1 files changed, 65 insertions, 0 deletions
diff --git a/third_party/jpeg-xl/lib/jxl/base/iaca.h b/third_party/jpeg-xl/lib/jxl/base/iaca.h
new file mode 100644
index 0000000000..e5732dae5c
--- /dev/null
+++ b/third_party/jpeg-xl/lib/jxl/base/iaca.h
@@ -0,0 +1,65 @@
+// 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_