[PATCH] D85446: [InstCombine] Add vector support to mul(add(x,c),negpow2) -> mul(sub(-c,x),pow2) folds

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri added inline comments.


================
Comment at: llvm/test/Transforms/InstCombine/mul.ll:976
 ; CHECK-LABEL: @muladd2_vec(
-; CHECK-NEXT:    [[TMP1:%.*]] = mul <2 x i32> [[A0:%.*]], <i32 -4, i32 -4>
-; CHECK-NEXT:    [[MUL:%.*]] = add <2 x i32> [[TMP1]], <i32 -64, i32 -64>
+; CHECK-NEXT:    [[SUBC_NEG:%.*]] = mul <2 x i32> [[A0:%.*]], <i32 -4, i32 -4>
+; CHECK-NEXT:    [[MUL:%.*]] = add <2 x i32> [[SUBC_NEG]], <i32 -64, i32 -64>
----------------
lebedev.ri wrote:
> And another example that we need something like Negator-driven hoisting.
Also, there's some very interesting fold pirouetting going on there.
I will be surprised if we won't encounter conflicting transforms here soon.

```
INSTCOMBINE ITERATION #1 on muladd2
IC: ADD:   ret i32 %mul
IC: ADD:   %mul = mul i32 %add, -4
IC: ADD:   %add = add i32 %a0, 16
IC: Visiting:   %add = add i32 %a0, 16
IC: Visiting:   %mul = mul i32 %add, -4
Negator: attempting to sink negation into   %add = add i32 %a0, 16
Negator: successfully sunk negation into   %add = add i32 %a0, 16
         NEW:   %add.neg = sub i32 -16, %a0
Negator: Propagating 1 instrs to InstCombine
IC: ADD DEFERRED:   %add.neg = sub i32 -16, %a0
IC: Old =   %mul = mul i32 %add, -4
    New =   %mul = mul i32 %add.neg, 4
IC: ADD:   %mul = mul i32 %add.neg, 4
IC: ERASE   %1 = mul i32 %add, -4
IC: ADD DEFERRED:   %add = add i32 %a0, 16
IC: ERASE   %add = add i32 %a0, 16
IC: ADD:   %add.neg = sub i32 -16, %a0
IC: Visiting:   %add.neg = sub i32 -16, %a0
Negator: attempting to sink negation into i32 %a0
Negator: failed to sink negation into i32 %a0
IC: Visiting:   %mul = mul i32 %add.neg, 4
IC: Old =   %mul = mul i32 %add.neg, 4
    New =   <badref> = shl i32 %add.neg, 2
IC: ADD:   %mul = shl i32 %add.neg, 2
IC: ERASE   %1 = mul i32 %add.neg, 4
IC: ADD DEFERRED:   %add.neg = sub i32 -16, %a0
IC: ADD:   %add.neg = sub i32 -16, %a0
IC: Visiting:   %add.neg = sub i32 -16, %a0
Negator: attempting to sink negation into i32 %a0
Negator: failed to sink negation into i32 %a0
IC: Visiting:   %mul = shl i32 %add.neg, 2
IC: ADD DEFERRED:   %add.neg = sub i32 1073741808, %a0
IC: Mod =   %mul = shl i32 %add.neg, 2
    New =   %mul = shl i32 %add.neg, 2
IC: ADD:   %mul = shl i32 %add.neg, 2
IC: ADD:   %add.neg = sub i32 1073741808, %a0
IC: Visiting:   %add.neg = sub i32 1073741808, %a0
Negator: attempting to sink negation into i32 %a0
Negator: failed to sink negation into i32 %a0
IC: Visiting:   %mul = shl i32 %add.neg, 2
IC: ADD DEFERRED:   %1 = shl i32 %a0, 2
IC: Old =   %mul = shl i32 %1, 2
    New =   <badref> = sub i32 -64, %add.neg
IC: ADD:   %mul = sub i32 -64, %add.neg
IC: ERASE   %2 = shl i32 %1, 2
IC: ADD DEFERRED:   %1 = sub i32 1073741808, %a0
IC: ERASE   %1 = sub i32 1073741808, %a0
IC: ADD:   %add.neg = shl i32 %a0, 2
IC: Visiting:   %add.neg = shl i32 %a0, 2
IC: Visiting:   %mul = sub i32 -64, %add.neg
Negator: attempting to sink negation into   %add.neg = shl i32 %a0, 2
Negator: successfully sunk negation into   %add.neg = shl i32 %a0, 2
         NEW:   %add.neg.neg = mul i32 %a0, -4
Negator: Propagating 1 instrs to InstCombine
IC: ADD DEFERRED:   %add.neg.neg = mul i32 %a0, -4
IC: Old =   %mul = sub i32 -64, %add.neg
    New =   <badref> = add i32 %add.neg.neg, -64
IC: ADD:   %mul = add i32 %add.neg.neg, -64
IC: ERASE   %1 = sub i32 -64, %add.neg
IC: ADD DEFERRED:   %add.neg = shl i32 %a0, 2
IC: ERASE   %add.neg = shl i32 %a0, 2
IC: ADD:   %add.neg.neg = mul i32 %a0, -4
IC: Visiting:   %add.neg.neg = mul i32 %a0, -4
Negator: attempting to sink negation into i32 %a0
Negator: failed to sink negation into i32 %a0
IC: Visiting:   %mul = add i32 %add.neg.neg, -64
IC: Visiting:   ret i32 %mul


INSTCOMBINE ITERATION #2 on muladd2
IC: ADD:   ret i32 %mul
IC: ADD:   %mul = add i32 %add.neg.neg, -64
IC: ADD:   %add.neg.neg = mul i32 %a0, -4
IC: Visiting:   %add.neg.neg = mul i32 %a0, -4
Negator: attempting to sink negation into i32 %a0
Negator: failed to sink negation into i32 %a0
IC: Visiting:   %mul = add i32 %add.neg.neg, -64
IC: Visiting:   ret i32 %mul

```


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D85446/new/

https://reviews.llvm.org/D85446