From ebaaf85a35b6e2bd59bc6bfbefb66e7595c751d1 Mon Sep 17 00:00:00 2001
From: Vedant Kumar <vsk@apple.com>
Date: Mon, 17 Apr 2017 22:26:10 +0000
Subject: [PATCH] [ubsan] Skip null checks if they are constant-folded away
The IR builder can constant-fold null checks if the pointer operand
points to a constant. If the "is-non-null" check is folded away to
"true", don't emit the null check + branch.
Testing: check-clang, check-ubsan.
This slightly reduces the amount of null checks we emit when compiling
X86ISelLowering.cpp. Here are the numbers from patched/unpatched clangs
based on r300371.
-------------------------------------
| Setup | # of null checks |
-------------------------------------
| unpatched, -O0 | 25251 |
| patched, -O0 | 23925 | (-5.3%)
-------------------------------------
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@300509 91177308-0d34-0410-b5e6-96231b3b80d8
---
lib/CodeGen/CGExpr.cpp | 26 +++++++++++++++--------
test/CodeGenCXX/ubsan-suppress-checks.cpp | 2 ++
2 files changed, 19 insertions(+), 9 deletions(-)
diff --git a/lib/CodeGen/CGExpr.cpp b/lib/CodeGen/CGExpr.cpp
index b5d6c659e9e..719147a58e0 100644
--- a/lib/CodeGen/CGExpr.cpp
+++ b/lib/CodeGen/CGExpr.cpp
@@ -568,15 +568,23 @@ void CodeGenFunction::EmitTypeCheck(TypeCheckKind TCK, SourceLocation Loc,
// The glvalue must not be an empty glvalue.
llvm::Value *IsNonNull = Builder.CreateIsNotNull(Ptr);
- if (AllowNullPointers) {
- // When performing pointer casts, it's OK if the value is null.
- // Skip the remaining checks in that case.
- Done = createBasicBlock("null");
- llvm::BasicBlock *Rest = createBasicBlock("not.null");
- Builder.CreateCondBr(IsNonNull, Rest, Done);
- EmitBlock(Rest);
- } else {
- Checks.push_back(std::make_pair(IsNonNull, SanitizerKind::Null));
+ // The IR builder can constant-fold the null check if the pointer points to
+ // a constant.
+ bool PtrIsNonNull =
+ IsNonNull == llvm::ConstantInt::getTrue(getLLVMContext());
+
+ // Skip the null check if the pointer is known to be non-null.
+ if (!PtrIsNonNull) {
+ if (AllowNullPointers) {
+ // When performing pointer casts, it's OK if the value is null.
+ // Skip the remaining checks in that case.
+ Done = createBasicBlock("null");
+ llvm::BasicBlock *Rest = createBasicBlock("not.null");
+ Builder.CreateCondBr(IsNonNull, Rest, Done);
+ EmitBlock(Rest);
+ } else {
+ Checks.push_back(std::make_pair(IsNonNull, SanitizerKind::Null));
+ }
}
}
diff --git a/test/CodeGenCXX/ubsan-suppress-checks.cpp b/test/CodeGenCXX/ubsan-suppress-checks.cpp
index a8ca24ba63a..d0e7b32ef96 100644
--- a/test/CodeGenCXX/ubsan-suppress-checks.cpp
+++ b/test/CodeGenCXX/ubsan-suppress-checks.cpp
@@ -10,6 +10,8 @@ void load_non_null_pointers() {
int arr[1];
arr[0] = arr[0];
+ char c = "foo"[0];
+
// CHECK-NOT: icmp ne {{.*}}, null, !nosanitize
// CHECK: ret void
}
--
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