[llvm] [InstCombinePHI] Enhance PHI CSE to remove redundant phis (PR #163453)

[Yingwei Zheng via llvm-commits]

dtcxzyw wrote:

> target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
> target triple = "x86_64-unknown-fuchsia"
> 
> define i8 @f(ptr %__p, i1 %0) {
> entry:
>   br label %for.cond
> 
> for.cond:                                         ; preds = %for.inc, %entry
>   %__p.pn = phi ptr [ %__p, %entry ], [ %__p.addr.0, %for.inc ]
>   %__p.addr.0 = getelementptr i8, ptr %__p.pn, i64 1
>   br i1 false, label %cleanup17, label %for.body
> 
> for.body:                                         ; preds = %for.cond
>   %1 = load i8, ptr %__p.pn, align 1
>   br i1 false, label %for.inc, label %if.else
> 
> if.else:                                          ; preds = %for.body
>   %incdec.ptr11 = getelementptr i8, ptr %__p.pn, i64 2
>   %spec.select = select i1 %0, ptr %__p.addr.0, ptr %incdec.ptr11
>   br label %cleanup17
> 
> for.inc:                                          ; preds = %for.body
>   br label %for.cond
> 
> cleanup17:                                        ; preds = %if.else, %for.cond
>   %__p.addr.3 = phi ptr [ %spec.select, %if.else ], [ %__p.addr.0, %for.cond ]
>   %2 = load i8, ptr %__p.addr.3, align 1
>   ret i8 %2
> }

> PN = %lsr.iv = phi ptr [ %scevgep1, %for.inc ], [ %scevgep, %entry ]
  IdenticalPN = %sunk_phi5 = phi ptr

It is caused by CGP:AddressingModeMatcher. It calls simplifyInstruction before filling the incoming values of new PHI nodes.
I will post a fix tonight (UTC+8).


https://github.com/llvm/llvm-project/pull/163453