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[safestack] Layout large allocas first to reduce fragmentation.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@277544 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Evgeniy Stepanov 2016-08-02 23:21:30 +00:00
parent 75834f76b2
commit 66c2ec1bb4
2 changed files with 47 additions and 0 deletions
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8
lib/CodeGen/SafeStackLayout.cpp
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@ -132,6 +132,14 @@ void StackLayout::computeLayout() {
// If this is replaced with something smarter, it must preserve the property // If this is replaced with something smarter, it must preserve the property
// that the first object is always at the offset 0 in the stack frame (for // that the first object is always at the offset 0 in the stack frame (for
// StackProtectorSlot), or handle stack protector in some other way. // StackProtectorSlot), or handle stack protector in some other way.
// Sort objects by size (largest first) to reduce fragmentation.
if (StackObjects.size() > 2)
std::stable_sort(StackObjects.begin() + 1, StackObjects.end(),
[](const StackObject &a, const StackObject &b) {
return a.Size > b.Size;
});
for (auto &Obj : StackObjects) for (auto &Obj : StackObjects)
layoutObject(Obj); layoutObject(Obj);

39
test/Transforms/SafeStack/layout-frag.ll Normal file
View File

@ -0,0 +1,39 @@
; Test that safestack layout reuses a region w/o fragmentation.
; RUN: opt -safe-stack -S -mtriple=x86_64-pc-linux-gnu < %s -o - | FileCheck %s
define void @f() safestack {
; CHECK-LABEL: define void @f
entry:
; CHECK: %[[USP:.*]] = load i8*, i8** @__safestack_unsafe_stack_ptr
; CHECK: getelementptr i8, i8* %[[USP]], i32 -16
%x0 = alloca i64, align 8
%x1 = alloca i8, align 1
%x2 = alloca i64, align 8
%x0a = bitcast i64* %x0 to i8*
%x2a = bitcast i64* %x2 to i8*
call void @llvm.lifetime.start(i64 4, i8* %x0a)
call void @capture64(i64* %x0)
call void @llvm.lifetime.end(i64 4, i8* %x0a)
call void @llvm.lifetime.start(i64 4, i8* %x1)
call void @llvm.lifetime.start(i64 4, i8* %x2a)
call void @capture8(i8* %x1)
call void @capture64(i64* %x2)
call void @llvm.lifetime.end(i64 4, i8* %x1)
call void @llvm.lifetime.end(i64 4, i8* %x2a)
; Test that i64 allocas share space.
; CHECK: getelementptr i8, i8* %unsafe_stack_ptr, i32 -8
; CHECK: getelementptr i8, i8* %unsafe_stack_ptr, i32 -9
; CHECK: getelementptr i8, i8* %unsafe_stack_ptr, i32 -8
ret void
}
declare void @llvm.lifetime.start(i64, i8* nocapture)
declare void @llvm.lifetime.end(i64, i8* nocapture)
declare void @capture8(i8*)
declare void @capture64(i64*)