From a91c51c187a78e4164bc4039ebdb543848e379d2 Mon Sep 17 00:00:00 2001 From: Jeff Law Date: Thu, 11 Jul 2024 21:37:34 -0600 Subject: [PATCH] [committed] Fix m68k bootstrap segfault with late-combine So the m68k port has failed to bootstrap since the introduction of late-combine. My suspicion has been this is a backend problem. Sure enough after bisecting things down (thank goodness for the debug counter!) I'm happy to report m68k (after this patch) has moved into its stage3 build for the first time in a month. Basically late-combine propagated an address calculation to its use points, generating this insn (dwarf2out.c, I forget what function): > (insn 653 652 655 (parallel [ > (set (mem/j:DI (plus:SI (plus:SI (reg/f:SI 9 %a1 [orig:64 _67 ] [64]) > (reg:SI 0 %d0 [321])) > (const_int 20 [0x14])) [0 slot_204->dw_attr_val.v.val_unsigned+0 S8 A16]) > (sign_extend:DI (mem/c:SI (plus:SI (reg/f:SI 14 %a6) > (const_int -28 [0xffffffffffffffe4])) [870 %sfp+-28 S4 A16]))) > (clobber (reg:SI 0 %d0)) > ]) "../../../gcc/gcc/dwarf2out.cc":24961:23 93 {extendsidi2} > (expr_list:REG_DEAD (reg/f:SI 9 %a1 [orig:64 _67 ] [64]) > (expr_list:REG_DEAD (reg:SI 0 %d0 [321]) > (expr_list:REG_UNUSED (reg:SI 0 %d0) > (nil))))) Note how the output uses d0 in the address calculation and the clobber uses d0. It matches this insn in the md file: > (define_insn "extendsidi2" > [(set (match_operand:DI 0 "nonimmediate_operand" "=d,o,o,<") > (sign_extend:DI > (match_operand:SI 1 "nonimmediate_src_operand" "rm,rm,r,rm"))) > (clobber (match_scratch:SI 2 "=X,&d,&d,&d"))] > "" > { > if (which_alternative == 0) > /* Handle alternative 0. */ > { > if (TARGET_68020 || TARGET_COLDFIRE) > return "move%.l %1,%R0\;smi %0\;extb%.l %0"; > else > return "move%.l %1,%R0\;smi %0\;ext%.w %0\;ext%.l %0"; > } > > /* Handle alternatives 1, 2 and 3. We don't need to adjust address by 4 > in alternative 3 because autodecrement will do that for us. */ > operands[3] = adjust_address (operands[0], SImode, > which_alternative == 3 ? 0 : 4); > operands[0] = adjust_address (operands[0], SImode, 0); > > if (TARGET_68020 || TARGET_COLDFIRE) > return "move%.l %1,%3\;smi %2\;extb%.l %2\;move%.l %2,%0"; > else > return "move%.l %1,%3\;smi %2\;ext%.w %2\;ext%.l %2\;move%.l %2,%0"; > } > [(set_attr "ok_for_coldfire" "yes,no,yes,yes")]) Note the smi/ext instruction pair in the case for alternatives 1..3. Those clobber the scratch register before we're done consuming inputs. The scratch register really needs to be marked as an earlyclobber. That fixes the bootstrap problem, but a cursory review of m68k.md is not encouraging. I will not be surprised at all if there's more of this kind of problem lurking. But happy to at least have m68k bootstrapping again. It's failing the comparison test, but definitely progress. * config/m68k/m68k.md (extendsidi2): Add missing early clobbers. --- gcc/config/m68k/m68k.md | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/gcc/config/m68k/m68k.md b/gcc/config/m68k/m68k.md index 037978db40c..e5c25288844 100644 --- a/gcc/config/m68k/m68k.md +++ b/gcc/config/m68k/m68k.md @@ -1887,7 +1887,7 @@ [(set (match_operand:DI 0 "nonimmediate_operand" "=d,o,o,<") (sign_extend:DI (match_operand:SI 1 "nonimmediate_src_operand" "rm,rm,r,rm"))) - (clobber (match_scratch:SI 2 "=X,d,d,d"))] + (clobber (match_scratch:SI 2 "=X,&d,&d,&d"))] "" { if (which_alternative == 0)