[PATCH] D149423: [ValueTracking] Use knownbits interface for determining if `div`/`rem` are safe to speculate

[Alexander Kornienko via Phabricator via llvm-commits]

alexfh added a comment.

  $ clang-6cdc229a64be8dacba40d30a9032c14f51ee30c0 -fsanitize=memory -O2 q.cc -S -emit-llvm -o good.ll
  $ clang-6c667abf3294d61e4fbe1238e1755c79f7547f1b -fsanitize=memory -O2 q.cc -S -emit-llvm -o bad.ll
  $ diff -u good.ll bad.ll
  --- good.ll
  +++ bad.ll
  @@ -11,8 +11,10 @@
     %call = tail call noundef i32 @_Z1qv()
     %spec.store.select = tail call i32 @llvm.umax.i32(i32 %call, i32 1)
     %1 = icmp ugt i32 %spec.store.select, 8192
  -  %div = udiv i32 8192, %spec.store.select
  -  %spec.store.select4 = select i1 %1, i32 1, i32 %div
  +  %div.rhs.trunc = trunc i32 %spec.store.select to i16
  +  %div7 = udiv i16 8192, %div.rhs.trunc
  +  %div.zext = zext i16 %div7 to i32
  +  %spec.store.select4 = select i1 %1, i32 1, i32 %div.zext
     ret i32 %spec.store.select4
   }
   
  @@ -40,4 +42,4 @@
   
   !0 = !{i32 1, !"wchar_size", i32 4}
   !1 = !{i32 7, !"uwtable", i32 2}
  -!2 = !{!"clang version trunk (6cdc229a64be8dacba40d30a9032c14f51ee30c0)"}
  +!2 = !{!"clang version trunk (6c667abf3294d61e4fbe1238e1755c79f7547f1b)"}


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D149423/new/

https://reviews.llvm.org/D149423