[gcc r13-229] [Ada] Reject numeric literals with too big exponents

[gcc r13-229] [Ada] Reject numeric literals with too big exponents

[Pierre-Marie de Rodat]

https://gcc.gnu.org/g:3ad8cac47099983e9b24103e8327bc2518044877

commit r13-229-g3ad8cac47099983e9b24103e8327bc2518044877
Author: Etienne Servais <servais@adacore.com>
Date:   Tue Jan 18 15:45:40 2022 +0100

    [Ada] Reject numeric literals with too big exponents
    
    While the compiler can compute numeric literal with arbitrary large
    exponents, this may take ages and is most likely a typo. Better emit an
    error when we certainly expect it to take long. The chosen threshold
    takes about 100s to compute.
    
    gcc/ada/
    
            * scng.adb (Nlit): Error on big UI_Scale.

Diff:
---
 gcc/ada/scng.adb | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/gcc/ada/scng.adb b/gcc/ada/scng.adb
index d0fb7f1c1f6..676a4f2898c 100644
--- a/gcc/ada/scng.adb
+++ b/gcc/ada/scng.adb
@@ -772,6 +772,15 @@ package body Scng is
             if UI_Scale = 0 then
                Int_Literal_Value := UI_Num_Value;
 
+            --  When the exponent is large, computing is expected to take a
+            --  rather unreasonable time. We generate an error so that it
+            --  does not appear that the compiler has gotten stuck. Such a
+            --  large exponent is most likely a typo anyway.
+
+            elsif UI_Scale >= 800_000 then
+               Error_Msg_SC ("exponent too large");
+               Int_Literal_Value := No_Uint;
+
             --  Avoid doing possibly expensive calculations in cases like
             --  parsing 163E800_000# when semantics will not be done anyway.
             --  This is especially useful when parsing garbled input.