From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 14733 invoked by alias); 30 Mar 2006 16:15:00 -0000 Received: (qmail 14723 invoked by uid 48); 30 Mar 2006 16:14:57 -0000 Date: Thu, 30 Mar 2006 16:15:00 -0000 Subject: [Bug tree-optimization/26944] New: -ftree-ch generates worse code X-Bugzilla-Reason: CC Message-ID: Reply-To: gcc-bugzilla@gcc.gnu.org To: gcc-bugs@gcc.gnu.org From: "dann at godzilla dot ics dot uci dot edu" Mailing-List: contact gcc-bugs-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Archive: List-Post: List-Help: Sender: gcc-bugs-owner@gcc.gnu.org X-SW-Source: 2006-03/txt/msg02973.txt.bz2 List-Id: The loop from the code below is compiled to this when using gcc-4.1 -O2 .L5: movl 16(%ebp), %eax addl %ecx, %eax addl $1, %ecx movl %edx, 20(%ebx,%eax,4) leal (%edx,%ecx), %eax cmpl %edi, %eax jle .L5 but the code is much better when using gcc -fno-tree-ch -O2 .L3: addl $1, %ecx movl %ebx, -4(%edx) addl $4, %edx cmpl %eax, %ecx jle .L3 This is a regression as gcc-3.4.3 generates similar code. The code is from the Dhrystone as included in Unixbench. The regression is quite important as embedded processor people still use Dhrystone for benchmarking compiler/processor speed. Its strange that tree-ch messes up, the loop is about as simple as loops can get. typedef int One_Fifty; typedef int Arr_1_Dim [50]; typedef int Arr_2_Dim [50] [50]; extern int Int_Glob; void Proc_8 (Arr_1_Par_Ref, Arr_2_Par_Ref, Int_1_Par_Val, Int_2_Par_Val) Arr_1_Dim Arr_1_Par_Ref; Arr_2_Dim Arr_2_Par_Ref; int Int_1_Par_Val; int Int_2_Par_Val; { register One_Fifty Int_Index; register One_Fifty Int_Loc; Int_Loc = Int_1_Par_Val + 5; Arr_1_Par_Ref [Int_Loc] = Int_2_Par_Val; Arr_1_Par_Ref [Int_Loc+1] = Arr_1_Par_Ref [Int_Loc]; Arr_1_Par_Ref [Int_Loc+30] = Int_Loc; for (Int_Index = Int_Loc; Int_Index <= Int_Loc+1; ++Int_Index) Arr_2_Par_Ref [Int_Loc] [Int_Index] = Int_Loc; Arr_2_Par_Ref [Int_Loc] [Int_Loc-1] += 1; Arr_2_Par_Ref [Int_Loc+20] [Int_Loc] = Arr_1_Par_Ref [Int_Loc]; Int_Glob = 5; } Intel's compiler generates even tighter code: ..B1.7: # Preds ..B1.10 ..B1.7 movl %ebx, (%ecx,%edx,4) #20.5 addl $1, %edx #19.55 cmpl %eax, %edx #19.3 jle ..B1.7 # Prob 80% #19.3 -- Summary: -ftree-ch generates worse code Product: gcc Version: 4.1.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: tree-optimization AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: dann at godzilla dot ics dot uci dot edu GCC target triplet: i686-pc-linux-gnu http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26944