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// Copyright (c) the JPEG XL Project Authors. All rights reserved.
//
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
#ifndef LIB_JXL_BASE_IACA_H_
#define LIB_JXL_BASE_IACA_H_
#include "lib/jxl/base/compiler_specific.h"
// IACA (Intel's Code Analyzer) analyzes instruction latencies, but only for
// code between special markers. These functions embed such markers in an
// executable, but only for reading via IACA - they deliberately trigger a
// crash if executed to ensure they are removed in normal builds.
#ifndef JXL_IACA_ENABLED
#define JXL_IACA_ENABLED 0
#endif
namespace jxl {
// Call before the region of interest.
static JXL_INLINE void BeginIACA() {
#if JXL_IACA_ENABLED && (JXL_COMPILER_GCC || JXL_COMPILER_CLANG)
asm volatile(
// UD2 "instruction" raises an invalid opcode exception.
".byte 0x0F, 0x0B\n\t"
// Magic sequence recognized by IACA (MOV + addr32 fs:NOP). This actually
// clobbers EBX, but we don't care because the code won't be run, and we
// want IACA to observe the same code the compiler would have generated
// without this marker.
"movl $111, %%ebx\n\t"
".byte 0x64, 0x67, 0x90\n\t"
:
:
// (Allegedly) clobbering memory may prevent reordering.
: "memory");
#endif
}
// Call after the region of interest.
static JXL_INLINE void EndIACA() {
#if JXL_IACA_ENABLED && (JXL_COMPILER_GCC || JXL_COMPILER_CLANG)
asm volatile(
// See above.
"movl $222, %%ebx\n\t"
".byte 0x64, 0x67, 0x90\n\t"
// UD2
".byte 0x0F, 0x0B\n\t"
:
:
// (Allegedly) clobbering memory may prevent reordering.
: "memory");
#endif
}
// Add to a scope to mark a region.
struct ScopeIACA {
JXL_INLINE ScopeIACA() { BeginIACA(); }
JXL_INLINE ~ScopeIACA() { EndIACA(); }
};
} // namespace jxl
#endif // LIB_JXL_BASE_IACA_H_
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