2 Commits

Author	SHA1	Message	Date
Roman Lebedev	8360c42e25	[InstCombine] foldICmpBinOp(): consider inverted check in 'unsigned sub overflow' check ... A follow-up for r329011. This may be changed to produce @llvm.sub.with.overflow in a later patch, but for now just make things more consistent overall. A few observations stem from this: * There does not seem to be a similar one-instruction fold for uadd-overflow * I'm not sure we'll want to canonicalize `B u> A` as `usub.with.overflow`, so since the `icmp` here no longer refers to `sub`, reconstructing `usub.with.overflow` will be problematic, and will likely require standalone pass (similar to DivRemPairs). https://rise4fun.com/Alive/Zqs Name: (A - B) u> A --> B u> A %t0 = sub i8 %A, %B %r = icmp ugt i8 %t0, %A => %r = icmp ugt i8 %B, %A Name: (A - B) u<= A --> B u<= A %t0 = sub i8 %A, %B %r = icmp ule i8 %t0, %A => %r = icmp ule i8 %B, %A Name: C u< (C - D) --> C u< D %t0 = sub i8 %C, %D %r = icmp ult i8 %C, %t0 => %r = icmp ult i8 %C, %D Name: C u>= (C - D) --> C u>= D %t0 = sub i8 %C, %D %r = icmp uge i8 %C, %t0 => %r = icmp uge i8 %C, %D llvm-svn: 371101	2019-09-05 17:41:02 +00:00
Roman Lebedev	1d9e0dcc9d	[InstCombine][NFC] Tests for 'unsigned sub overflow' check ... ---------------------------------------- Name: unsigned sub, overflow, v0 %sub = sub i8 %x, %y %ov = icmp ugt i8 %sub, %x => %agg = usub_overflow i8 %x, %y %sub = extractvalue {i8, i1} %agg, 0 %ov = extractvalue {i8, i1} %agg, 1 Done: 1 Optimization is correct! ---------------------------------------- Name: unsigned sub, no overflow, v0 %sub = sub i8 %x, %y %ov = icmp ule i8 %sub, %x => %agg = usub_overflow i8 %x, %y %sub = extractvalue {i8, i1} %agg, 0 %not.ov = extractvalue {i8, i1} %agg, 1 %ov = xor %not.ov, -1 Done: 1 Optimization is correct! llvm-svn: 371099	2019-09-05 17:40:37 +00:00