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Add check for "branch_weights" with prof metadata 

While we're here, fix the comment and variable names to make it
clear that these are raw weights, not percentages.

llvm-svn: 267491
This commit is contained in:
Sanjay Patel 2016-04-25 23:15:16 +00:00
parent ed737d7881
commit 82059090d3
3 changed files with 35 additions and 6 deletions
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7
llvm/include/llvm/IR/Instructions.h
View File

@ -2906,9 +2906,10 @@ public:
/// continues to map correctly to each operand.
void swapSuccessors();
/// Retrieve the probabilities of a conditional branch. Returns true on
/// success, or returns false if no or invalid metadata was found.
bool extractProfMetadata(uint64_t &ProbTrue, uint64_t &ProbFalse);
/// Retrieve the raw weight values of a conditional branch.
/// Returns true on success with profile weights filled in.
/// Returns false if no metadata or invalid metadata was found.
bool extractProfMetadata(uint64_t &TrueVal, uint64_t &FalseVal);
// Methods for support type inquiry through isa, cast, and dyn_cast:
static inline bool classof(const Instruction *I) {

10
llvm/lib/IR/Instructions.cpp
View File

@ -1120,20 +1120,24 @@ void BranchInst::swapSuccessors() {
MDNode::get(ProfileData->getContext(), Ops));
}
bool BranchInst::extractProfMetadata(uint64_t &ProbTrue, uint64_t &ProbFalse) {
bool BranchInst::extractProfMetadata(uint64_t &TrueVal, uint64_t &FalseVal) {
assert(isConditional() &&
"Looking for probabilities on unconditional branch?");
auto *ProfileData = getMetadata(LLVMContext::MD_prof);
if (!ProfileData || ProfileData->getNumOperands() != 3)
return false;
auto *ProfDataName = dyn_cast<MDString>(ProfileData->getOperand(0));
if (!ProfDataName || !ProfDataName->getString().equals("branch_weights"))
return false;
auto *CITrue = mdconst::dyn_extract<ConstantInt>(ProfileData->getOperand(1));
auto *CIFalse = mdconst::dyn_extract<ConstantInt>(ProfileData->getOperand(2));
if (!CITrue || !CIFalse)
return false;
ProbTrue = CITrue->getValue().getZExtValue();
ProbFalse = CIFalse->getValue().getZExtValue();
TrueVal = CITrue->getValue().getZExtValue();
FalseVal = CIFalse->getValue().getZExtValue();
return true;
}

24
llvm/test/Transforms/SimplifyCFG/preserve-branchweights.ll
View File

@ -21,6 +21,29 @@ Z:
ret void
}
; Make sure the metadata name string is "branch_weights" before propagating it.
define void @fake_weights(i1 %a, i1 %b) {
; CHECK-LABEL: @fake_weights(
entry:
br i1 %a, label %Y, label %X, !prof !12
; CHECK: %or.cond = and i1 %a.not, %c
; CHECK-NEXT: br i1 %or.cond, label %Z, label %Y
; CHECK-NOT: !prof !0
; CHECK: Y:
X:
%c = or i1 %b, false
br i1 %c, label %Z, label %Y, !prof !1
Y:
call void @helper(i32 0)
ret void
Z:
call void @helper(i32 1)
ret void
}
define void @test2(i1 %a, i1 %b) {
; CHECK-LABEL: @test2(
entry:
@ -376,6 +399,7 @@ for.exit:
!9 = !{!"branch_weights", i32 7, i32 6}
!10 = !{!"branch_weights", i32 672646, i32 21604207}
!11 = !{!"branch_weights", i32 6960, i32 21597248}
!12 = !{!"these_are_not_the_branch_weights_you_are_looking_for", i32 3, i32 5}
; CHECK: !0 = !{!"branch_weights", i32 5, i32 11}
; CHECK: !1 = !{!"branch_weights", i32 1, i32 5}