[EMAIL PROTECTED]:~/ctest% cat see.c
int f37(int t, int seg) {
if (seg) t = (t + t + 1 + 32) << (seg + 2);
else t = (t + t + 1 ) << 3;
return t;
}
[EMAIL PROTECTED]:~/ctest% gcc -c -O3 -fno-see see.c && objdump -dr see.o >!
no-see.s
&& gcc -c -O3 -fsee see.c && objdump -dr see.o >! see.s && diff -u10 no-see.s
see.s
--- no-see.s 2006-05-07 10:49:20.000000000 +0200
+++ see.s 2006-05-07 10:49:20.000000000 +0200
@@ -2,17 +2,17 @@
see.o: file format elf64-alpha
Disassembly of section .text:
0000000000000000 <f37>:
0: 01 04 10 42 addq a0,a0,t0
4: 02 00 51 20 lda t1,2(a1)
8: 50 16 21 40 s8addq t0,0x8,a0
c: 21 00 21 20 lda t0,33(t0)
10: 21 07 22 48 sll t0,t1,t0
- 14: 00 00 f0 43 sextl a0,v0
+ 14: 00 04 f0 47 mov a0,v0
18: 01 00 20 e6 beq a1,20 <f37+0x20>
- 1c: 00 00 e1 43 sextl t0,v0
- 20: 01 80 fa 6b ret
- 24: 00 00 fe 2f unop
+ 1c: 00 04 e1 47 mov t0,v0
+ 20: 00 00 e0 43 sextl v0,v0
+ 24: 01 80 fa 6b ret
28: 1f 04 ff 47 nop
2c: 00 00 fe 2f unop
It looks like SEE correctly recognized that the sign extension after the shift
has to be done only once. However, it also introduces two spurious movs.
--
Summary: -fsee introduces spurious movs
Product: gcc
Version: 4.2.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: normal
Priority: P3
Component: tree-optimization
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: falk at debian dot org
GCC build triplet: alphaev68-unknown-linux-gnu
GCC host triplet: alphaev68-unknown-linux-gnu
GCC target triplet: alphaev68-unknown-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27467
