[FFmpeg-devel] [PATCH v4 2/4] libavutils: Add parse_r helper for MIPS

[Shiyou Yin]

>-----Original Message-----
>From: ffmpeg-devel-bounces at ffmpeg.org [mailto:ffmpeg-devel-bounces at ffmpeg.org] On Behalf Of
>Jiaxun Yang
>Sent: Monday, June 8, 2020 11:30 AM
>To: ffmpeg-devel at ffmpeg.org
>Cc: yinshiyou at loongson.cn; Jiaxun Yang
>Subject: [FFmpeg-devel] [PATCH v4 2/4] libavutils: Add parse_r helper for MIPS
>
>That helper grab from kernel code can allow us to inline
>newer instructions (not implemented by the assembler) in
>a elegant manner.
>
>Signed-off-by: Jiaxun Yang <jiaxun.yang at flygoat.com>
>---
> libavutil/mips/asmdefs.h | 42 ++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 42 insertions(+)
>
>diff --git a/libavutil/mips/asmdefs.h b/libavutil/mips/asmdefs.h
>index 748119918a..7e0e4cf575 100644
>--- a/libavutil/mips/asmdefs.h
>+++ b/libavutil/mips/asmdefs.h
>@@ -55,4 +55,46 @@
> # define PTR_SLL        "sll "
> #endif
>
>+/*
>+ * parse_r var, r - Helper assembler macro for parsing register names.
>+ *
>+ * This converts the register name in $n form provided in \r to the
>+ * corresponding register number, which is assigned to the variable \var. It is
>+ * needed to allow explicit encoding of instructions in inline assembly where
>+ * registers are chosen by the compiler in $n form, allowing us to avoid using
>+ * fixed register numbers.
>+ *
>+ * It also allows newer instructions (not implemented by the assembler) to be
>+ * transparently implemented using assembler macros, instead of needing separate
>+ * cases depending on toolchain support.
>+ *
>+ * Simple usage example:
>+ * __asm__ __volatile__("parse_r __rt, %0\n\t"
>+ *			".insn\n\t"
>+ *			"# di    %0\n\t"
>+ *			".word   (0x41606000 | (__rt << 16))"
>+ *			: "=r" (status);
>+ */
>+
>+/* Match an individual register number and assign to \var */
>+#define _IFC_REG(n)				\
>+	".ifc	\\r, $" #n "\n\t"		\
>+	"\\var	= " #n "\n\t"			\
>+	".endif\n\t"
>+
>+__asm__(".macro	parse_r var r\n\t"
>+	"\\var	= -1\n\t"
>+	_IFC_REG(0)  _IFC_REG(1)  _IFC_REG(2)  _IFC_REG(3)
>+	_IFC_REG(4)  _IFC_REG(5)  _IFC_REG(6)  _IFC_REG(7)
>+	_IFC_REG(8)  _IFC_REG(9)  _IFC_REG(10) _IFC_REG(11)
>+	_IFC_REG(12) _IFC_REG(13) _IFC_REG(14) _IFC_REG(15)
>+	_IFC_REG(16) _IFC_REG(17) _IFC_REG(18) _IFC_REG(19)
>+	_IFC_REG(20) _IFC_REG(21) _IFC_REG(22) _IFC_REG(23)
>+	_IFC_REG(24) _IFC_REG(25) _IFC_REG(26) _IFC_REG(27)
>+	_IFC_REG(28) _IFC_REG(29) _IFC_REG(30) _IFC_REG(31)
>+	".iflt	\\var\n\t"
>+	".error	\"Unable to parse register name \\r\"\n\t"
>+	".endif\n\t"
>+	".endm");
>+

In inline assembler, we can add asmSymbolicName in Input/ Output Operands, format:
[ [asmSymbolicName] ] constraint (cExpression)
[ [asmSymbolicName] ] constraint (cVariableName)

> #endif /* AVCODEC_MIPS_ASMDEFS_H */
>--
>2.20.1
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