Author: vedantk
Date: Tue Apr 25 21:17:21 2017
New Revision: 301377
URL: http://llvm.org/viewvc/llvm-project?rev=301377&view=rev
Log:
[ubsan] Skip alignment checks on allocas with known alignment
It's possible to determine the alignment of an alloca at compile-time.
Use this information to skip emitting some runtime alignment checks.
Testing: check-clang, check-ubsan.
This significantly reduces the amount of alignment checks we emit when
compiling X86ISelLowering.cpp. Here are the numbers from patched/unpatched
clangs based on r301361.
------------------------------------------
| Setup | # of alignment checks |
------------------------------------------
| unpatched, -O0 | 47195 |
| patched, -O0 | 30876 | (-34.6%)
------------------------------------------
Modified:
cfe/trunk/lib/CodeGen/CGExpr.cpp
cfe/trunk/test/CodeGen/catch-undef-behavior.c
cfe/trunk/test/CodeGen/sanitize-recover.c
cfe/trunk/test/CodeGenCXX/ubsan-suppress-checks.cpp
Modified: cfe/trunk/lib/CodeGen/CGExpr.cpp
URL:
http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/CodeGen/CGExpr.cpp?rev=301377&r1=301376&r2=301377&view=diff
==============================================================================
--- cfe/trunk/lib/CodeGen/CGExpr.cpp (original)
+++ cfe/trunk/lib/CodeGen/CGExpr.cpp Tue Apr 25 21:17:21 2017
@@ -533,15 +533,6 @@ bool CodeGenFunction::sanitizePerformTyp
SanOpts.has(SanitizerKind::Vptr);
}
-/// Check if a runtime null check for \p Ptr can be omitted.
-static bool canOmitPointerNullCheck(llvm::Value *Ptr) {
- // Note: do not perform any constant-folding in this function. That is best
- // left to the IR builder.
-
- // Pointers to alloca'd memory are non-null.
- return isa<llvm::AllocaInst>(Ptr->stripPointerCastsNoFollowAliases());
-}
-
void CodeGenFunction::EmitTypeCheck(TypeCheckKind TCK, SourceLocation Loc,
llvm::Value *Ptr, QualType Ty,
CharUnits Alignment,
@@ -560,11 +551,16 @@ void CodeGenFunction::EmitTypeCheck(Type
SmallVector<std::pair<llvm::Value *, SanitizerMask>, 3> Checks;
llvm::BasicBlock *Done = nullptr;
+ // Quickly determine whether we have a pointer to an alloca. It's possible
+ // to skip null checks, and some alignment checks, for these pointers. This
+ // can reduce compile-time significantly.
+ auto PtrToAlloca =
+ dyn_cast<llvm::AllocaInst>(Ptr->stripPointerCastsNoFollowAliases());
+
bool AllowNullPointers = TCK == TCK_DowncastPointer || TCK == TCK_Upcast ||
TCK == TCK_UpcastToVirtualBase;
if ((SanOpts.has(SanitizerKind::Null) || AllowNullPointers) &&
- !SkippedChecks.has(SanitizerKind::Null) &&
- !canOmitPointerNullCheck(Ptr)) {
+ !SkippedChecks.has(SanitizerKind::Null) && !PtrToAlloca) {
// The glvalue must not be an empty glvalue.
llvm::Value *IsNonNull = Builder.CreateIsNotNull(Ptr);
@@ -617,7 +613,8 @@ void CodeGenFunction::EmitTypeCheck(Type
AlignVal = getContext().getTypeAlignInChars(Ty).getQuantity();
// The glvalue must be suitably aligned.
