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[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
This commit is contained in:
Juneyoung Lee 2020-02-29 14:58:07 +09:00
parent 5d6dfd877f
commit 5cbb265694
2 changed files with 57 additions and 0 deletions
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1
llvm/lib/Transforms/Scalar/GVN.cpp
View File

@ -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:

56
llvm/test/Transforms/GVN/freeze.ll Normal file
View File

@ -0,0 +1,56 @@
; 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)