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amd64: add a spec rule for SHRL/SARL then CondS. gcc-8 has been seen to generate such things.

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This commit is contained in:
Julian Seward 2017-12-07 12:24:57 +01:00
parent 40f0364e1e
commit 8a2acb304d
1 changed files with 20 additions and 0 deletions
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20
VEX/priv/guest_amd64_helpers.c
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@ -1744,6 +1744,26 @@ IRExpr* guest_amd64_spechelper ( const HChar* function_name,
mkU32(0)));
}
if (isU64(cc_op, AMD64G_CC_OP_SHRL) && isU64(cond, AMD64CondS)) {
/* SHRL/SARL, then S --> (ULong)result[31] */
return binop(Iop_And64,
binop(Iop_Shr64, cc_dep1, mkU8(31)),
mkU64(1));
}
// The following looks correct to me, but never seems to happen because
// the front end converts jns to js by switching the fallthrough vs
// taken addresses. See jcc_01(). But then why do other conditions
// considered by this function show up in both variants (xx and Nxx) ?
//if (isU64(cc_op, AMD64G_CC_OP_SHRL) && isU64(cond, AMD64CondNS)) {
// /* SHRL/SARL, then NS --> (ULong) ~ result[31] */
// vassert(0);
// return binop(Iop_Xor64,
// binop(Iop_And64,
// binop(Iop_Shr64, cc_dep1, mkU8(31)),
// mkU64(1)),
// mkU64(1));
//}
/*---------------- COPY ----------------*/
/* This can happen, as a result of amd64 FP compares: "comisd ... ;
jbe" for example. */