58 lines
2.4 KiB
Diff
58 lines
2.4 KiB
Diff
commit d6a810760ec61ddedf15445457edbbe288536a2f
|
|
Author: Julian Seward <jseward@acm.org>
|
|
Date: Tue Dec 12 22:31:54 2017 +0100
|
|
|
|
Fix false positive with s390x cgijnl instruction testing against sign bit.
|
|
|
|
https://bugs.kde.org/show_bug.cgi?id=387712
|
|
|
|
When the cgij "compare immediate and branch relative" instruction
|
|
compares 0 <=signed dep1, that means dep1 >=signed 0, so it is a test
|
|
against the most significant bit of dep1. So only that bit needs
|
|
to be defined.
|
|
|
|
diff --git a/VEX/priv/guest_s390_helpers.c b/VEX/priv/guest_s390_helpers.c
|
|
index 4cccdec..aacd833 100644
|
|
--- a/VEX/priv/guest_s390_helpers.c
|
|
+++ b/VEX/priv/guest_s390_helpers.c
|
|
@@ -1818,6 +1818,13 @@ isC64(const IRExpr *expr)
|
|
return expr->tag == Iex_Const && expr->Iex.Const.con->tag == Ico_U64;
|
|
}
|
|
|
|
+static inline Bool
|
|
+isC64_exactly(const IRExpr *expr, ULong n)
|
|
+{
|
|
+ return expr->tag == Iex_Const && expr->Iex.Const.con->tag == Ico_U64
|
|
+ && expr->Iex.Const.con->Ico.U64 == n;
|
|
+}
|
|
+
|
|
|
|
/* The returned expression is NULL if no specialization was found. In that
|
|
case the helper function will be called. Otherwise, the expression has
|
|
@@ -1895,9 +1902,25 @@ guest_s390x_spechelper(const HChar *function_name, IRExpr **args,
|
|
}
|
|
/* cc_dep1 > cc_dep2 ----> cc_dep2 < cc_dep1 */
|
|
if (cond == 2 || cond == 2 + 1) {
|
|
+ /* If we ever need the counterpart of the bug387712 fix just
|
|
+ below, then here is the place. We'll need to give an
|
|
+ alternative expression for the case "cc_dep2 <s 0". From a
|
|
+ bit of simple testing, I've yet to see any such cases,
|
|
+ however. */
|
|
return unop(Iop_1Uto32, binop(Iop_CmpLT64S, cc_dep2, cc_dep1));
|
|
}
|
|
if (cond == 8 + 2 || cond == 8 + 2 + 1) {
|
|
+ if (isC64_exactly(cc_dep2, 0)) {
|
|
+ /* 0 <=signed dep1
|
|
+ --> dep1 >=signed 0
|
|
+ --> m.s.bit of dep1 == 0 */
|
|
+ /* See bug 387712. This is an old trick from gcc to extract
|
|
+ the most significant bit of a word. */
|
|
+ return unop(Iop_64to32,
|
|
+ binop(Iop_Xor64,
|
|
+ binop(Iop_Shr64, cc_dep1, mkU8(63)),
|
|
+ mkU64(1)));
|
|
+ }
|
|
return unop(Iop_1Uto32, binop(Iop_CmpLE64S, cc_dep2, cc_dep1));
|
|
}
|
|
if (cond == 8 + 4 + 2 || cond == 8 + 4 + 2 + 1) {
|