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gcc/resource.c mark_target_live_regs Question
- To: gcc at gcc dot gnu dot org
- Subject: gcc/resource.c mark_target_live_regs Question
- From: Jeffrey Oldham <oldham at codesourcery dot com>
- Date: Wed, 14 Feb 2001 16:09:57 -0800
- cc: oldham at codesourcery dot com, rth at redhat dot com, geoffk at redhat dot com
- Reply-to: oldham at codesourcery dot com
Why does resource.c's mark_target_live_regs() start computing live
registers at the previous BARRIER rather than the beginning of the
basic block containing the target? For functions with lots of
instructions but few BARRIERs, this can lead to O(n^2) performance
even if the function has many basic blocks.
Compiling gcc/testsuite/gcc.c-torture/compile/20001226-1.c with -O1,
-O2, or -O3 for mips-sgi-irix6.5 demonstrates the resulting slow
running time.
Thanks for the information,
Jeffrey D. Oldham
oldham@codesourcery.com