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[libc] Support 'assert.h' on the GPU
This patch adds the necessary support to provide `assert` functionality through the GPU `libc` implementation. This implementation creates a special-case GPU implementation rather than relying on the common version. This is because the GPU has special considerings for printing. The assertion is printed out in chunks with `write_to_stderr`, however when combined with the GPU execution model this causes 32+ threads to all execute in-lock step. Meaning that we'll get a horribly fragmented message. Furthermore, potentially thousands of threads could hit the assertion at once and try to print even if we had it all in one `printf`. This is solved by having a one-time lock that each thread group / wave / warp will attempt to claim. We only let one thread group pass through while the others simply stop executing. Finally only the first thread in that group will do the printing until we finally abort execution. Reviewed By: sivachandra Differential Revision: https://reviews.llvm.org/D159296
1 parent 4294bca commit 533145c

12 files changed

Lines changed: 149 additions & 21 deletions

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‎libc/config/gpu/api.td‎

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@@ -3,6 +3,38 @@ include "config/public_api.td"
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include "spec/stdc.td"
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include "spec/posix.td"
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include "spec/gpu_ext.td"
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include "spec/gnu_ext.td"
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include "spec/llvm_libc_ext.td"
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def AssertMacro : MacroDef<"assert"> {
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let Defn = [{
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#undef assert
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#ifdef NDEBUG
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#define assert(e) (void)0
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#else
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#define assert(e) \
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((e) ? (void)0 : __assert_fail(#e, __FILE__, __LINE__, __PRETTY_FUNCTION__))
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#endif
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}];
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}
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def StaticAssertMacro : MacroDef<"static_assert"> {
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let Defn = [{
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#ifndef __cplusplus
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#undef static_assert
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#define static_assert _Static_assert
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#endif
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}];
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}
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def AssertAPI : PublicAPI<"assert.h"> {
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let Macros = [
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AssertMacro,
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StaticAssertMacro,
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];
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}
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def StringAPI : PublicAPI<"string.h"> {
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let Types = ["size_t"];

‎libc/config/gpu/entrypoints.txt‎

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@@ -1,4 +1,7 @@
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set(TARGET_LIBC_ENTRYPOINTS
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# assert.h entrypoints
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libc.src.assert.__assert_fail
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# ctype.h entrypoints
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libc.src.ctype.isalnum
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libc.src.ctype.isalpha

‎libc/config/gpu/headers.txt‎

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@@ -1,4 +1,5 @@
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set(TARGET_PUBLIC_HEADERS
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libc.include.assert
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libc.include.ctype
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libc.include.string
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libc.include.inttypes

‎libc/docs/gpu/support.rst‎

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@@ -130,7 +130,7 @@ fopen |check| |check|
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fread |check| |check|
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============= ========= ============
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stdio.h
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time.h
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--------
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============= ========= ============
@@ -139,3 +139,13 @@ Function Name Available RPC Required
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clock |check|
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nanosleep |check|
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============= ========= ============
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assert.h
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--------
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============= ========= ============
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Function Name Available RPC Required
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============= ========= ============
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assert |check| |check|
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__assert_fail |check| |check|
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============= ========= ============

‎libc/src/__support/GPU/utils.h‎

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@@ -19,4 +19,19 @@
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#include "generic/utils.h"
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#endif
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namespace __llvm_libc {
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namespace gpu {
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/// Get the first active thread inside the lane.
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LIBC_INLINE uint64_t get_first_lane_id(uint64_t lane_mask) {
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return __builtin_ffsl(lane_mask) - 1;
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}
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/// Conditional that is only true for a single thread in a lane.
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LIBC_INLINE bool is_first_lane(uint64_t lane_mask) {
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return gpu::get_lane_id() == get_first_lane_id(lane_mask);
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}
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} // namespace gpu
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} // namespace __llvm_libc
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#endif // LLVM_LIBC_SRC_SUPPORT_OSUTIL_IO_H

‎libc/src/__support/RPC/rpc.h‎

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@@ -214,7 +214,7 @@ template <bool Invert, typename Packet> struct Process {
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// restrict to a single thread to avoid one thread dropping the lock, then
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// an unrelated warp claiming the lock, then a second thread in this warp
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// dropping the lock again.
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clear_nth(lock, index, rpc::is_first_lane(lane_mask));
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clear_nth(lock, index, gpu::is_first_lane(lane_mask));
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gpu::sync_lane(lane_mask);
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}
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@@ -546,7 +546,7 @@ template <uint16_t opcode> LIBC_INLINE Client::Port Client::open() {
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continue;
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}
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if (is_first_lane(lane_mask)) {
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if (gpu::is_first_lane(lane_mask)) {
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process.packet[index].header.opcode = opcode;
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process.packet[index].header.mask = lane_mask;
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}

‎libc/src/__support/RPC/rpc_util.h‎

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@@ -30,16 +30,6 @@ LIBC_INLINE void sleep_briefly() {
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#endif
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}
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/// Get the first active thread inside the lane.
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LIBC_INLINE uint64_t get_first_lane_id(uint64_t lane_mask) {
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return __builtin_ffsl(lane_mask) - 1;
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}
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/// Conditional that is only true for a single thread in a lane.
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LIBC_INLINE bool is_first_lane(uint64_t lane_mask) {
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return gpu::get_lane_id() == get_first_lane_id(lane_mask);
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}
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/// Conditional to indicate if this process is running on the GPU.
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LIBC_INLINE constexpr bool is_process_gpu() {
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#if defined(LIBC_TARGET_ARCH_IS_GPU)

‎libc/src/assert/CMakeLists.txt‎

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@@ -1,12 +1,18 @@
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if(EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/${LIBC_TARGET_OS})
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add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/${LIBC_TARGET_OS})
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else()
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add_subdirectory(generic)
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endif()
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if(TARGET libc.src.assert.${LIBC_TARGET_OS}.__assert_fail)
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set(assert_fail_dep libc.src.assert.${LIBC_TARGET_OS}.__assert_fail)
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else()
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set(assert_fail_dep libc.src.assert.generic.__assert_fail)
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endif()
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add_entrypoint_object(
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__assert_fail
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SRCS
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__assert_fail.cpp
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HDRS
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__assert_fail.h
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assert.h
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ALIAS
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DEPENDS
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libc.include.assert
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libc.src.__support.OSUtil.osutil
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libc.src.stdlib.abort
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${assert_fail_dep}
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)

‎libc/src/assert/generic/CMakeLists.txt‎

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@@ -0,0 +1,12 @@
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add_entrypoint_object(
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__assert_fail
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SRCS
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__assert_fail.cpp
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HDRS
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../__assert_fail.h
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../assert.h
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DEPENDS
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libc.include.assert
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libc.src.__support.OSUtil.osutil
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libc.src.stdlib.abort
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)

libc/src/assert/__assert_fail.cpp renamed to libc/src/assert/generic/__assert_fail.cpp

File renamed without changes.

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