[all-commits] [llvm/llvm-project] 04e45a: [InstSimplify] fold nested min/max intrinsics with...

[RotateRight via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: 04e45ae1c6d2fdbf3fd4242df69d1511df757d48
      https://github.com/llvm/llvm-project/commit/04e45ae1c6d2fdbf3fd4242df69d1511df757d48
  Author: Sanjay Patel <spatel at rotateright.com>
  Date:   2020-08-04 (Tue, 04 Aug 2020)

  Changed paths:
    M llvm/lib/Analysis/InstructionSimplify.cpp
    M llvm/test/Transforms/InstSimplify/maxmin_intrinsics.ll

  Log Message:
  -----------
  [InstSimplify] fold nested min/max intrinsics with constant operands

This is based on the existing code for the non-intrinsic idioms
in InstCombine.

The vector constant constraint is non-obvious: undefs should be
ok in the outer call, but they can't propagate safely from the
inner call in all cases. Example:

https://alive2.llvm.org/ce/z/-2bVbM
  define <2 x i8> @src(<2 x i8> %x) {
  %0:
    %m = umin <2 x i8> %x, { 7, undef }
    %m2 = umin <2 x i8> { 9, 9 }, %m
    ret <2 x i8> %m2
  }
  =>
  define <2 x i8> @tgt(<2 x i8> %x) {
  %0:
    %m = umin <2 x i8> %x, { 7, undef }
    ret <2 x i8> %m
  }
  Transformation doesn't verify!
  ERROR: Value mismatch

  Example:
  <2 x i8> %x = < undef, undef >

  Source:
  <2 x i8> %m = < #x00 (0)	[based on undef value], #x00 (0) >
  <2 x i8> %m2 = < #x00 (0), #x00 (0) >

  Target:
  <2 x i8> %m = < #x07 (7), #x10 (16) >
  Source value: < #x00 (0), #x00 (0) >
  Target value: < #x07 (7), #x10 (16) >