[llvm] 5cbb265 - [GVN] Fold equivalent freeze instructions

[Juneyoung Lee via llvm-commits]

Author: Juneyoung Lee
Date: 2020-03-01T07:32:05+09:00
New Revision: 5cbb26569474f33a39942255ba96f3427c155087

URL: https://github.com/llvm/llvm-project/commit/5cbb26569474f33a39942255ba96f3427c155087
DIFF: https://github.com/llvm/llvm-project/commit/5cbb26569474f33a39942255ba96f3427c155087.diff

LOG: [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

Added: 
    llvm/test/Transforms/GVN/freeze.ll

Modified: 
    llvm/lib/Transforms/Scalar/GVN.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/Scalar/GVN.cpp b/llvm/lib/Transforms/Scalar/GVN.cpp
index abdf5ecc88d6..6b9792aa77b0 100644
--- a/llvm/lib/Transforms/Scalar/GVN.cpp
+++ b/llvm/lib/Transforms/Scalar/GVN.cpp
@@ -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:

diff  --git a/llvm/test/Transforms/GVN/freeze.ll b/llvm/test/Transforms/GVN/freeze.ll
new file mode 100644
index 000000000000..1a6d84b5f139
--- /dev/null
+++ b/llvm/test/Transforms/GVN/freeze.ll
@@ -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)
+