[linux-kernel] Don't add -O3 to CFLAGS

It is no longer necessary to get good performance, there is only a small
speed difference between -O2 and -O3, so just stick to the default of
-O2.

This also fixes the stack space usage on parisc. The compiler was buggy
for -O3 and used ~3KB of stack space for several functions. With -O2 the
problem is completely resolved, and stack space is back to a few hundred
bytes.

Additionally, we get a large code size win on gcc:

| Compiler | Before (Bytes) | After (Bytes) | Delta (Bytes) |
|----------|----------------|---------------|---------------|
| gcc-11   |         952754 |        738954 |       -213800 |
| clang-12 |         976290 |        938826 |        -37464 |

diff --git a/contrib/linux-kernel/linux.mk b/contrib/linux-kernel/linux.mk
index 65218ec5b8f2a4e506796a755143513f6922a3c9..fc45339fc3a3659e56d112979891a619f8b862cb 100644 (file)
--- a/contrib/linux-kernel/linux.mk
+++ b/contrib/linux-kernel/linux.mk
@@ -11,8 +11,6 @@
 obj-$(CONFIG_ZSTD_COMPRESS) += zstd_compress.o
 obj-$(CONFIG_ZSTD_DECOMPRESS) += zstd_decompress.o
 
-ccflags-y += -O3
-
 zstd_compress-y := \
                zstd_compress_module.o \
                common/debug.o \