clang-p2996

Files

Sanjay Patel 40b752d28d [InstCombine] fold icmp slt/sgt of offset value with constant

This follows up patches for the unsigned siblings:
0c400e8953
c7b658aeb5

We are translating an offset signed compare to its
unsigned equivalent when one end of the range is
at the limit (zero or unsigned max).

(X + C2) >s C --> X <u (SMAX - C) (if C == C2 - 1)
(X + C2) <s C --> X >u (C ^ SMAX) (if C == C2)

This probably does not show up much in IR derived
from C/C++ source because that would likely have
'nsw', and we have folds for that already.

As with the previous unsigned transforms, the folds
could be generalized to handle non-constant patterns:

https://alive2.llvm.org/ce/z/Y8Xrrm

  ; sgt
  define i1 @src(i8 %a, i8 %c) {
    %c2 = add i8 %c, 1
    %t = add i8 %a, %c2
    %ov = icmp sgt i8 %t, %c
    ret i1 %ov
  }

  define i1 @tgt(i8 %a, i8 %c) {
    %c_off = sub i8 127, %c ; SMAX
    %ov = icmp ult i8 %a, %c_off
    ret i1 %ov
  }

https://alive2.llvm.org/ce/z/c8uhnk

  ; slt
  define i1 @src(i8 %a, i8 %c) {
    %t = add i8 %a, %c
    %ov = icmp slt i8 %t, %c
    ret i1 %ov
  }

  define i1 @tgt(i8 %a, i8 %c) {
    %c_offnot = xor i8 %c, 127 ; SMAX
    %ov = icmp ugt i8 %a, %c_offnot
    ret i1 %ov
  }

2021-07-05 10:08:31 -04:00

CMakeLists.txt

llvmbuildectomy - replace llvm-build by plain cmake

2020-11-13 10:35:24 +01:00

InstCombineAddSub.cpp

[InstCombine] fix nsz (fast-math) propagation from fneg-of-select

2021-06-08 17:04:30 -04:00

InstCombineAndOrXor.cpp

[InstCombine] InstCombinerImpl::visitOr - enable bitreverse matching

2021-05-15 13:39:09 +01:00

InstCombineAtomicRMW.cpp

…