[SubZero] Implement address optimization for MIPS

tests_lit/llvm2ice_tests/mips-address-mode-opt.ll

+; This file checks support for address mode optimization.
+; This test file is same as address-mode-opt.ll however the functions in this
+; file are relevant to MIPS only.
+
+; RUN: %if --need=target_MIPS32 --need=allow_dump \
+; RUN:   --command %p2i --filetype=asm --assemble --disassemble \
+; RUN:   --target mips32 -i %s --args -O2 --skip-unimplemented \
+; RUN:   -allow-externally-defined-symbols \
+; RUN:   | %if --need=target_MIPS32 --need=allow_dump \
+; RUN:     --command FileCheck --check-prefix MIPS32 %s
+
+define internal float @load_arg_plus_offset(float* %arg) {
+entry:
+  %arg.int = ptrtoint float* %arg to i32
+  %addr.int = add i32 %arg.int, 16
+  %addr.ptr = inttoptr i32 %addr.int to float*
+  %addr.load = load float, float* %addr.ptr, align 4
+  ret float %addr.load
+}
+; MIPS32-LABEL: load_arg_plus_offset
+; MIPS32: lwc1 $f0,16(a0)
+
+define internal float @load_arg_minus_offset(float* %arg) {
+entry:
+  %arg.int = ptrtoint float* %arg to i32
+  %addr.int = sub i32 %arg.int, 16
+  %addr.ptr = inttoptr i32 %addr.int to float*
+  %addr.load = load float, float* %addr.ptr, align 4
+  ret float %addr.load
+}
+; MIPS32-LABEL: load_arg_minus_offset
+; MIPS32 lwc1 $f0,-16(a0)
+
+define internal float @address_mode_opt_chaining(float* %arg) {
+entry:
+  %arg.int = ptrtoint float* %arg to i32
+  %addr1.int = add i32 12, %arg.int
+  %addr2.int = sub i32 %addr1.int, 4
+  %addr2.ptr = inttoptr i32 %addr2.int to float*
+  %addr2.load = load float, float* %addr2.ptr, align 4
+  ret float %addr2.load
+}
+; MIPS32-LABEL: address_mode_opt_chaining
+; MIPS32 lwc1 $f0,8(a0)