https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64154
--- Comment #3 from vries at gcc dot gnu.org --- (In reply to Terry Guo from comment #2) > Hi Tom, > > I enabled this optimization to thumb1 target cortex-m0 Does that mean you just reverted the patch for PR63718? > and found this IPA-RA > optimization doesn't consider the register clobber information attached to > call rtx The IPA-RA analysis does consider that clobber. It's using find_all_hard_reg_sets, and that function contains a loop over CALL_INSN_FUNCTION_USAGE. > and thus generated bad code. Here are the bad rtxs I extracted from > the dump of cprop_hardreg pass: > > (insn 292 291 141 13 (set (reg:SI 4 r4 [orig:163 ivtmp.108 ] [163]) > (reg:SI 12 ip [orig:163 ivtmp.108 ] [163])) 742 {*thumb1_movsi_insn} > (expr_list:REG_DEAD (reg:SI 12 ip [orig:163 ivtmp.108 ] [163]) > (nil))) > > (call_insn 141 292 142 13 (parallel [ > (call (mem:SI (symbol_ref:SI ("f2") [flags 0x3] <function_decl > 0x7f8182689100 f2>) [0 f2 S4 A32]) > (const_int 0 [0])) > (use (const_int 0 [0])) > (clobber (reg:SI 14 lr)) > ]) > /myssd/terguo01/toolchain-build/GCC32RM-424/src/gcc/gcc/testsuite/gcc.dg/ > vshift-3.c:119 770 {*call_insn} > (expr_list:REG_CALL_DECL (symbol_ref:SI ("f2") [flags 0x3] > <function_decl 0x7f8182689100 f2>) > (expr_list:REG_EH_REGION (const_int 0 [0]) > (nil))) > (expr_list (clobber (reg:SI 12 ip)) > (nil))) > > (insn 11 10 12 13 (set (reg:SI 0 r0 [orig:170 ivtmp.130 ] [170]) > (reg:SI 12 ip [orig:163 ivtmp.108 ] [163])) > /myssd/terguo01/toolchain-build/GCC32RM-424/src/gcc/gcc/testsuite/gcc.dg/ > vshift-3.c:121 742 {*thumb1_movsi_insn} > (expr_list:REG_EQUAL (symbol_ref:SI ("j") [flags 0x80] <var_decl > 0x7f81827d0750 j>) > (nil))) > That is wrong indeed: ip is explicitly clobbered by the call in CALL_INSN_FUNCTION_USAGE, but used as if not clobbered by the call. > I checked the code in 'if (CALL_P (insn))' part in file regcprop.c and found > the algorithm doesn't consider the '(expr_list (clobber (reg:SI 12 ip))' in > insn 141 which makes current algorithm think it is safe to propagate ip from > insn 292 to insn 11. > I cannot reproduce the wrong code as listed above. But I can reproduce the clobber being skipped by copyprop_hardreg_forward_1. So I agree, cprop_hardreg does not respect the clobber on the call in CALL_INSN_FUNCTION_USAGE. I'll file a PR.