https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69633
Bug ID: 69633
Summary: [6 Regression] Redundant move is generated after
r228097
Product: gcc
Version: 6.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: rtl-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: ysrumyan at gmail dot com
Target Milestone: ---
Sorry, that we noticed this regression just now but not in September.
After Makarov's fix for 61578 ( and s390 regression) we noticed that for
attached simple test-case extracted from real benchmark one more redundant move
instruction is generated (till 20160202 compiler build):
before fix (postreload dump)
86: NOTE_INSN_BASIC_BLOCK 4
40: dx:QI=[si:SI]
41: ax:QI=[si:SI+0x1]
42: {si:SI=si:SI+0x3;clobber flags:CC;}
43: dx:SI=zero_extend(dx:QI)
44: ax:SI=zero_extend(ax:QI)
45: cx:SI=zero_extend([si:SI-0x1])
46: {di:SI=dx:SI*0x4c8b;clobber flags:CC;}
47: {bx:SI=ax:SI*0x9646;clobber flags:CC;}
48: {bx:SI=bx:SI+di:SI;clobber flags:CC;}
49: {di:SI=cx:SI*0x1d2f;clobber flags:CC;}
50: NOTE_INSN_DELETED
51: bx:SI=bx:SI+di:SI+0x8000
52: {bx:SI=bx:SI>>0x10;clobber flags:CC;}
53: [bp:SI]=bx:QI
96: bx:SI=dx:SI
55: {bx:SI=bx:SI<<0xf;clobber flags:CC;}
57: {bx:SI=bx:SI-dx:SI;clobber flags:CC;}
after fix
86: NOTE_INSN_BASIC_BLOCK 4
40: dx:QI=[si:SI]
41: ax:QI=[si:SI+0x1]
42: {si:SI=si:SI+0x3;clobber flags:CC;}
43: dx:SI=zero_extend(dx:QI)
44: ax:SI=zero_extend(ax:QI)
45: cx:SI=zero_extend([si:SI-0x1])
46: {di:SI=dx:SI*0x4c8b;clobber flags:CC;}
47: {bx:SI=ax:SI*0x9646;clobber flags:CC;}
48: {bx:SI=bx:SI+di:SI;clobber flags:CC;}
49: {di:SI=cx:SI*0x1d2f;clobber flags:CC;}
50: NOTE_INSN_DELETED
51: bx:SI=bx:SI+di:SI+0x8000
52: {bx:SI=bx:SI>>0x10;clobber flags:CC;}
53: [bp:SI]=bx:QI
96: bx:SI=dx:SI
55: {bx:SI=bx:SI<<0xf;clobber flags:CC;}
98: di:SI=bx:SI !! redundnat move
57: {di:SI=di:SI-dx:SI;clobber flags:CC;}
In result, we got >3% slowdown on Silvermont in pie & 32-bit mode.
