[clang] [clang][Interp] Implement inc/dec for IntegralAP (PR #69597)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Timm Baeder (tbaederr)

<details>
<summary>Changes</summary>

The tests are commented out and I can't merge this yet, since it creates memory leaks when the interpretation is aborted midway through.

This problem also exists with floating-point values:

```c++
constexpr long double a() {
  long double A = __LDBL_MAX__;
  throw;
  return A;
}
```

We will allocate a `APFloat` into the stack frame and not call its destructor later.


---
Full diff: https://github.com/llvm/llvm-project/pull/69597.diff


2 Files Affected:

- (modified) clang/lib/AST/Interp/IntegralAP.h (+11-10) 
- (modified) clang/test/AST/Interp/intap.cpp (+55-7) 


``````````diff
diff --git a/clang/lib/AST/Interp/IntegralAP.h b/clang/lib/AST/Interp/IntegralAP.h
index 45e5b49546270aa..2e68c59ee80d436 100644
--- a/clang/lib/AST/Interp/IntegralAP.h
+++ b/clang/lib/AST/Interp/IntegralAP.h
@@ -116,7 +116,9 @@ template <bool Signed> class IntegralAP final {
 
   constexpr unsigned bitWidth() const { return V.getBitWidth(); }
 
-  APSInt toAPSInt(unsigned Bits = 0) const { return APSInt(V, Signed); }
+  APSInt toAPSInt(unsigned Bits = 0) const {
+    return APSInt(V, Signed).extend(Bits);
+  }
   APValue toAPValue() const { return APValue(APSInt(V, Signed)); }
 
   bool isZero() const { return V.isZero(); }
@@ -167,17 +169,13 @@ template <bool Signed> class IntegralAP final {
   }
 
   static bool increment(IntegralAP A, IntegralAP *R) {
-    // FIXME: Implement.
-    assert(false);
-    *R = IntegralAP(A.V - 1);
-    return false;
+    IntegralAP<Signed> One(1, A.bitWidth());
+    return add(A, One, A.bitWidth() + 1, R);
   }
 
   static bool decrement(IntegralAP A, IntegralAP *R) {
-    // FIXME: Implement.
-    assert(false);
-    *R = IntegralAP(A.V - 1);
-    return false;
+    IntegralAP<Signed> One(1, A.bitWidth());
+    return sub(A, One, A.bitWidth() + 1, R);
   }
 
   static bool add(IntegralAP A, IntegralAP B, unsigned OpBits, IntegralAP *R) {
@@ -246,7 +244,10 @@ template <bool Signed> class IntegralAP final {
 
   static void shiftRight(const IntegralAP A, const IntegralAP B,
                          unsigned OpBits, IntegralAP *R) {
-    *R = IntegralAP(A.V.ashr(B.V.getZExtValue()));
+    if constexpr (Signed)
+      *R = IntegralAP(A.V.ashr(B.V.getZExtValue()));
+    else
+      *R = IntegralAP(A.V.lshr(B.V.getZExtValue()));
   }
 
 private:
diff --git a/clang/test/AST/Interp/intap.cpp b/clang/test/AST/Interp/intap.cpp
index 27fae1b904351ce..9d947a092bb7440 100644
--- a/clang/test/AST/Interp/intap.cpp
+++ b/clang/test/AST/Interp/intap.cpp
@@ -29,9 +29,17 @@ static_assert(UBitIntZero1 == 0, "");
 
 
 #ifdef __SIZEOF_INT128__
+typedef __int128 int128_t;
+typedef unsigned __int128 uint128_t;
+static const __uint128_t UINT128_MAX =__uint128_t(__int128_t(-1L));
+static_assert(UINT128_MAX == -1, "");
+
+static const __int128_t INT128_MAX = UINT128_MAX >> (__int128_t)1;
+static_assert(INT128_MAX != 0, "");
+static const __int128_t INT128_MIN = -INT128_MAX - 1;
+
 namespace i128 {
-  typedef __int128 int128_t;
-  typedef unsigned __int128 uint128_t;
+
   constexpr int128_t I128_1 = 12;
   static_assert(I128_1 == 12, "");
   static_assert(I128_1 != 10, "");
@@ -40,12 +48,7 @@ namespace i128 {
                                    // expected-note{{evaluates to}} \
                                    // ref-note{{evaluates to}}
 
-  static const __uint128_t UINT128_MAX =__uint128_t(__int128_t(-1L));
-  static_assert(UINT128_MAX == -1, "");
 
-  static const __int128_t INT128_MAX = UINT128_MAX >> (__int128_t)1;
-  static_assert(INT128_MAX != 0, "");
-  static const __int128_t INT128_MIN = -INT128_MAX - 1;
   constexpr __int128 A = INT128_MAX + 1; // expected-error {{must be initialized by a constant expression}} \
                                          // expected-note {{outside the range}} \
                                          // ref-error {{must be initialized by a constant expression}} \
@@ -118,4 +121,49 @@ namespace AddSubOffset {
   static_assert(*P2 == 1,"");
 }
 
+namespace IncDec {
+#if 0
+  constexpr int128_t maxPlus1(bool Pre) {
+    int128_t a = INT128_MAX;
+
+    if (Pre)
+      ++a; // ref-note {{value 170141183460469231731687303715884105728 is outside the range}} \
+           // expected-note {{value 170141183460469231731687303715884105728 is outside the range}}
+    else
+      a++;
+    return a;
+  }
+  static_assert(maxPlus1(true) == 0, ""); // ref-error {{not an integral constant expression}} \
+                                          // ref-note in call to}} \
+                                          // expected-error {{not an integral constant expression}} \
+                                          // expected-note in call to}}
+  static_assert(maxPlus1(false) == 0, ""); // ref-error {{not an integral constant expression}} \
+                                           // ref-note in call to}} \
+                                           // expected-error {{not an integral constant expression}} \
+                                           // expected-note in call to}}
+
+  constexpr int128_t inc1(bool Pre) {
+    int128_t A = 0;
+    if (Pre)
+      ++A;
+    else
+      A++;
+    return A;
+  }
+  static_assert(inc1(true) == 1, "");
+  static_assert(inc1(false) == 1, "");
+
+  constexpr int128_t dec1(bool Pre) {
+    int128_t A = 2;
+    if (Pre)
+      --A;
+    else
+      A--;
+    return A;
+  }
+  static_assert(dec1(true) == 1, "");
+  static_assert(dec1(false) == 1, "");
+#endif
+}
+
 #endif

``````````

</details>


https://github.com/llvm/llvm-project/pull/69597