Commit 5cbb2656 authored by Juneyoung Lee's avatar Juneyoung Lee
Browse files

[GVN] Fold equivalent freeze instructions 

Summary:
This patch defines two freeze instructions to have the same value number if they are equivalent.

This is allowed because GVN replaces all uses of a duplicated instruction with another.

If it partially rewrites use, it is not allowed. e.g)

```
a = freeze(x)
b = freeze(x)
use(a)
use(a)
use(b)
=>
use(a)
use(b) // This is not allowed!
use(b)
```

Reviewers: fhahn, reames, spatel, efriedma

Reviewed By: fhahn

Subscribers: lebedev.ri, hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D75398
parent 5d6dfd87

llvm/lib/Transforms/Scalar/GVN.cpp

+1 −0
Original line number Diff line number Diff line
@@ -531,6 +531,7 @@ uint32_t GVN::ValueTable::lookupOrAdd(Value *V) { 
    case Instruction::AddrSpaceCast:

    case Instruction::BitCast:

    case Instruction::Select:

    case Instruction::Freeze:

    case Instruction::ExtractElement:

    case Instruction::InsertElement:

    case Instruction::ShuffleVector:

llvm/test/Transforms/GVN/freeze.ll

0 → 100644
+56 −0
Original line number Diff line number Diff line 
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py

; RUN: opt < %s -gvn -S | FileCheck %s

; RUN: opt < %s -passes=gvn -S | FileCheck %s



define i1 @f(i1 %a) {

; CHECK-LABEL: @f(

; CHECK-NEXT:    [[B:%.*]] = freeze i1 [[A:%.*]]

; CHECK-NEXT:    ret i1 [[B]]

;

  %b = freeze i1 %a

  %c = freeze i1 %a

  %d = and i1 %b, %b

  ret i1 %d

}



define void @f_multipleuses(i1 %a) {

; CHECK-LABEL: @f_multipleuses(

; CHECK-NEXT:    [[B:%.*]] = freeze i1 [[A:%.*]]

; CHECK-NEXT:    call void @use1(i1 [[B]])

; CHECK-NEXT:    call void @use1(i1 [[B]])

; CHECK-NEXT:    call void @use1(i1 [[B]])

; CHECK-NEXT:    ret void

;

  %b = freeze i1 %a

  %c = freeze i1 %a

  call void @use1(i1 %b)

  call void @use1(i1 %c)

  call void @use1(i1 %c)

  ret void

}



define void @f_dom(i1 %cond, i1 %a) {

; CHECK-LABEL: @f_dom(

; CHECK-NEXT:    br i1 [[COND:%.*]], label [[BB1:%.*]], label [[BB2:%.*]]

; CHECK:       BB1:

; CHECK-NEXT:    [[X:%.*]] = freeze i1 [[A:%.*]]

; CHECK-NEXT:    call void @use1(i1 [[X]])

; CHECK-NEXT:    ret void

; CHECK:       BB2:

; CHECK-NEXT:    [[Y:%.*]] = freeze i1 [[A]]

; CHECK-NEXT:    call void @use2(i1 [[Y]])

; CHECK-NEXT:    ret void

;

  br i1 %cond, label %BB1, label %BB2

BB1:

  %x = freeze i1 %a

  call void @use1(i1 %x)

  ret void

BB2:

  %y = freeze i1 %a

  call void @use2(i1 %y) ; cannot use %x

  ret void

}

declare void @use1(i1)

declare void @use2(i1)