset.p0.i64(ptr align 4 %var_size_1028, i8 0, i64 1028, i1 false), !annotation [[AUTO_INIT:!.+]]
// ZERO-MAX-4096: call void @llvm.memset.p0.i64(ptr align 16 %var_size_4096, i8 0, i64 4096, i1 false), !annotation [[AUTO_INIT:!.+]]

// ZERO-COMMON: call void @llvm.memset.p0.i64(ptr align 16 %vla, i8 0, i64 %3, i1 false), !annotation [[AUTO_INIT:!.+]]
// ZERO-COMMON: call void @llvm.memset.p0.i64(ptr align 16 %5, i8 0, i64 %mul, i1 false), !annotation [[AUTO_INIT:!.+]]

return 0;
}
13 changes: 13 additions & 0 deletions clang/test/Driver/clang_f_opts.c
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Expand Up @@ -585,6 +585,19 @@
// CHECK-TRIVIAL-PATTERN-STOP-AFTER-INVALID-VALUE: only accepts positive integers
// CHECK-TRIVIAL-ZERO-STOP-AFTER-INVALID-VALUE: only accepts positive integers

// RUN: %clang -### -S -ftrivial-auto-var-init=pattern -ftrivial-auto-var-init-max-size=1024 %s 2>&1 | FileCheck -check-prefix=CHECK-TRIVIAL-PATTERN-MAX-SIZE %s
// RUN: %clang -### -S -ftrivial-auto-var-init=zero -ftrivial-auto-var-init-max-size=1024 %s 2>&1 | FileCheck -check-prefix=CHECK-TRIVIAL-ZERO-MAX-SIZE %s
// RUN: not %clang -### -S -ftrivial-auto-var-init-max-size=1024 %s 2>&1 | FileCheck -check-prefix=CHECK-TRIVIAL-MAX-SIZE-MISSING-DEPENDENCY %s
// RUN: not %clang -### -S -ftrivial-auto-var-init=pattern -ftrivial-auto-var-init-max-size=0 %s 2>&1 | FileCheck -check-prefix=CHECK-TRIVIAL-PATTERN-MAX-SIZE-INVALID-VALUE %s
// RUN: not %clang -### -S -ftrivial-auto-var-init=zero -ftrivial-auto-var-init-max-size=0 %s 2>&1 | FileCheck -check-prefix=CHECK-TRIVIAL-ZERO-MAX-SIZE-INVALID-VALUE %s
// CHECK-TRIVIAL-PATTERN-MAX-SIZE-NOT: is used without '-ftrivial-auto-var-init'
// CHECK-TRIVIAL-PATTERN-MAX-SIZE-NOT: only accepts positive integers (in bytes)
// CHECK-TRIVIAL-ZERO-MAX-SIZE-NOT: is used without '-ftrivial-auto-var-init'
// CHECK-TRIVIAL-ZERO-MAX-SIZE-NOT: only accepts positive integers (in bytes)
// CHECK-TRIVIAL-MAX-SIZE-MISSING-DEPENDENCY: used without '-ftrivial-auto-var-init=zero' or
// CHECK-TRIVIAL-PATTERN-MAX-SIZE-INVALID-VALUE: only accepts positive integers (in bytes)
// CHECK-TRIVIAL-ZERO-MAX-SIZE-INVALID-VALUE: only accepts positive integers (in bytes)

// RUN: %clang -### -S -fno-temp-file %s 2>&1 | FileCheck -check-prefix=CHECK-NO-TEMP-FILE %s
// CHECK-NO-TEMP-FILE: "-fno-temp-file"

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