[all-commits] [llvm/llvm-project] e86eff: [InstSimplify] fold and/or of compares with equali...

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  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: e86eff0e82d1339956f1ed2a13dc89231fb2c3c8
      https://github.com/llvm/llvm-project/commit/e86eff0e82d1339956f1ed2a13dc89231fb2c3c8
  Author: Sanjay Patel <spatel at rotateright.com>
  Date:   2020-04-23 (Thu, 23 Apr 2020)

  Changed paths:
    M llvm/lib/Analysis/InstructionSimplify.cpp
    M llvm/test/Transforms/InstCombine/and-or-icmp-min-max.ll
    M llvm/test/Transforms/InstSimplify/and-or-icmp-min-max.ll
    M llvm/test/Transforms/InstSimplify/and-or-icmp-nullptr.ll

  Log Message:
  -----------
  [InstSimplify] fold and/or of compares with equality to min/max constant

I found 12 (6 if we compress the DeMorganized forms) patterns for logic-of-compares
with a min/max constant while looking at PR45510:
https://bugs.llvm.org/show_bug.cgi?id=45510

The variations on those forms multiply the test cases by 8 (unsigned/signed, swapped
compare operands, commuted logic operands).
We have partial logic to deal with these for the unsigned min (zero) case, but
missed everything else.

We are deferring the majority of these patterns to InstCombine to allow more general
handling (see D78582).

We could use ConstantRange instead of predicate+constant matching here. I don't
expect there's any noticeable compile-time impact for either form.

Here's an abuse of Alive2 to show the 12 basic signed variants of the patterns in
one function:
http://volta.cs.utah.edu:8080/z/5Vpiyg

declare void @use(i1, i1, i1, i1, i1, i1, i1, i1, i1, i1, i1, i1)
define void @src(i8 %x, i8 %y)  {
  %m1 = icmp eq i8 %x, 127
  %c1 = icmp slt i8 %x, %y
  %r1 = and i1 %m1, %c1   ; (X == MAX) && (X < Y) --> false

  %m2 = icmp ne i8 %x, 127
  %c2 = icmp sge i8 %x, %y
  %r2 = or i1 %m2, %c2    ; (X != MAX) || (X >= Y) --> true

  %m3 = icmp eq i8 %x, -128
  %c3 = icmp sgt i8 %x, %y
  %r3 = and i1 %m3, %c3   ; (X == MIN) && (X > Y) --> false

  %m4 = icmp ne i8 %x, -128
  %c4 = icmp sle i8 %x, %y
  %r4 = or i1 %m4, %c4    ; (X != MIN) || (X <= Y) --> true

  %m5 = icmp eq i8 %x, 127
  %c5 = icmp sge i8 %x, %y
  %r5 = and i1 %m5, %c5   ; (X == MAX) && (X >= Y) --> X == MAX

  %m6 = icmp ne i8 %x, 127
  %c6 = icmp slt i8 %x, %y
  %r6 = or i1 %m6, %c6   ; (X != MAX) || (X < Y) --> X != MAX

  %m7 = icmp eq i8 %x, -128
  %c7 = icmp sle i8 %x, %y
  %r7 = and i1 %m7, %c7   ; (X == MIN) && (X <= Y) --> X == MIN

  %m8 = icmp ne i8 %x, -128
  %c8 = icmp sgt i8 %x, %y
  %r8 = or i1 %m8, %c8   ; (X != MIN) || (X > Y) --> X != MIN

  %m9 = icmp ne i8 %x, 127
  %c9 = icmp slt i8 %x, %y
  %r9 = and i1 %m9, %c9    ; (X != MAX) && (X < Y) --> X < Y

  %m10 = icmp eq i8 %x, 127
  %c10 = icmp sge i8 %x, %y
  %r10 = or i1 %m10, %c10    ; (X == MAX) || (X >= Y) --> X >= Y

  %m11 = icmp ne i8 %x, -128
  %c11 = icmp sgt i8 %x, %y
  %r11 = and i1 %m11, %c11    ; (X != MIN) && (X > Y) --> X > Y

  %m12 = icmp eq i8 %x, -128
  %c12 = icmp sle i8 %x, %y
  %r12 = or i1 %m12, %c12    ; (X == MIN) || (X <= Y) --> X <= Y

  call void @use(i1 %r1, i1 %r2, i1 %r3, i1 %r4, i1 %r5, i1 %r6, i1 %r7, i1 %r8, i1 %r9, i1 %r10, i1 %r11, i1 %r12)
  ret void
}

define void @tgt(i8 %x, i8 %y)  {
  %m5 = icmp eq i8 %x, 127
  %m6 = icmp ne i8 %x, 127
  %m7 = icmp eq i8 %x, -128
  %m8 = icmp ne i8 %x, -128
  %c9 = icmp slt i8 %x, %y
  %c10 = icmp sge i8 %x, %y
  %c11 = icmp sgt i8 %x, %y
  %c12 = icmp sle i8 %x, %y
  call void @use(i1 0, i1 1, i1 0, i1 1, i1 %m5, i1 %m6, i1 %m7, i1 %m8, i1 %c9, i1 %c10, i1 %c11, i1 %c12)
  ret void
}

Differential Revision: https://reviews.llvm.org/D78430