9e0c06d708
Let Clang emit `dead_on_return` attribute on pointer arguments that are passed indirectly, namely, large aggregates that the ABI mandates be passed by value; thus, the parameter is destroyed within the callee. Writes to such arguments are not observable by the caller after the callee returns. This should desirably enable further MemCpyOpt/DSE optimizations. Previous discussion: https://discourse.llvm.org/t/rfc-add-dead-on-return-attribute/86871.
40 lines
1.2 KiB
C
40 lines
1.2 KiB
C
// RUN: %clang_cc1 -O3 -triple aarch64 -target-feature +sve -mvscale-min=1 -mvscale-max=1 -emit-llvm -o - %s | FileCheck %s --check-prefixes=CHECK-C
|
|
// RUN: %clang_cc1 -x c++ -O3 -triple aarch64 -target-feature +sve -mvscale-min=1 -mvscale-max=1 -emit-llvm -o - %s | FileCheck %s --check-prefixes=CHECK-CXX
|
|
|
|
typedef __SVFloat32_t fvec32 __attribute__((arm_sve_vector_bits(128)));
|
|
|
|
// PST containing an empty union: when compiled as C pass it in registers,
|
|
// when compiled as C++ - in memory.
|
|
typedef struct {
|
|
fvec32 x[4];
|
|
union {} u;
|
|
} S0;
|
|
|
|
#ifdef __cplusplus
|
|
extern "C"
|
|
#endif
|
|
void use0(S0);
|
|
|
|
void f0(S0 *p) {
|
|
use0(*p);
|
|
}
|
|
// CHECK-C: declare void @use0(<vscale x 4 x float>, <vscale x 4 x float>, <vscale x 4 x float>, <vscale x 4 x float>)
|
|
// CHECK-CXX: declare void @use0(ptr dead_on_return noundef)
|
|
|
|
#ifdef __cplusplus
|
|
|
|
// PST containing an empty union with `[[no_unique_address]]`` - pass in registers.
|
|
typedef struct {
|
|
fvec32 x[4];
|
|
[[no_unique_address]]
|
|
union {} u;
|
|
} S1;
|
|
|
|
extern "C" void use1(S1);
|
|
void f1(S1 *p) {
|
|
use1(*p);
|
|
}
|
|
// CHECK-CXX: declare void @use1(<vscale x 4 x float>, <vscale x 4 x float>, <vscale x 4 x float>, <vscale x 4 x float>)
|
|
|
|
#endif // __cplusplus
|