3 Commits

Author	SHA1	Message	Date
Benjamin Kramer	94f07f8c2c	InstCombine: Add a combine that turns (2^n)-1 ^ x back into (2^n)-1 - x iff x is smaller than 2^n and it fuses with a following add. ... This was intended to undo the sub canonicalization in cases where it's not profitable, but it also finds some cases on it's own. llvm-svn: 147256	2011-12-24 17:31:53 +00:00
Benjamin Kramer	b5e584392b	ComputeMaskedBits: Make knownzero computation more aggressive for ctlz with undef zero. ... unsigned foo(unsigned x) { return 31 - __builtin_clz(x); } now compiles into a single "bsrl" instruction on x86. llvm-svn: 147255	2011-12-24 17:31:46 +00:00
Benjamin Kramer	0b4d2e3d2a	InstCombine: Canonicalize (2^n)-1 - x into (2^n)-1 ^ x iff x is known to be smaller than 2^n. ... This has the obvious advantage of being commutable and is always a win on x86 because const - x wastes a register there. On less weird architectures this may lead to a regression because other arithmetic doesn't fuse with it anymore. I'll address that problem in a followup. llvm-svn: 147254	2011-12-24 17:31:38 +00:00