[Valgrind-developers] [valgrind] s390x: Fix negative signed immediate operands in code gen

[Andreas A. <ar...@so...>]

https://sourceware.org/cgit/valgrind/commit/?id=dcf06a3908e20cab2691aa363689ed6effcc2f6a

commit dcf06a3908e20cab2691aa363689ed6effcc2f6a
Author: Andreas Arnez <ar...@li...>
Date:   Wed Mar 18 18:27:44 2026 +0100

    s390x: Fix negative signed immediate operands in code gen
    
    The helper functions that check whether an integer constant fits into a
    16-bit or 32-bit signed immediate operand always return false for negative
    values.  This prevents the use of negative immediate operands altogether
    and may lead to unnecessarily clumsy code being emitted, such as
    
      v-add    %r8,-160               8 bytes
      iihf      %r0,4294967295
      iilf      %r0,4294967136
      agr       %r8,%r0
    
    instead of
    
      v-add    %r8,-160               8 bytes
      aghi      %r8,-160
    
    This behavior is a regression; it was introduced by
    
      commit #0282c1cfc9015b69d09 -- s390: Tweak a few helper functions.
    
    However, the previous code was perhaps a bit obscure.  So instead of
    reverting to that, use simple checks like "val + 0x8000 <= 0xFFFF",
    exploiting standard C integer semantics.

Diff:
---
 VEX/priv/host_s390_defs.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/VEX/priv/host_s390_defs.c b/VEX/priv/host_s390_defs.c
index 28b66ef5c7..8ff386cc4a 100644
--- a/VEX/priv/host_s390_defs.c
+++ b/VEX/priv/host_s390_defs.c
@@ -4176,21 +4176,21 @@ s390_emit_RISBG(UChar *p, UChar r1, UChar r2, UChar i3, Char i4, UChar i5)
 static __inline__ Bool
 uint_fits_signed_16bit(UInt val)
 {
-   return val <= 0x7FFFu;
+   return val + 0x8000 <= 0xFFFF;
 }
 
 
 static __inline__ Bool
 ulong_fits_signed_16bit(ULong val)
 {
-   return val <= 0x7FFFu;
+   return val + 0x8000 <= 0xFFFF;
 }
 
 
 static __inline__ Bool
 ulong_fits_signed_32bit(ULong val)
 {
-   return val <= 0x7FFFFFFFu;
+   return val + 0x80000000 <= 0xFFFFFFFF;
 }