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Fix a memcheck anomaly observed by Nick: lazy propagation of

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undefinedness was not being done properly for scalar shifts and that
could have led to undefined-value errors being falsely reported in the
obscure case where the shift amount was undefined but the end result
of the shift was unused.  This commit handles shifts more in
accordance with the maximally-lazy V-bit-testing scheme used by the
rest of memcheck.



git-svn-id: svn://svn.valgrind.org/valgrind/trunk@4887
This commit is contained in:
Julian Seward 2005-10-07 09:49:53 +00:00
parent 2349f41c86
commit d1c79a1830
1 changed files with 53 additions and 16 deletions
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69
memcheck/mc_translate.c
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@ -1095,7 +1095,53 @@ IRAtom* expensiveAddSub ( MCEnv* mce,
/*------------------------------------------------------------*/
/*--- Helpers for dealing with vector primops. ---*/
/*--- Scalar shifts. ---*/
/*------------------------------------------------------------*/
/* Produce an interpretation for (aa << bb) (or >>s, >>u). The basic
idea is to shift the definedness bits by the original shift amount.
This introduces 0s ("defined") in new positions for left shifts and
unsigned right shifts, and copies the top definedness bit for
signed right shifts. So, conveniently, applying the original shift
operator to the definedness bits for the left arg is exactly the
right thing to do:
(qaa << bb)
However if the shift amount is undefined then the whole result
is undefined. Hence need:
(qaa << bb) `UifU` PCast(qbb)
If the shift amount bb is a literal than qbb will say 'all defined'
and the UifU and PCast will get folded out by post-instrumentation
optimisation.
*/
static IRAtom* scalarShift ( MCEnv* mce,
IRType ty,
IROp original_op,
IRAtom* qaa, IRAtom* qbb,
IRAtom* aa, IRAtom* bb )
{
tl_assert(isShadowAtom(mce,qaa));
tl_assert(isShadowAtom(mce,qbb));
tl_assert(isOriginalAtom(mce,aa));
tl_assert(isOriginalAtom(mce,bb));
tl_assert(sameKindedAtoms(qaa,aa));
tl_assert(sameKindedAtoms(qbb,bb));
return
assignNew(
mce, ty,
mkUifU( mce, ty,
assignNew(mce, ty, binop(original_op, qaa, bb)),
mkPCastTo(mce, ty, qbb)
)
);
}
/*------------------------------------------------------------*/
/*--- Helpers for dealing with vector primops. ---*/
/*------------------------------------------------------------*/
/* Vector pessimisation -- pessimise within each lane individually. */
@ -1764,26 +1810,17 @@ IRAtom* expr2vbits_Binop ( MCEnv* mce,
case Iop_CmpEQ8: case Iop_CmpNE8:
return mkPCastTo(mce, Ity_I1, mkUifU8(mce, vatom1,vatom2));
case Iop_Shl64: case Iop_Shr64: case Iop_Sar64:
return scalarShift( mce, Ity_I64, op, vatom1,vatom2, atom1,atom2 );
case Iop_Shl32: case Iop_Shr32: case Iop_Sar32:
/* Complain if the shift amount is undefined. Then simply
shift the first arg's V bits by the real shift amount. */
complainIfUndefined(mce, atom2);
return assignNew(mce, Ity_I32, binop(op, vatom1, atom2));
return scalarShift( mce, Ity_I32, op, vatom1,vatom2, atom1,atom2 );
case Iop_Shl16: case Iop_Shr16: case Iop_Sar16:
/* Same scheme as with 32-bit shifts. */
complainIfUndefined(mce, atom2);
return assignNew(mce, Ity_I16, binop(op, vatom1, atom2));
return scalarShift( mce, Ity_I16, op, vatom1,vatom2, atom1,atom2 );
case Iop_Shl8: case Iop_Shr8:
/* Same scheme as with 32-bit shifts. */
complainIfUndefined(mce, atom2);
return assignNew(mce, Ity_I8, binop(op, vatom1, atom2));
case Iop_Shl64: case Iop_Shr64: case Iop_Sar64:
/* Same scheme as with 32-bit shifts. */
complainIfUndefined(mce, atom2);
return assignNew(mce, Ity_I64, binop(op, vatom1, atom2));
return scalarShift( mce, Ity_I8, op, vatom1,vatom2, atom1,atom2 );
case Iop_AndV128:
uifu = mkUifUV128; difd = mkDifDV128;