[clang] 7787328 - [ubsan] Improve lowering of @llvm.allow.ubsan.check (#119013)

[via cfe-commits]

Author: Vitaly Buka
Date: 2024-12-07T16:12:58-08:00
New Revision: 7787328dd64c750c7acf30b86b31f0d7166c8f27

URL: https://github.com/llvm/llvm-project/commit/7787328dd64c750c7acf30b86b31f0d7166c8f27
DIFF: https://github.com/llvm/llvm-project/commit/7787328dd64c750c7acf30b86b31f0d7166c8f27.diff

LOG: [ubsan] Improve lowering of @llvm.allow.ubsan.check (#119013)

This fix the case, when single hot inlined callsite, prevent
checks for all other. This helps to reduce number of removed checks up
to 50% (deppedes on `cutoff-hot` value) .

`ScalarOptimizerLateEPCallback` was happening during
CGSCC walk, after each inlining, but this is effectively
after inlining.

Example, order in comments:

```
static void overflow() {
  // 1. Inline get/set if possible
  // 2. Simplify
  // 3. LowerAllowCheckPass
  set(get() + get());
}

void test() {
  // 4. Inline
  // 5. Nothing for LowerAllowCheckPass
  overflow();
}
```

With this patch it will look like:
```
static void overflow() {
  // 1. Inline get/set if possible
  // 2. Simplify
  set(get() + get());
}

void test() {
  // 3. Inline
  // 4. Simplify
  overflow();
}

// Later, after inliner CGSCC walk complete:
// 5. LowerAllowCheckPass for `overflow`
// 6. LowerAllowCheckPass for `test`
```

Added: 
    

Modified: 
    clang/lib/CodeGen/BackendUtil.cpp
    clang/test/CodeGen/allow-ubsan-check-inline.c

Removed: 
    


################################################################################
diff  --git a/clang/lib/CodeGen/BackendUtil.cpp b/clang/lib/CodeGen/BackendUtil.cpp
index fbb3fb6e5ea423..8cf44592a17475 100644
--- a/clang/lib/CodeGen/BackendUtil.cpp
+++ b/clang/lib/CodeGen/BackendUtil.cpp
@@ -789,13 +789,12 @@ static void addSanitizers(const Triple &TargetTriple,
   }
 
   if (LowerAllowCheckPass::IsRequested()) {
-    // We can optimize after inliner, and PGO profile matching. The hook below
-    // is called at the end `buildFunctionSimplificationPipeline`, which called
-    // from `buildInlinerPipeline`, which called after profile matching.
-    PB.registerScalarOptimizerLateEPCallback(
-        [](FunctionPassManager &FPM, OptimizationLevel Level) {
-          FPM.addPass(LowerAllowCheckPass());
-        });
+    // We want to call it after inline, which is about OptimizerEarlyEPCallback.
+    PB.registerOptimizerEarlyEPCallback([](ModulePassManager &MPM,
+                                           OptimizationLevel Level,
+                                           ThinOrFullLTOPhase Phase) {
+      MPM.addPass(createModuleToFunctionPassAdaptor(LowerAllowCheckPass()));
+    });
   }
 }
 

diff  --git a/clang/test/CodeGen/allow-ubsan-check-inline.c b/clang/test/CodeGen/allow-ubsan-check-inline.c
index cabe76d8034d77..1de24ab90dac0e 100644
--- a/clang/test/CodeGen/allow-ubsan-check-inline.c
+++ b/clang/test/CodeGen/allow-ubsan-check-inline.c
@@ -7,8 +7,8 @@ void set(int x);
 // We will only make decision in the `overflow` function.
 // NOINL-COUNT-1: remark: Allowed check:
 
-// FIXME: We will make decision on every inline.
-// INLINE-COUNT-1: remark: Allowed check:
+// We will make decision on every inline.
+// INLINE-COUNT-5: remark: Allowed check:
 
 static void overflow() {
   set(get() + get());