[InstCombine] canonicalize more unsigned saturated add with 'not'

Yet another pattern variation suggested by:
https://bugs.llvm.org/show_bug.cgi?id=14613

There are 8 more potential commuted patterns here on top of the
8 that were already handled (rL354221, rL354276, rL354393).
We have the obvious commute of the 'add' + commute of the cmp
predicate/operands (ugt/ult) + commute of the select operands:

Name: base
%notx = xor i32 %x, -1
%a = add i32 %notx, %y
%c = icmp ult i32 %x, %y
%r = select i1 %c, i32 -1, i32 %a
=>
%c2 = icmp ult i32 %a, %y
%r = select i1 %c2, i32 -1, i32 %a

Name: ugt
%notx = xor i32 %x, -1
%a = add i32 %notx, %y
%c = icmp ugt i32 %y, %x
%r = select i1 %c, i32 -1, i32 %a
=>
%c2 = icmp ult i32 %a, %y
%r = select i1 %c2, i32 -1, i32 %a

Name: commute select
%notx = xor i32 %x, -1
%a = add i32 %notx, %y
%c = icmp ult i32 %y, %x
%r = select i1 %c, i32 %a, i32 -1
=>
%c2 = icmp ult i32 %a, %y
%r = select i1 %c2, i32 -1, i32 %a

Name: ugt + commute select
%notx = xor i32 %x, -1
%a = add i32 %notx, %y
%c = icmp ugt i32 %x, %y
%r = select i1 %c, i32 %a, i32 -1
=>
%c2 = icmp ult i32 %a, %y
%r = select i1 %c2, i32 -1, i32 %a

https://rise4fun.com/Alive/den

llvm-svn: 354887

1 files changed, 11 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
index d153c848d38..79835ef9316 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -725,6 +725,17 @@ static Value *canonicalizeSaturatedAdd(ICmpInst *Cmp, Value *TVal, Value *FVal,
     Value *NewCmp = Builder.CreateICmp(ICmpInst::ICMP_ULT, FVal, Y);
     return Builder.CreateSelect(NewCmp, TVal, FVal);
   }
+  // The 'not' op may be included in the sum but not the compare.
+  X = Cmp0;
+  Y = Cmp1;
+  if (match(FVal, m_c_Add(m_Not(m_Specific(X)), m_Specific(Y)))) {
+    // Change the comparison to use the sum (false value of the select). That is
+    // a canonical pattern match form for uadd.with.overflow:
+    // (X u< Y) ? -1 : (~X + Y) --> ((~X + Y) u< Y) ? -1 : (~X + Y)
+    // (X u< Y) ? -1 : (Y + ~X) --> ((Y + ~X) u< Y) ? -1 : (Y + ~X)
+    Value *NewCmp = Builder.CreateICmp(ICmpInst::ICMP_ULT, FVal, Y);
+    return Builder.CreateSelect(NewCmp, TVal, FVal);
+  }
 
   return nullptr;
 }