matmul: play with alignment, attempt block mult, but it is slow so likely wrong

Author: cirosantilli

gcc/attribute.c

@@ -394,11 +394,22 @@ int main() {
 
             Aligns variables on X bit lines.
 
-            This may be required for certain processor specific functions.
+            This may be required for certain processor specific functions, in particular SIMD operations.
 
             The generated gas assembly code should mark this alignment with the `.align` directive.
 
             http://stackoverflow.com/questions/381244/purpose-of-memory-alignment
+
+            C11 has aligned_alloc:
+
+			- http://stackoverflow.com/questions/227897/how-to-allocate-aligned-memory-only-using-the-standard-library
+			- http://stackoverflow.com/questions/3839922/aligned-malloc-in-gcc
+
+			Assume that function argument pointer is aligned:
+			http://stackoverflow.com/questions/9608171/how-to-tell-gcc-that-a-pointer-argument-is-always-double-word-aligned
+
+			TODO does it work for stack variables?
+			http://stackoverflow.com/questions/841433/are-stack-variables-aligned-by-the-gcc-attribute-alignedx
         */
         {
             assert(aligned16 == 0);

gcc/vector.c

@@ -5,6 +5,8 @@ Basically a more abstract and ISA portable (TODO?) version of intrinsics.
 
 Note however that the GCC and other compiles have an auto-vectorization
 optimization, which might use SIMD even if you don't use the vector extensions.
+
+TODO: is explicit alignment attribute necessary, or automatically done?
 */
 
 #include "common.h"