On 27/08/14 11:08, Bin Cheng wrote: > Hi > As reported in bug pr62151, combine pass may wrongly delete necessary > instruction in function distribute_notes thus leaving register > uninitialized. This patch is to fix the issue by checking if i2 immediately > modifies the register in REG_DEAD note. If yes, set tem_insn accordingly to > start finding right place for note distribution from i2. > > I once sent a RFC patch at > https://gcc.gnu.org/ml/gcc-patches/2014-08/msg01718.html, but got no > comments, here I added some comments in this patch to make it a formal one. > > > I tested the original patch, and will re-test it against the latest code > later. So is it OK? Any comments will be appreciated. >
Isn't this the sort of sequence that combinable_i3pat is supposed to reject? R. > Thanks, > bin > > 2014-08-27 Bin Cheng <bin.ch...@arm.com> > > PR rtl-optimization/62151 > * combine.c (distribute_notes): Check i2 if it modifies register > in REG_DEAD note immediately, set tem_insn accordingly. > > > pr62151-20140827.txt > > > Index: gcc/combine.c > =================================================================== > --- gcc/combine.c (revision 214413) > +++ gcc/combine.c (working copy) > @@ -13499,7 +13499,38 @@ distribute_notes (rtx notes, rtx_insn *from_insn, > || rtx_equal_p (XEXP (note, 0), elim_i1) > || rtx_equal_p (XEXP (note, 0), elim_i0)) > break; > - tem_insn = i3; > + > + /* See PR62151. > + It's possible to have below situation: > + i0: r1 <- const_0 > + i1: r2 <- r1 op_1 const_1 > + REG_DEAD r1 > + i2: r1 <- r2 op_2 const_2 > + REG_DEAD r2 > + i3: r3 <- r1 > + i4: r4 <- r1 > + > + It is transformed into below code before distributing > + the REG_DEAD note in i1: > + i0: NOTE_INSN_DELETED > + i1: NOTE_INSN_DELETED > + i2: r1 <- const_combined > + i3: r3 <- const_combined > + i4: r4 <- r1 > + > + We need to check if i2 immediately modifies r1 otherwise > + i2 would be deleted by below code when distributing > + REG_DEAD note, leaving r1 in i4 uninitialied. > + > + We set TEM_INSN to i2 for this case indicating that we > + need to find right place for distribution from i2. > + */ > + if (from_insn && i2 > + && from_insn != i2 && from_insn != i3 > + && reg_set_p (XEXP (note, 0), PATTERN (i2))) > + tem_insn = i2; > + else > + tem_insn = i3; > } > > if (place == 0) >
