1 Commits

Author	SHA1	Message	Date
Marina Yatsina	f9371d821f	Add logic to greedy reg alloc to avoid bad eviction chains ... This fixes bugzilla 26810 https://bugs.llvm.org/show_bug.cgi?id=26810 This is intended to prevent sequences like: movl %ebp, 8(%esp) # 4-byte Spill movl %ecx, %ebp movl %ebx, %ecx movl %edi, %ebx movl %edx, %edi cltd idivl %esi movl %edi, %edx movl %ebx, %edi movl %ecx, %ebx movl %ebp, %ecx movl 16(%esp), %ebp # 4 - byte Reload Such sequences are created in 2 scenarios: Scenario #1: vreg0 is evicted from physreg0 by vreg1 Evictee vreg0 is intended for region splitting with split candidate physreg0 (the reg vreg0 was evicted from) Region splitting creates a local interval because of interference with the evictor vreg1 (normally region spliiting creates 2 interval, the "by reg" and "by stack" intervals. Local interval created when interference occurs.) one of the split intervals ends up evicting vreg2 from physreg1 Evictee vreg2 is intended for region splitting with split candidate physreg1 one of the split intervals ends up evicting vreg3 from physreg2 etc.. until someone spills Scenario #2 vreg0 is evicted from physreg0 by vreg1 vreg2 is evicted from physreg2 by vreg3 etc Evictee vreg0 is intended for region splitting with split candidate physreg1 Region splitting creates a local interval because of interference with the evictor vreg1 one of the split intervals ends up evicting back original evictor vreg1 from physreg0 (the reg vreg0 was evicted from) Another evictee vreg2 is intended for region splitting with split candidate physreg1 one of the split intervals ends up evicting vreg3 from physreg2 etc.. until someone spills As compile time was a concern, I've added a flag to control weather we do cost calculations for local intervals we expect to be created (it's on by default for X86 target, off for the rest). Differential Revision: https://reviews.llvm.org/D35816 Change-Id: Id9411ff7bbb845463d289ba2ae97737a1ee7cc39 llvm-svn: 316295	2017-10-22 17:59:38 +00:00