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[Bitcode] Drop invalid branch_weight in BitcodeReader 

Summary:
If bitcode reader gets an invalid branch weight, drop that from the
inputs. This allows us to read the broken modules we generated before
the verifier was able to catch this.

rdar://64870641

Reviewers: yrouban, t.p.northover, dexonsmith, arphaman, aprantl

Reviewed By: aprantl

Subscribers: aprantl, hiraditya, jkorous, ributzka, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D83699
This commit is contained in:
Steven Wu 2020-07-23 09:06:47 -07:00
parent 831ae45e3d
commit 78709345fb
3 changed files with 49 additions and 0 deletions
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30
llvm/lib/Bitcode/Reader/BitcodeReader.cpp
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@ -5394,6 +5394,36 @@ Error BitcodeReader::materialize(GlobalValue *GV) {
}
}
// "Upgrade" older incorrect branch weights by dropping them.
for (auto &I : instructions(F)) {
if (auto *MD = I.getMetadata(LLVMContext::MD_prof)) {
if (MD->getOperand(0) != nullptr && isa<MDString>(MD->getOperand(0))) {
MDString *MDS = cast<MDString>(MD->getOperand(0));
StringRef ProfName = MDS->getString();
// Check consistency of !prof branch_weights metadata.
if (!ProfName.equals("branch_weights"))
continue;
unsigned ExpectedNumOperands = 0;
if (BranchInst *BI = dyn_cast<BranchInst>(&I))
ExpectedNumOperands = BI->getNumSuccessors();
else if (SwitchInst *SI = dyn_cast<SwitchInst>(&I))
ExpectedNumOperands = SI->getNumSuccessors();
else if (isa<CallInst>(&I))
ExpectedNumOperands = 1;
else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(&I))
ExpectedNumOperands = IBI->getNumDestinations();
else if (isa<SelectInst>(&I))
ExpectedNumOperands = 2;
else
continue; // ignore and continue.
// If branch weight doesn't match, just strip branch weight.
if (MD->getNumOperands() != 1 + ExpectedNumOperands)
I.setMetadata(LLVMContext::MD_prof, nullptr);
}
}
}
// Look for functions that rely on old function attribute behavior.
UpgradeFunctionAttributes(*F);

BIN
llvm/test/Bitcode/Inputs/branch-weight.bc Normal file
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19
llvm/test/Bitcode/branch-weight.ll Normal file
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@ -0,0 +1,19 @@
;; Test strip branch_weight if operand number doesn't match.
;; Input bitcode is generated from:
;; define void @test(i1 %0) {
;; br i1 %0, label %2, label %3, !prof !0
;; 2:
;; br i1 %0, label %4, label %3, !prof !1
;; 3:
;; unreachable
;; 4:
;; ret void
;; }
;;!0 = !{!"branch_weights", i32 1, i32 2}
;;!1 = !{!"branch_weights", i32 1, i32 2, i32 3}
; RUN: llvm-dis %S/Inputs/branch-weight.bc -o - | FileCheck %s
; CHECK: !prof !0
; CHECK: !0 = !{!"branch_weights", i32 1, i32 2}
; CHECK-NOT: !prof !1
; CHECK-NOT: !1 = !{!"branch_weights", i32 1, i32 2, i32 3}