- if (AlignVal > 1) {
+ if (AlignVal > 1 &&
+ (!PtrToAlloca || PtrToAlloca->getAlignment() < AlignVal)) {
llvm::Value *Align =
Builder.CreateAnd(Builder.CreatePtrToInt(Ptr, IntPtrTy),
llvm::ConstantInt::get(IntPtrTy, AlignVal - 1));
Modified: cfe/trunk/test/CodeGen/catch-undef-behavior.c
URL:
http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CodeGen/catch-undef-behavior.c?rev=301377&r1=301376&r2=301377&view=diff
==============================================================================
--- cfe/trunk/test/CodeGen/catch-undef-behavior.c (original)
+++ cfe/trunk/test/CodeGen/catch-undef-behavior.c Tue Apr 25 21:17:21 2017
@@ -36,13 +36,7 @@ void foo() {
// CHECK-COMMON: %[[I8PTR:.*]] = bitcast i32* %[[PTR:.*]] to i8*
// CHECK-COMMON-NEXT: %[[SIZE:.*]] = call i64 @llvm.objectsize.i64.p0i8(i8*
%[[I8PTR]], i1 false, i1 false)
- // CHECK-COMMON-NEXT: %[[CHECK0:.*]] = icmp uge i64 %[[SIZE]], 4
-
- // CHECK-COMMON: %[[PTRTOINT:.*]] = ptrtoint {{.*}}* %[[PTR]] to i64
- // CHECK-COMMON-NEXT: %[[MISALIGN:.*]] = and i64 %[[PTRTOINT]], 3
- // CHECK-COMMON-NEXT: %[[CHECK1:.*]] = icmp eq i64 %[[MISALIGN]], 0
-
- // CHECK-COMMON: %[[OK:.*]] = and i1 %[[CHECK0]], %[[CHECK1]]
+ // CHECK-COMMON-NEXT: %[[OK:.*]] = icmp uge i64 %[[SIZE]], 4
// CHECK-UBSAN: br i1 %[[OK]], {{.*}} !prof ![[WEIGHT_MD:.*]], !nosanitize
// CHECK-TRAP: br i1 %[[OK]], {{.*}}
Modified: cfe/trunk/test/CodeGen/sanitize-recover.c
URL:
http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CodeGen/sanitize-recover.c?rev=301377&r1=301376&r2=301377&view=diff
==============================================================================
--- cfe/trunk/test/CodeGen/sanitize-recover.c (original)
+++ cfe/trunk/test/CodeGen/sanitize-recover.c Tue Apr 25 21:17:21 2017
@@ -22,15 +22,7 @@ void foo() {
// PARTIAL: %[[SIZE:.*]] = call i64 @llvm.objectsize.i64.p0i8(i8*
{{.*}}, i1 false, i1 false)
// PARTIAL-NEXT: %[[CHECK0:.*]] = icmp uge i64 %[[SIZE]], 4
- // PARTIAL: %[[MISALIGN:.*]] = and i64 {{.*}}, 3
- // PARTIAL-NEXT: %[[CHECK1:.*]] = icmp eq i64 %[[MISALIGN]], 0
+ // PARTIAL: br i1 %[[CHECK0]], {{.*}} !nosanitize
- // PARTIAL: %[[CHECK01:.*]] = and i1 %[[CHECK1]], %[[CHECK0]]
-
- // PARTIAL: br i1 %[[CHECK01]], {{.*}} !nosanitize
- // PARTIAL: br i1 %[[CHECK1]], {{.*}} !nosanitize
-
- // PARTIAL: call void @__ubsan_handle_type_mismatch_v1_abort(
- // PARTIAL-NEXT: unreachable
// PARTIAL: call void @__ubsan_handle_type_mismatch_v1(
}
Modified: cfe/trunk/test/CodeGenCXX/ubsan-suppress-checks.cpp
URL:
http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CodeGenCXX/ubsan-suppress-checks.cpp?rev=301377&r1=301376&r2=301377&view=diff
==============================================================================
--- cfe/trunk/test/CodeGenCXX/ubsan-suppress-checks.cpp (original)
+++ cfe/trunk/test/CodeGenCXX/ubsan-suppress-checks.cpp Tue Apr 25 21:17:21 2017
@@ -12,6 +12,7 @@ void load_non_null_pointers() {
char c = "foo"[0];
+ // CHECK-NOT: and i64 {{.*}}, !nosanitize
// CHECK-NOT: icmp ne {{.*}}, null, !nosanitize
// CHECK: ret void
}
@@ -43,10 +44,6 @@ struct A {
};
f();
- // LAMBDA: %[[LAMBDAINT:[0-9]+]] = ptrtoint %class.anon* %[[FUNCVAR:.*]]
to i64, !nosanitize
- // LAMBDA: and i64 %[[LAMBDAINT]], 7, !nosanitize
- // LAMBDA: call void @__ubsan_handle_type_mismatch
-
// LAMBDA-NOT: call void @__ubsan_handle_type_mismatch
// LAMBDA: ret void
}
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