These options are defined for the PDP-11:
-mfpuUse hardware FPP floating point. This is the default. (FIS floating point on the PDP-11/40 is not supported.) Implies -m45.
-msoft-floatDo not use hardware floating point.
-mac0Return floating-point results in ac0 (fr0 in Unix assembler syntax).
-mno-ac0Return floating-point results in memory. This is the default.
-m40Generate code for a PDP-11/40. Implies -msoft-float -mno-split.
-m45Generate code for a PDP-11/45. This is the default.
-m10Generate code for a PDP-11/10. Implies -msoft-float -mno-split.
-mint16-mno-int32Use 16-bit int. This is the default.
-mint32-mno-int16Use 32-bit int.
-msplitTarget has split instruction and data space. Implies -m45.
-munix-asmUse Unix assembler syntax.
-mdec-asmUse DEC assembler syntax.
-mgnu-asmUse GNU assembler syntax. This is the default.
-mlraUse the new LRA register allocator. By default, the old “reload” allocator is used.
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Licensed under the GNU Free Documentation License, Version 1.3.
https://gcc.gnu.org/onlinedocs/gcc-9.2.0/gcc/PDP_002d11-Options.html