On Sun, Jan 19, 2014 at 3:20 PM, H.J. Lu <hjl.to...@gmail.com> wrote:
>>> For LEA operation with SImode_address_operand, which zero-extends SImode >>> to DImode, ix86_split_lea_for_addr turns >>> >>> (set (reg:DI) ...) >>> >>> into >>> >>> (set (reg:SI) ...) >>> >>> We need to do >>> >>> (set (reg:DI) (zero_extend:DI (reg:SI))) >>> >>> at the end. If the LEA operation is >>> >>> (set (reg:DI) (zero_extend:DI (reg:SI))) >> >> ree pass should remove these. However, we can just emit zero-extend >> insn at the end of sequence, and ree (which is located after >> post-reload split) should handle it: >> >> --cut here-- >> Index: config/i386/i386.md >> =================================================================== >> --- config/i386/i386.md (revision 206753) >> +++ config/i386/i386.md (working copy) >> @@ -5428,12 +5428,17 @@ >> operands[0] = SET_DEST (pat); >> operands[1] = SET_SRC (pat); >> >> - /* Emit all operations in SImode for zero-extended addresses. Recall >> - that x86_64 inheretly zero-extends SImode operations to DImode. */ >> + /* Emit all operations in SImode for zero-extended addresses. */ >> if (SImode_address_operand (operands[1], VOIDmode)) >> mode = SImode; >> >> ix86_split_lea_for_addr (curr_insn, operands, mode); >> + >> + /* Zero-extend return register to DImode for zero-extended addresses. */ >> + if (mode != <MODE>mode) >> + emit_insn (gen_zero_extendsidi2 >> + (operands[0], gen_lowpart ((mode), operands[0]))); >> + >> DONE; >> } >> [(set_attr "type" "lea") >> --cut here-- >> >> The patch was tested with a testcase from Comment #9 of the PR using >> "-O --march=corei7 -mtune=slm", and resulting binary runs without >> problems. >> > > Yes, the resulting GCC works correctly. However, we generate > extra > > (set (reg:DI) (zero_extend:DI (reg:SI))) > > It is because we generate > > (set (reg:SI) (reg:SI) > (set (reg:DI) (zero_extend:DI (reg:SI))) > > REE pass doesn't know > > (set (reg:SI) (reg:SI) > > has an implicit ZERO_EXTEND. Here is a testcase: This is the correct sequence,and REE pass should be improved to handle this situation. Note, that the problem was that we assumed SImode operations (including move) have implicit DImode zero-extend, but in fact we haven't communicate this to the compiler in a proper way. So, I propose we go with my patch and file an enhancement PR for the REE pass. Uros.
