On 2021-09-17 12:53:25 -0500, Segher Boessenkool wrote:
> For x86 -march=something is the same as -march=native, _if_ the compiler
> knows about your CPU.
It isn't:
cventin:~> diff -u <(gcc -Q --help=target --help=params -march=haswell) \
<(gcc -Q --help=target --help=params -march=native)
--- /proc/self/fd/11 2021-09-27 14:53:27.003263155 +0200
+++ /proc/self/fd/14 2021-09-27 14:53:27.003263155 +0200
@@ -9,11 +9,11 @@
-m8bit-idiv [disabled]
-m96bit-long-double [disabled]
-mabi= sysv
- -mabm [disabled]
+ -mabm [enabled]
-maccumulate-outgoing-args [disabled]
-maddress-mode= long
-madx [disabled]
- -maes [disabled]
+ -maes [enabled]
-malign-data= compat
-malign-double [disabled]
-malign-functions= 0
@@ -304,8 +304,8 @@
--param=jump-table-max-growth-ratio-for-size= 300
--param=jump-table-max-growth-ratio-for-speed= 800
--param=l1-cache-line-size= 64
- --param=l1-cache-size= 64
- --param=l2-cache-size= 512
+ --param=l1-cache-size= 32
+ --param=l2-cache-size= 15360
--param=large-function-growth= 100
--param=large-function-insns= 2700
--param=large-stack-frame-growth= 1000
I don't understand "_if_ the compiler knows about your CPU": if the
compiler knows about the CPU, it should select more accurate options
(as shown above, where abm and aes get enabled), shouldn't it?
--
Vincent Lefèvre <vincent@xxxxxxxxxx> - Web: <https://www.vinc17.net/>
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Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)
