Thursday, September 19, 2024 Richard Sandiford <richard.sandif...@arm.com> wrote:
> abs_hwi (const_offset) (since const_offset has HOST_WIDE_INT type). abs_hwi has been applied. > It might be easier to pass base and const_offset from the caller > (aarch64_expand_mov_immediate). We are then guaranteed that the > offset is constant and don't need to worry about the SVE case. > The new SYM+OFF expression can be calculated using plus_constant. The implementation has been refactored to use plus_constant. > I think it'd be worth asserting that the offset fits in 32 bits, > since if by some bug the offset is larger, we'd generate silent > wrong code (in the sense that the compiler would truncate the offset > before the assembler sees it). The new implementation extends offset support from 1MB to 16MB and will not compile code with a larger offset. A 16MB offset is sufficient for our CI, however, the offset support will be extended to 4GB in the following patch series. > I think the normal addition patterns can handle this, if we pass the > result of the ~0xfffff calculation. There should be no need for a > dedicated pattern. Yes, it looks like it works as expected. > I think it'd be clearer to duplicate the gen_add_losym and avoid the > do...while(0) The code has been refactored to remove the use of do..while(0). The generated code is very similar to the original implementation: https://gcc.gnu.org/pipermail/gcc-patches/2024-September/662505.html. The difference is that "symbol + offset" is used for cases when the offset is less than 1MB, and only "symbol" without the offset is used when it is greater than or equal to 1MB. an offset < 1MB adrp x0, symbol+1048575 add x0, x0, :lo12:symbol+1048575 an offset >= 1MB adrp x0, symbol add x0, x0, :lo12:symbol add x0, x0, 1048576 ldrb w0, [x0, 4093] The original implementation might be more preferable and can be extended to use "symbol + offset" when the offset is less than 1MB. However, both options should be fine for now to handle offsets up to 16MB. Regards, Evgeny index ddaea4ab6e2..3f64182b3e4 100644 --- a/gcc/config/aarch64/aarch64.cc +++ b/gcc/config/aarch64/aarch64.cc @@ -2962,6 +2962,25 @@ aarch64_load_symref_appropriately (rtx dest, rtx imm, tmp_reg = gen_reg_rtx (mode); emit_move_insn (tmp_reg, gen_rtx_HIGH (mode, copy_rtx (imm))); + + if (TARGET_PECOFF) + { + poly_int64 offset; + HOST_WIDE_INT const_offset; + strip_offset (imm, &offset); + + if (offset.is_constant (&const_offset) + && abs_hwi (const_offset) >= 1 << 20) + { + rtx const_int = imm; + const_int = XEXP (const_int, 0); + XEXP (const_int, 1) = GEN_INT (const_offset % (1 << 20)); + + emit_set_insn (tmp_reg, plus_constant (mode, tmp_reg, + const_offset & ~0xfffff)); + } + } + emit_insn (gen_add_losym (dest, tmp_reg, imm)); return; }
