[SanitizerCoverage] Replace the unconditional store with a load, then a conditional store.

Reviewers: vitalybuka, kcc

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D79392

Author: pratyai

llvm/lib/Transforms/Instrumentation/SanitizerCoverage.cpp

@@ -945,7 +945,12 @@ void ModuleSanitizerCoverage::InjectCoverageAtBlock(Function &F, BasicBlock &BB,
     auto FlagPtr = IRB.CreateGEP(
         FunctionBoolArray->getValueType(), FunctionBoolArray,
         {ConstantInt::get(IntptrTy, 0), ConstantInt::get(IntptrTy, Idx)});
-    auto Store = IRB.CreateStore(ConstantInt::getTrue(Int1Ty), FlagPtr);
+    auto Load = IRB.CreateLoad(Int1Ty, FlagPtr);
+    auto ThenTerm =
+        SplitBlockAndInsertIfThen(IRB.CreateIsNull(Load), &*IP, false);
+    IRBuilder<> ThenIRB(ThenTerm);
+    auto Store = ThenIRB.CreateStore(ConstantInt::getTrue(Int1Ty), FlagPtr);
+    SetNoSanitizeMetadata(Load);
     SetNoSanitizeMetadata(Store);
   }
   if (Options.StackDepth && IsEntryBB && !IsLeafFunc) {

llvm/test/Instrumentation/SanitizerCoverage/inline-bool-flag.ll

@@ -1,13 +1,23 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
 ; Test -sanitizer-coverage-inline-bool-flag=1
 ; RUN: opt < %s -sancov -sanitizer-coverage-level=1 -sanitizer-coverage-inline-bool-flag=1  -S | FileCheck %s
 ; RUN: opt < %s -passes='module(sancov-module)' -sanitizer-coverage-level=1 -sanitizer-coverage-inline-bool-flag=1  -S | FileCheck %s
 
 target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64"
 target triple = "x86_64-unknown-linux-gnu"
 define void @foo() {
+; CHECK-LABEL: @foo(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[TMP0:%.*]] = load i1, i1* getelementptr inbounds ([1 x i1], [1 x i1]* @__sancov_gen_, i64 0, i64 0), align 1, !nosanitize !1
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp eq i1 [[TMP0]], false
+; CHECK-NEXT:    br i1 [[TMP1]], label [[TMP2:%.*]], label [[TMP3:%.*]]
+; CHECK:       2:
+; CHECK-NEXT:    store i1 true, i1* getelementptr inbounds ([1 x i1], [1 x i1]* @__sancov_gen_, i64 0, i64 0), align 1, !nosanitize !1
+; CHECK-NEXT:    br label [[TMP3]]
+; CHECK:       3:
+; CHECK-NEXT:    ret void
+;
 entry:
-; CHECK: @__sancov_gen_ = private global [1 x i1] zeroinitializer, section "__sancov_bools", comdat($foo), align 1, !associated !0
-; CHECK: store i1 true, i1* getelementptr inbounds ([1 x i1], [1 x i1]* @__sancov_gen_, i64 0, i64 0), align 1, !nosanitize !1
   ret void
 }
 ; CHECK: call void @__sanitizer_cov_bool_flag_init(i1* bitcast (i1** @__start___sancov_bools to i1*), i1* bitcast (i1** @__stop___sancov_bools to i1*))