[clang] [clang][Interp] Consider bit width in toAPSInt() (PR #71646)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Timm Baeder (tbaederr)

<details>
<summary>Changes</summary>

In `Interp.h`, when a add/sub/mul fails, we call this code and expect to get an `APSInt` back that can handle more than the current bitwidth of the type.

---
Full diff: https://github.com/llvm/llvm-project/pull/71646.diff


2 Files Affected:

- (modified) clang/lib/AST/Interp/IntegralAP.h (+9-1) 
- (modified) clang/test/AST/Interp/intap.cpp (+7-2) 


``````````diff
diff --git a/clang/lib/AST/Interp/IntegralAP.h b/clang/lib/AST/Interp/IntegralAP.h
index 6d301bad784af47..a24e283cb2e7cda 100644
--- a/clang/lib/AST/Interp/IntegralAP.h
+++ b/clang/lib/AST/Interp/IntegralAP.h
@@ -119,7 +119,15 @@ 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 {
+    if (Bits == 0)
+      Bits = bitWidth();
+
+    if constexpr (Signed)
+      return APSInt(V.sext(Bits), !Signed);
+    else
+      return APSInt(V.zext(Bits), !Signed);
+  }
   APValue toAPValue() const { return APValue(APSInt(V, Signed)); }
 
   bool isZero() const { return V.isZero(); }
diff --git a/clang/test/AST/Interp/intap.cpp b/clang/test/AST/Interp/intap.cpp
index 45961e6fc74b7a7..898d5795e1ffd5a 100644
--- a/clang/test/AST/Interp/intap.cpp
+++ b/clang/test/AST/Interp/intap.cpp
@@ -59,11 +59,16 @@ namespace i128 {
 
   static const __int128_t INT128_MAX = UINT128_MAX >> (__int128_t)1;
   static_assert(INT128_MAX != 0, "");
+  static_assert(INT128_MAX == 0, ""); // expected-error {{failed}} \
+                                      // expected-note {{evaluates to '170141183460469231731687303715884105727 == 0'}} \
+                                      // ref-error {{failed}} \
+                                      // ref-note {{evaluates to '170141183460469231731687303715884105727 == 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}} \
+                                         // expected-note {{value 170141183460469231731687303715884105728 is outside the range}} \
                                          // ref-error {{must be initialized by a constant expression}} \
-                                         // ref-note {{outside the range}}
+                                         // ref-note {{value 170141183460469231731687303715884105728 is outside the range}}
   constexpr int128_t Two = (int128_t)1 << 1ul;
   static_assert(Two == 2, "");
   static_assert(Two, "");

``````````

</details>


https://github.com/llvm/llvm-project/pull/71646