Changes in directory llvm/lib/Target/X86:
README.txt updated: 1.22 -> 1.23 --- Log message: transfer some notes from my email to somewhere useful. --- Diffs of the changes: (+45 -0) README.txt | 45 +++++++++++++++++++++++++++++++++++++++++++++ 1 files changed, 45 insertions(+) Index: llvm/lib/Target/X86/README.txt diff -u llvm/lib/Target/X86/README.txt:1.22 llvm/lib/Target/X86/README.txt:1.23 --- llvm/lib/Target/X86/README.txt:1.22 Thu Jan 12 19:20:42 2006 +++ llvm/lib/Target/X86/README.txt Mon Jan 16 11:52:31 2006 @@ -54,6 +54,10 @@ fucomi jl X jg X +Ideas: +http://gcc.gnu.org/ml/gcc-patches/2004-11/msg02410.html + + //===---------------------------------------------------------------------===// Improvements to the multiply -> shift/add algorithm: @@ -121,3 +125,44 @@ setg %al testb %al, %al # unnecessary jne .BB7 + +//===---------------------------------------------------------------------===// + +Count leading zeros and count trailing zeros: + +int clz(int X) { return __builtin_clz(X); } +int ctz(int X) { return __builtin_ctz(X); } + +$ gcc t.c -S -o - -O3 -fomit-frame-pointer -masm=intel +clz: + bsr %eax, DWORD PTR [%esp+4] + xor %eax, 31 + ret +ctz: + bsf %eax, DWORD PTR [%esp+4] + ret + +however, check that these are defined for 0 and 32. Our intrinsics are, GCC's +aren't. + +//===---------------------------------------------------------------------===// + +Use push/pop instructions in prolog/epilog sequences instead of stores off +ESP (certain code size win, perf win on some [which?] processors). + +//===---------------------------------------------------------------------===// + +Only use inc/neg/not instructions on processors where they are faster than +add/sub/xor. They are slower on the P4 due to only updating some processor +flags. + +//===---------------------------------------------------------------------===// + +Open code rint,floor,ceil,trunc: +http://gcc.gnu.org/ml/gcc-patches/2004-08/msg02006.html +http://gcc.gnu.org/ml/gcc-patches/2004-08/msg02011.html + +//===---------------------------------------------------------------------===// + +Combine: a = sin(x), b = cos(x) into a,b = sincos(x). + _______________________________________________ llvm-commits mailing list llvm-commits@cs.uiuc.edu http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
