https://gcc.gnu.org/bugzilla/show_bug.cgi?id=55190
Alan Modra <amodra at gmail dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target|sh*-*-* arm*-*-* |sh*-*-* arm*-*-*
| |powerpc*-*-*
CC| |amodra at gmail dot com
--- Comment #10 from Alan Modra <amodra at gmail dot com> ---
Seen also on powerpc. Even for simple testcases like
int b[30];
void
fn1 (unsigned int n)
{
unsigned int i;
for (i = 0; i < n; i++)
b[i] = 42;
}
I see for -m32
fn1:
cmpwi 0,3,0
beq 0,.L1
slwi 9,3,2 ####
lis 10,b-4@ha
addi 9,9,-4 ####
la 10,b-4@l(10)
srwi 9,9,2 ####
li 8,42
addi 9,9,1 ####
mtctr 9
.p2align 4,,15
.L3:
stwu 8,4(10)
bdnz .L3
.L1:
blr
All of the insns marked #### are redundant.
For -m64 this loop doesn't even use bdnz
Loop 1 is simple:
simple exit 4 -> 5
infinite if: (expr_list:REG_DEP_TRUE (ne:SI (and:DI (plus:DI (minus:DI
(ashift:DI (reg:DI 189)
(const_int 2 [0x2]))
(reg:DI 179 [ ivtmp.7 ]))
(symbol_ref:DI ("b") [flags 0x80] <var_decl 0x7fe7521de870
b>))
(const_int 3 [0x3]))
(const_int 0 [0]))
(nil))
number of iterations: (lshiftrt:DI (plus:DI (minus:DI (reg:DI 185 [ _18 ])
(reg:DI 179 [ ivtmp.7 ]))
(const_int -4 [0xfffffffffffffffc]))
(const_int 2 [0x2]))
upper bound: 29
likely upper bound: 29
realistic bound: -1
Doloop: Possible infinite iteration case.
Doloop: The loop is not suitable.
