From aa454dda2eed4e71081bc57b1f32dfce2486b177 Mon Sep 17 00:00:00 2001
From: Balazs Benics <balazs.benics@sigmatechnology.se>
Date: Thu, 1 Jul 2021 10:54:22 +0200
Subject: [PATCH] [analyzer] LValueToRValueBitCasts should evaluate to an
 r-value

Previously `LValueToRValueBitCast`s were modeled in the same way how
a regular `BitCast` was. However, this should not produce an l-value.
Modeling bitcasts accurately is tricky, so it's probably better to
model this expression by binding a fresh conjured value.

The following code should not result in a diagnostic:
```lang=C++
  __attribute__((always_inline))
  static inline constexpr unsigned int_castf32_u32(float __A) {
    return __builtin_bit_cast(unsigned int, __A); // no-warning
  }
```

Previously, it reported
`Address of stack memory associated with local variable '__A' returned
to caller [core.StackAddressEscape]`.

Differential Revision: https://reviews.llvm.org/D105017

Reviewed by: NoQ, vsavchenko
---
 clang/lib/StaticAnalyzer/Core/ExprEngineC.cpp |  5 +++--
 clang/test/Analysis/builtin_bitcast.cpp       | 32 +++++++++++++++++++++++++++
 2 files changed, 35 insertions(+), 2 deletions(-)
 create mode 100644 clang/test/Analysis/builtin_bitcast.cpp

diff --git a/clang/lib/StaticAnalyzer/Core/ExprEngineC.cpp b/clang/lib/StaticAnalyzer/Core/ExprEngineC.cpp
index a1c8128..bf3f8df 100644
--- a/clang/lib/StaticAnalyzer/Core/ExprEngineC.cpp
+++ b/clang/lib/StaticAnalyzer/Core/ExprEngineC.cpp
@@ -304,7 +304,8 @@ void ExprEngine::VisitCast(const CastExpr *CastE, const Expr *Ex,
   ExplodedNodeSet dstPreStmt;
   getCheckerManager().runCheckersForPreStmt(dstPreStmt, Pred, CastE, *this);
 
-  if (CastE->getCastKind() == CK_LValueToRValue) {
+  if (CastE->getCastKind() == CK_LValueToRValue ||
+      CastE->getCastKind() == CK_LValueToRValueBitCast) {
     for (ExplodedNodeSet::iterator I = dstPreStmt.begin(), E = dstPreStmt.end();
          I!=E; ++I) {
       ExplodedNode *subExprNode = *I;
@@ -332,6 +333,7 @@ void ExprEngine::VisitCast(const CastExpr *CastE, const Expr *Ex,
 
     switch (CastE->getCastKind()) {
       case CK_LValueToRValue:
+      case CK_LValueToRValueBitCast:
         llvm_unreachable("LValueToRValue casts handled earlier.");
       case CK_ToVoid:
         continue;
@@ -380,7 +382,6 @@ void ExprEngine::VisitCast(const CastExpr *CastE, const Expr *Ex,
       case CK_Dependent:
       case CK_ArrayToPointerDecay:
       case CK_BitCast:
-      case CK_LValueToRValueBitCast:
       case CK_AddressSpaceConversion:
       case CK_BooleanToSignedIntegral:
       case CK_IntegralToPointer:
diff --git a/clang/test/Analysis/builtin_bitcast.cpp b/clang/test/Analysis/builtin_bitcast.cpp
new file mode 100644
index 0000000..396e7ca
--- /dev/null
+++ b/clang/test/Analysis/builtin_bitcast.cpp
@@ -0,0 +1,32 @@
+// RUN: %clang_analyze_cc1 -triple x86_64-unknown-unknown -verify %s \
+// RUN:   -analyzer-checker=core,debug.ExprInspection
+
+template <typename T> void clang_analyzer_dump(T);
+
+__attribute__((always_inline)) static inline constexpr unsigned int _castf32_u32(float __A) {
+  return __builtin_bit_cast(unsigned int, __A); // no-warning
+}
+
+void test(int i) {
+  _castf32_u32(42);
+
+  float f = 42;
+
+  // Loading from a floating point value results in unknown,
+  // which later materializes as a conjured value.
+  auto g = __builtin_bit_cast(unsigned int, f);
+  clang_analyzer_dump(g);
+  // expected-warning-re@-1 {{{{^conj_\$[0-9]+{unsigned int,}}}}
+
+  auto g2 = __builtin_bit_cast(unsigned int, 42.0f);
+  clang_analyzer_dump(g2);
+  // expected-warning-re@-1 {{{{^conj_\$[0-9]+{unsigned int,}}}}
+
+  auto g3 = __builtin_bit_cast(unsigned int, i);
+  clang_analyzer_dump(g3);
+  // expected-warning-re@-1 {{{{^reg_\$[0-9]+<int i>}}}}
+
+  auto g4 = __builtin_bit_cast(unsigned long, &i);
+  clang_analyzer_dump(g4);
+  // expected-warning@-1 {{&i [as 64 bit integer]}}
+}
-- 
2.7.4