Introducing llvm.invariant.group.barrier intrinsic

For more info for what reason it was invented, goto:
http://lists.llvm.org/pipermail/cfe-dev/2015-July/044227.html

invariant.group.barrier:
http://reviews.llvm.org/D12310
docs:
http://reviews.llvm.org/D11399
CodeGenPrepare:
http://reviews.llvm.org/D12875

llvm-svn: 247711

1 files changed, 79 insertions, 0 deletions

diff --git a/llvm/test/Transforms/GlobalOpt/invariant.group.barrier.ll b/llvm/test/Transforms/GlobalOpt/invariant.group.barrier.ll
new file mode 100644
index 00000000000..54d91d40801
--- /dev/null
+++ b/llvm/test/Transforms/GlobalOpt/invariant.group.barrier.ll
@@ -0,0 +1,79 @@
+; RUN: opt -S -globalopt < %s | FileCheck %s
+
+; This test is hint, what could globalOpt optimize and what it can't
+; FIXME: @tmp and @tmp2 can be safely set to 42
+; CHECK: @tmp = global i32 0
+; CHECK: @tmp2 = global i32 0
+; CHECK: @tmp3 = global i32 0
+
+@tmp = global i32 0
+@tmp2 = global i32 0
+@tmp3 = global i32 0
+@ptrToTmp3 = global i32* null
+
+@llvm.global_ctors = appending global [1 x { i32, void ()* }] [{ i32, void ()* } { i32 65535, void ()* @_GLOBAL__I_a }]
+
+define i32 @TheAnswerToLifeTheUniverseAndEverything() {
+  ret i32 42
+}
+
+define void @_GLOBAL__I_a() {
+enter:
+  call void @_optimizable()
+  call void @_not_optimizable()
+  ret void
+}
+
+define void @_optimizable() {
+enter:
+  %valptr = alloca i32
+  
+  %val = call i32 @TheAnswerToLifeTheUniverseAndEverything()
+  store i32 %val, i32* @tmp
+  store i32 %val, i32* %valptr
+  
+  %0 = bitcast i32* %valptr to i8*
+  %barr = call i8* @llvm.invariant.group.barrier(i8* %0)
+  %1 = bitcast i8* %barr to i32*
+  
+  %val2 = load i32, i32* %1
+  store i32 %val2, i32* @tmp2
+  ret void
+}
+
+; We can't step through invariant.group.barrier here, because that would change
+; this load in @usage_of_globals()
+; val = load i32, i32* %ptrVal, !invariant.group !0 
+; into 
+; %val = load i32, i32* @tmp3, !invariant.group !0
+; and then we could assume that %val and %val2 to be the same, which coud be 
+; false, because @changeTmp3ValAndCallBarrierInside() may change the value
+; of @tmp3.
+define void @_not_optimizable() {
+enter:
+  store i32 13, i32* @tmp3, !invariant.group !0
+  
+  %0 = bitcast i32* @tmp3 to i8*
+  %barr = call i8* @llvm.invariant.group.barrier(i8* %0)
+  %1 = bitcast i8* %barr to i32*
+  
+  store i32* %1, i32** @ptrToTmp3
+  store i32 42, i32* %1, !invariant.group !0
+  
+  ret void
+}
+define void @usage_of_globals() {
+entry:
+  %ptrVal = load i32*, i32** @ptrToTmp3
+  %val = load i32, i32* %ptrVal, !invariant.group !0
+  
+  call void @changeTmp3ValAndCallBarrierInside()
+  %val2 = load i32, i32* @tmp3, !invariant.group !0
+  ret void;
+}
+
+declare void @changeTmp3ValAndCallBarrierInside()
+
+declare i8* @llvm.invariant.group.barrier(i8*)
+
+!0 = !{!"something"}