From e480bca2400d891bbde62e68d6a8f573848c22c6 Mon Sep 17 00:00:00 2001 From: Justin Squirek Date: Mon, 12 Oct 2020 12:06:08 -0400 Subject: [PATCH] [Ada] Crash on right shift operator for signed integers gcc/ada/ * doc/gnat_rm/intrinsic_subprograms.rst (Shifts and Rotates): Document behavior on negative numbers * gnat_rm.texi: Regenerate. * sem_eval.adb (Fold_Shift): Set modulus to be based on the RM size for non-modular integer types. --- gcc/ada/doc/gnat_rm/intrinsic_subprograms.rst | 4 +++- gcc/ada/gnat_rm.texi | 4 +++- gcc/ada/sem_eval.adb | 22 ++++++++++++++----- 3 files changed, 22 insertions(+), 8 deletions(-) diff --git a/gcc/ada/doc/gnat_rm/intrinsic_subprograms.rst b/gcc/ada/doc/gnat_rm/intrinsic_subprograms.rst index bf9f0b9e6d9..e448816572f 100644 --- a/gcc/ada/doc/gnat_rm/intrinsic_subprograms.rst +++ b/gcc/ada/doc/gnat_rm/intrinsic_subprograms.rst @@ -217,7 +217,9 @@ The formal parameter names can be anything. A more convenient way of providing these shift operators is to use the Provide_Shift_Operators pragma, which provides the function declarations -and corresponding pragma Import's for all five shift functions. +and corresponding pragma Import's for all five shift functions. Note that in +using these provided shift operations, shifts performed on negative numbers +will result in modification of the sign bit. .. _Source_Location: diff --git a/gcc/ada/gnat_rm.texi b/gcc/ada/gnat_rm.texi index 24afe79993d..decca9ef63f 100644 --- a/gcc/ada/gnat_rm.texi +++ b/gcc/ada/gnat_rm.texi @@ -17862,7 +17862,9 @@ The formal parameter names can be anything. A more convenient way of providing these shift operators is to use the Provide_Shift_Operators pragma, which provides the function declarations -and corresponding pragma Import's for all five shift functions. +and corresponding pragma Import's for all five shift functions. Note that in +using these provided shift operations, shifts performed on negative numbers +will result in modification of the sign bit. @node Source_Location,,Shifts and Rotates,Intrinsic Subprograms @anchor{gnat_rm/intrinsic_subprograms source-location}@anchor{271}@anchor{gnat_rm/intrinsic_subprograms id13}@anchor{272} diff --git a/gcc/ada/sem_eval.adb b/gcc/ada/sem_eval.adb index a04c5fa513c..52aa8c111da 100644 --- a/gcc/ada/sem_eval.adb +++ b/gcc/ada/sem_eval.adb @@ -4815,13 +4815,23 @@ package body Sem_Eval is if Op = N_Op_Shift_Left then Check_Elab_Call; - -- Fold Shift_Left (X, Y) by computing (X * 2**Y) rem modulus + declare + Modulus : Uint; + begin + if Is_Modular_Integer_Type (Typ) then + Modulus := Einfo.Modulus (Typ); + else + Modulus := Uint_2 ** RM_Size (Typ); + end if; - Fold_Uint - (N, - (Expr_Value (Left) * (Uint_2 ** Expr_Value (Right))) - rem Modulus (Typ), - Static => Static); + -- Fold Shift_Left (X, Y) by computing (X * 2**Y) rem modulus + + Fold_Uint + (N, + (Expr_Value (Left) * (Uint_2 ** Expr_Value (Right))) + rem Modulus, + Static => Static); + end; elsif Op = N_Op_Shift_Right then Check_Elab_Call; -- 2.30.2