3 Commits

Author	SHA1	Message	Date
Dan Gohman	ad3e549a53	Implement support for using modeling implicit-zero-extension on x86-64 ... with SUBREG_TO_REG, teach SimpleRegisterCoalescing to coalesce SUBREG_TO_REG instructions (which are similar to INSERT_SUBREG instructions), and teach the DAGCombiner to take advantage of this on targets which support it. This eliminates many redundant zero-extension operations on x86-64. This adds a new TargetLowering hook, isZExtFree. It's similar to isTruncateFree, except it only applies to actual definitions, and not no-op truncates which may not zero the high bits. Also, this adds a new optimization to SimplifyDemandedBits: transform operations like x+y into (zext (add (trunc x), (trunc y))) on targets where all the casts are no-ops. In contexts where the high part of the add is explicitly masked off, this allows the mask operation to be eliminated. Fix the DAGCombiner to avoid undoing these transformations to eliminate casts on targets where the casts are no-ops. Also, this adds a new two-address lowering heuristic. Since two-address lowering runs before coalescing, it helps to be able to look through copies when deciding whether commuting and/or three-address conversion are profitable. Also, fix a bug in LiveInterval::MergeInClobberRanges. It didn't handle the case that a clobber range extended both before and beyond an existing live range. In that case, multiple live ranges need to be added. This was exposed by the new subreg coalescing code. Remove 2008-05-06-SpillerBug.ll. It was bugpoint-reduced, and the spiller behavior it was looking for no longer occurrs with the new instruction selection. llvm-svn: 68576	2009-04-08 00:15:30 +00:00
Evan Cheng	c2f95b56db	Minor optimization: ... Look for situations like this: %reg1024<def> = MOV r1 %reg1025<def> = MOV r0 %reg1026<def> = ADD %reg1024, %reg1025 r0 = MOV %reg1026 Commute the ADD to hopefully eliminate an otherwise unavoidable copy. llvm-svn: 65752	2009-03-01 02:03:43 +00:00
Evan Cheng	abda665f5f	Teach 2addr pass to be do more commuting. If both uses of a two-address instruction are killed, but the first operand has a use before and after the def, commute if the second operand does not suffer from the same issue. ... %reg1028<def> = EXTRACT_SUBREG %reg1027<kill>, 1 %reg1029<def> = MOV8rr %reg1028 %reg1029<def> = SHR8ri %reg1029, 7, %EFLAGS<imp-def,dead> insert => %reg1030<def> = MOV8rr %reg1028 %reg1030<def> = ADD8rr %reg1028<kill>, %reg1029<kill>, %EFLAGS<imp-def,dead> In this case, it might not be possible to coalesce the second MOV8rr instruction if the first one is coalesced. So it would be profitable to commute it: %reg1028<def> = EXTRACT_SUBREG %reg1027<kill>, 1 %reg1029<def> = MOV8rr %reg1028 %reg1029<def> = SHR8ri %reg1029, 7, %EFLAGS<imp-def,dead> insert => %reg1030<def> = MOV8rr %reg1029 %reg1030<def> = ADD8rr %reg1029<kill>, %reg1028<kill>, %EFLAGS<imp-def,dead> llvm-svn: 62954	2009-01-25 03:53:59 +00:00