158d72d728
Set the writable and dead_on_unwind attributes for sret arguments. These indicate that the argument points to writable memory (and it's legal to introduce spurious writes to it on entry to the function) and that the argument memory will not be used if the call unwinds. This enables additional MemCpyOpt/DSE/LICM optimizations.
52 lines
1.6 KiB
C++
52 lines
1.6 KiB
C++
// RUN: %clang_cc1 -triple armv7l-unknown-linux-gnueabihf -emit-llvm -O1 -disable-llvm-passes -std=c++03 %s -o - | FileCheck %s --implicit-check-not=llvm.lifetime
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class S {
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char *ptr;
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unsigned int len;
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};
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class T {
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S left;
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S right;
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public:
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T(const char s[]);
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T(S);
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T concat(const T &Suffix) const;
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const char * str() const;
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};
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const char * f(S s)
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{
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// It's essential that the lifetimes of all three T temporaries here are
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// overlapping. They must all remain alive through the call to str().
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//
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// CHECK: [[T1:%.*]] = alloca %class.T, align 4
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// CHECK: [[T2:%.*]] = alloca %class.T, align 4
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// CHECK: [[T3:%.*]] = alloca %class.T, align 4
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//
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// FIXME: We could defer starting the lifetime of the return object of concat
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// until the call.
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// CHECK: call void @llvm.lifetime.start.p0(i64 16, ptr [[T1]])
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//
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// CHECK: call void @llvm.lifetime.start.p0(i64 16, ptr [[T2]])
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// CHECK: [[T4:%.*]] = call noundef ptr @_ZN1TC1EPKc(ptr {{[^,]*}} [[T2]], ptr noundef @.str)
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//
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// CHECK: call void @llvm.lifetime.start.p0(i64 16, ptr [[T3]])
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// CHECK: [[T5:%.*]] = call noundef ptr @_ZN1TC1E1S(ptr {{[^,]*}} [[T3]], [2 x i32] %{{.*}})
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//
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// CHECK: call void @_ZNK1T6concatERKS_(ptr dead_on_unwind writable sret(%class.T) align 4 [[T1]], ptr {{[^,]*}} [[T2]], ptr noundef nonnull align 4 dereferenceable(16) [[T3]])
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// CHECK: [[T6:%.*]] = call noundef ptr @_ZNK1T3strEv(ptr {{[^,]*}} [[T1]])
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//
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// CHECK: call void @llvm.lifetime.end.p0(
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// CHECK: call void @llvm.lifetime.end.p0(
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// CHECK: call void @llvm.lifetime.end.p0(
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// CHECK: ret ptr [[T6]]
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return T("[").concat(T(s)).str();
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}
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// CHECK: declare {{.*}}llvm.lifetime.start
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// CHECK: declare {{.*}}llvm.lifetime.end
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