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Add a routine to swap branch instruction operands, and update any

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profile metadata at the same time. Use it to preserve metadata attached
to a branch when re-writing it in InstCombine.

Add metadata to the canonicalize_branch InstCombine test, and check that
it is tranformed correctly.

Reviewed by Nick Lewycky!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@142168 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chandler Carruth 2011-10-17 01:11:57 +00:00
parent 1416dc29d8
commit 602650c988
4 changed files with 59 additions and 9 deletions
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7
include/llvm/Instructions.h
View File

@ -2367,6 +2367,13 @@ public:
*(&Op<-1>() - idx) = (Value*)NewSucc;
}
/// \brief Swap the successors of this branch instruction.
///
/// Swaps the successors of the branch instruction. This also swaps any
/// branch weight metadata associated with the instruction so that it
/// continues to map correctly to each operand.
void swapSuccessors();
// Methods for support type inquiry through isa, cast, and dyn_cast:
static inline bool classof(const BranchInst *) { return true; }
static inline bool classof(const Instruction *I) {

9
lib/Transforms/InstCombine/InstructionCombining.cpp
View File

@ -1190,8 +1190,7 @@ Instruction *InstCombiner::visitBranchInst(BranchInst &BI) {
!isa<Constant>(X)) {
// Swap Destinations and condition...
BI.setCondition(X);
BI.setSuccessor(0, FalseDest);
BI.setSuccessor(1, TrueDest);
BI.swapSuccessors();
return &BI;
}
@ -1206,8 +1205,7 @@ Instruction *InstCombiner::visitBranchInst(BranchInst &BI) {
Cond->setPredicate(FCmpInst::getInversePredicate(FPred));
// Swap Destinations and condition.
BI.setSuccessor(0, FalseDest);
BI.setSuccessor(1, TrueDest);
BI.swapSuccessors();
Worklist.Add(Cond);
return &BI;
}
@ -1223,8 +1221,7 @@ Instruction *InstCombiner::visitBranchInst(BranchInst &BI) {
ICmpInst *Cond = cast<ICmpInst>(BI.getCondition());
Cond->setPredicate(ICmpInst::getInversePredicate(IPred));
// Swap Destinations and condition.
BI.setSuccessor(0, FalseDest);
BI.setSuccessor(1, TrueDest);
BI.swapSuccessors();
Worklist.Add(Cond);
return &BI;
}

21
lib/VMCore/Instructions.cpp
View File

@ -785,6 +785,27 @@ BranchInst::BranchInst(const BranchInst &BI) :
SubclassOptionalData = BI.SubclassOptionalData;
}
void BranchInst::swapSuccessors() {
assert(isConditional() &&
"Cannot swap successors of an unconditional branch");
Op<-1>().swap(Op<-2>());
// Update profile metadata if present and it matches our structural
// expectations.
MDNode *ProfileData = getMetadata(LLVMContext::MD_prof);
if (!ProfileData || ProfileData->getNumOperands() != 3)
return;
// The first operand is the name. Fetch them backwards and build a new one.
Value *Ops[] = {
ProfileData->getOperand(0),
ProfileData->getOperand(2),
ProfileData->getOperand(1)
};
setMetadata(LLVMContext::MD_prof,
MDNode::get(ProfileData->getContext(), Ops));
}
BasicBlock *BranchInst::getSuccessorV(unsigned idx) const {
return getSuccessor(idx);
}

31
test/Transforms/InstCombine/canonicalize_branch.ll
View File

@ -1,8 +1,23 @@
; RUN: opt < %s -instcombine -S | FileCheck %s
; Test an already canonical branch to make sure we don't flip those.
define i32 @test0(i32 %X, i32 %Y) {
%C = icmp eq i32 %X, %Y
br i1 %C, label %T, label %F, !prof !0
; CHECK: @test0
; CHECK: %C = icmp eq i32 %X, %Y
; CHECK: br i1 %C, label %T, label %F
T:
ret i32 12
F:
ret i32 123
}
define i32 @test1(i32 %X, i32 %Y) {
%C = icmp ne i32 %X, %Y
br i1 %C, label %T, label %F
br i1 %C, label %T, label %F, !prof !1
; CHECK: @test1
; CHECK: %C = icmp eq i32 %X, %Y
@ -16,7 +31,7 @@ F:
define i32 @test2(i32 %X, i32 %Y) {
%C = icmp ule i32 %X, %Y
br i1 %C, label %T, label %F
br i1 %C, label %T, label %F, !prof !2
; CHECK: @test2
; CHECK: %C = icmp ugt i32 %X, %Y
@ -30,7 +45,7 @@ F:
define i32 @test3(i32 %X, i32 %Y) {
%C = icmp uge i32 %X, %Y
br i1 %C, label %T, label %F
br i1 %C, label %T, label %F, !prof !3
; CHECK: @test3
; CHECK: %C = icmp ult i32 %X, %Y
@ -42,3 +57,13 @@ F:
ret i32 123
}
!0 = metadata !{metadata !"branch_weights", i32 1, i32 2}
!1 = metadata !{metadata !"branch_weights", i32 3, i32 4}
!2 = metadata !{metadata !"branch_weights", i32 5, i32 6}
!3 = metadata !{metadata !"branch_weights", i32 7, i32 8}
; Base case shouldn't change.
; CHECK: !0 = {{.*}} i32 1, i32 2}
; Ensure that the branch metadata is reversed to match the reversals above.
; CHECK: !1 = {{.*}} i32 4, i32 3}
; CHECK: !2 = {{.*}} i32 6, i32 5}
; CHECK: !3 = {{.*}} i32 8, i32 7}