[PATCH] D141180: [X86] Only match BMI (BLSR, BLSI, BLSMSK) if the add/sub op is single use

[Noah Goldstein via Phabricator via llvm-commits]

goldstein.w.n added inline comments.


================
Comment at: llvm/lib/Target/X86/X86InstrInfo.td:1272
 
+// An 'ineg' node with a single use.
+def ineg_su : PatFrag<(ops node:$v), (ineg node:$v), [{
----------------
craig.topper wrote:
> Maybe we should have
> 
> ```
> `class binop_oneuse<SDPatternOperator operator>
>     : PatFrag<(ops node:$A, node:$B),
>               (operator node:$A, node:$B), [{
>   return N->hasOneUse();
> }]>;`
> 
> def add_su : binop_oneuse<add>;
> def and_su : binop_oneuse<and>;
> def srl_su : binop_oneuse<srl>;
> 
> class unop_oneuse<SDPatternOperator operator>
>     : PatFrag<(ops node:$A),
>               (operator node:$A), [{
>   return N->hasOneUse();
> }]>;
> 
> def ineg_su : unop_oneuse<ineg>;
> def trunc_su : unop_oneuse<trunc>;
> ```
> Maybe we should have
> 
> ```
> `class binop_oneuse<SDPatternOperator operator>
>     : PatFrag<(ops node:$A, node:$B),
>               (operator node:$A, node:$B), [{
>   return N->hasOneUse();
> }]>;`
> 
> def add_su : binop_oneuse<add>;
> def and_su : binop_oneuse<and>;
> def srl_su : binop_oneuse<srl>;
> 
> class unop_oneuse<SDPatternOperator operator>
>     : PatFrag<(ops node:$A),
>               (operator node:$A), [{
>   return N->hasOneUse();
> }]>;
> 
> def ineg_su : unop_oneuse<ineg>;
> def trunc_su : unop_oneuse<trunc>;
> ```

Makes sense, will do for V2.

Any thoughts on:
"""
Note, this may cause more mov instructions to be emitted sometimes
because BMI instructions only have 1 src and write-only to dst. A
better approach may be to only avoid BMI for (and/xor X, (add/sub
0/-1, X)) if this is the last use of X but NOT the last use of
(add/sub 0/-1, X).
"""
?


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https://reviews.llvm.org/D141180