Hi,
GCC manuals says the foloowing are the list of
optimizations turned on when -O1 flag is used.
-------------------------------------------------------
-fdefer-pop -fdelayed-branch
-fguess-branch-probability -fcprop-registers
-floop-optimize -fif-conversion
-fif-conversion2 -ftree-ccp -ftree-dce
-ftree-dominator-opts -ftree-dse
-ftree-ter -ftree-lrs -ftree-sra
-ftree-copyrename -ftree-fre -ftree-ch
-fmerge-constants
-O also turns on -fomit-frame-pointer on
machines where doing so does not
interfere with debugging.
-O doesn?t turn on -ftree-sra for the Ada
compiler. This option must be
explicitly specified on the command line to
be enabled for the Ada compiler.
----------------------------------------------------
But When I compiled the same file as in the following
2 ways, I got two differen assembly programs. What
could be the reason.
Thanks in advance.
1) gcc -march=pentium4 -O1 -S res22.c
2) gcc -march=pentium4 -fdefer-pop -fdelayed-branch
-fguess-branch-probability -fcprop-registers
-floop-optimize -fif-conversion
-fif-conversion2 -ftree-ccp -ftree-dce
-ftree-dominator-opts -ftree-dse
-ftree-ter -ftree-lrs -ftree-sra
-ftree-copyrename -ftree-fre -ftree-ch
-fmerge-constants -fomit-frame-pointer
-ftree-sra
-S res22.c
Are there any extra optimizations turned on while
using -O1 options???????????????
Below is the res22.c program.
-------------------------------------------------------
-------------------------------------------------------
1 #include <stdio.h>
2 #include <xmmintrin.h>
3 unsigned int x , y,p,val,x1;
4
5 __m128 a, b, c;
6
7 float inp_sse1[4] __attribute__((aligned(16)))
= { 1.2, 3.5, 1.7, 2.8 };
8 float inp_sse2[4]
__attribute__((aligned(16)))= { -0.7, 2.6, 3.3, -4.0
};
9 float out_sse[4] __attribute__((aligned(16)));
10 void f()
11 {
12
13 c = _mm_add_ps(a, b);
14 _mm_store_ps(out_sse,c);
15 }
16
17
18 int main(void){
19 int i,j;
20
21 a = _mm_load_ps(inp_sse1);
22 b = _mm_load_ps(inp_sse2);
23
24 //for(j=0;j<999;j++)
25 // for(i = 0; i < 9999; i++)
26 f();
27
28 for(i = 0; i < 4; i++) {
29 printf("Result %d: %.2f\n",i,out_sse[i]);
30 }
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