allow branch weight metadata on select instructions (PR26636)
As noted in:
https://llvm.org/bugs/show_bug.cgi?id=26636
This doesn't accomplish anything on its own. It's the first step towards preserving
and using branch weights with selects.
The next step would be to make sure we're propagating the info in all of the other
places where we create selects (SimplifyCFG, InstCombine, etc). I don't think there's
an easy fix to make this happen; we have to look at each transform individually to
determine how to correctly propagate the weights.
Along with that step, we need to then use the weights when making subsequent transform
decisions such as discussed in http://reviews.llvm.org/D16836.
The inliner test is independent but closely related. It verifies that metadata is
preserved when both branches and selects are cloned.
Differential Revision: http://reviews.llvm.org/D18133
llvm-svn: 263482
diff --git a/llvm/include/llvm/IR/IRBuilder.h b/llvm/include/llvm/IR/IRBuilder.h
index c6c12fa..a9c9c81 100644
--- a/llvm/include/llvm/IR/IRBuilder.h
+++ b/llvm/include/llvm/IR/IRBuilder.h
@@ -1569,12 +1569,16 @@
}
Value *CreateSelect(Value *C, Value *True, Value *False,
- const Twine &Name = "") {
+ const Twine &Name = "", MDNode *ProfWeights = nullptr) {
if (Constant *CC = dyn_cast<Constant>(C))
if (Constant *TC = dyn_cast<Constant>(True))
if (Constant *FC = dyn_cast<Constant>(False))
return Insert(Folder.CreateSelect(CC, TC, FC), Name);
- return Insert(SelectInst::Create(C, True, False), Name);
+
+ SelectInst *Sel = SelectInst::Create(C, True, False);
+ // TODO: "unpredictable" metadata can apply to a select too.
+ Sel->setMetadata(LLVMContext::MD_prof, ProfWeights);
+ return Insert(Sel, Name);
}
VAArgInst *CreateVAArg(Value *List, Type *Ty, const Twine &Name = "") {
diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index b08fb04..bf94e26 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -1935,7 +1935,8 @@
Value *TrueVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
Value *FalseVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
- Value *Select = Builder.CreateSelect(IfCond, TrueVal, FalseVal);
+ MDNode *MDN = InsertPt->getMetadata(LLVMContext::MD_prof);
+ Value *Select = Builder.CreateSelect(IfCond, TrueVal, FalseVal, "", MDN);
PN->replaceAllUsesWith(Select);
Select->takeName(PN);
PN->eraseFromParent();
diff --git a/llvm/test/Transforms/Inline/profile-meta.ll b/llvm/test/Transforms/Inline/profile-meta.ll
new file mode 100644
index 0000000..5000b83
--- /dev/null
+++ b/llvm/test/Transforms/Inline/profile-meta.ll
@@ -0,0 +1,41 @@
+; RUN: opt < %s -S -inline | FileCheck %s
+
+; Make sure that profile metadata is preserved when cloning a select.
+
+define i32 @callee_with_select(i1 %c, i32 %a, i32 %b) {
+ %sel = select i1 %c, i32 %a, i32 %b, !prof !0
+ ret i32 %sel
+}
+
+define i32 @caller_of_select(i1 %C, i32 %A, i32 %B) {
+ %ret = call i32 @callee_with_select(i1 %C, i32 %A, i32 %B)
+ ret i32 %ret
+
+; CHECK-LABEL: @caller_of_select(
+; CHECK-NEXT: [[SEL:%.*]] = select i1 %C, i32 %A, i32 %B, !prof !0
+; CHECK-NEXT: ret i32 [[SEL]]
+}
+
+; Make sure that profile metadata is preserved when cloning a branch.
+
+define i32 @callee_with_branch(i1 %c) {
+ br i1 %c, label %if, label %else, !prof !1
+if:
+ ret i32 1
+else:
+ ret i32 2
+}
+
+define i32 @caller_of_branch(i1 %C) {
+ %ret = call i32 @callee_with_branch(i1 %C)
+ ret i32 %ret
+
+; CHECK-LABEL: @caller_of_branch(
+; CHECK-NEXT: br i1 %C, label %{{.*}}, label %{{.*}}, !prof !1
+}
+
+!0 = !{!"branch_weights", i32 1, i32 2}
+!1 = !{!"branch_weights", i32 3, i32 4}
+; CHECK: !0 = !{!"branch_weights", i32 1, i32 2}
+; CHECK: !1 = !{!"branch_weights", i32 3, i32 4}
+
diff --git a/llvm/test/Transforms/SimplifyCFG/PhiEliminate2.ll b/llvm/test/Transforms/SimplifyCFG/PhiEliminate2.ll
index fcda12c..60931fc7 100644
--- a/llvm/test/Transforms/SimplifyCFG/PhiEliminate2.ll
+++ b/llvm/test/Transforms/SimplifyCFG/PhiEliminate2.ll
@@ -1,8 +1,11 @@
; RUN: opt < %s -simplifycfg -S | FileCheck %s
+; Use a select to make this a single BB.
+; Also, make sure the profile metadata is propagated to the select (PR26636).
+
define i32 @FoldTwoEntryPHINode(i1 %C, i32 %V1, i32 %V2, i16 %V3) {
entry:
- br i1 %C, label %then, label %else
+ br i1 %C, label %then, label %else, !prof !0
then:
%V4 = or i32 %V2, %V1
br label %Cont
@@ -18,8 +21,12 @@
; CHECK-NEXT: entry:
; CHECK-NEXT: %V5 = sext i16 %V3 to i32
; CHECK-NEXT: %V4 = or i32 %V2, %V1
-; CHECK-NEXT: %V6 = select i1 %C, i32 %V4, i32 %V5
+; CHECK-NEXT: %V6 = select i1 %C, i32 %V4, i32 %V5, !prof !0
; CHECK-NEXT: %0 = call i32 @FoldTwoEntryPHINode(i1 false, i32 0, i32 0, i16 0)
; CHECK-NEXT: ret i32 %V1
}
+!0 = !{!"branch_weights", i32 3, i32 5}
+
+; CHECK: !0 = !{!"branch_weights", i32 3, i32 5}
+