On Wed, May 21, 2025 at 11:48:34AM +0200, Uros Bizjak wrote:
> Please introduce "x86_64_neg_const_int_operand" predicate that will
> allow only const_int operands, and will reject negative endbr (and
> wide DImode) const_ints. You don't need a constraint if the predicate
> allows only const_ints (the const_int won't be reloaded).
>
> > + (const_int 0)))]
> > + "CONST_INT_P (operands[1])
> > + && ix86_match_ccmode (insn, CCGOCmode)
> > + && (<MODE>mode != DImode || !mode_signbit_p (SImode, operands[1]))
> > + && ((flag_cf_protection & CF_BRANCH) == 0
> > + || ((-INTVAL (operands[1]) & 0xffffffffUL)
> > + != (TARGET_64BIT ? 0xfa1e0ff3UL : 0xfb1e0ff3UL)))"
>
> New predicate will also avoid the above horrible insn condition.
So like this (if it passes bootstrap/regtest)?
Note, I'm using "n" rather than "<i>" constraints, because with "e" we could
get into trouble when the non-negated value would match endbr{64,32} - the
predicate only checks (I think that is desirable) that the negation isn't
endbr{64,32}.
2025-05-21 Jakub Jelinek <ja...@redhat.com>
PR target/120360
* config/i386/predicates.md (x86_64_neg_const_int_operand): New
predicate.
* config/i386/i386.md (*cmp<mode>_plus_1): New pattern.
* gcc.target/i386/pr120360.c: New test.
--- gcc/config/i386/predicates.md.jj 2025-05-20 08:14:05.053424802 +0200
+++ gcc/config/i386/predicates.md 2025-05-21 13:10:09.945333328 +0200
@@ -393,6 +393,23 @@ (define_predicate "x86_64_zext_immediate
return false;
})
+;; Return true if VALUE is a constant integer whose negation satisfies
+;; x86_64_immediate_operand.
+(define_predicate "x86_64_neg_const_int_operand"
+ (match_code "const_int")
+{
+ HOST_WIDE_INT val = -UINTVAL (op);
+ if (mode == DImode && trunc_int_for_mode (val, SImode) != val)
+ return false;
+ if (flag_cf_protection & CF_BRANCH)
+ {
+ unsigned HOST_WIDE_INT endbr = TARGET_64BIT ? 0xfa1e0ff3 : 0xfb1e0ff3;
+ if ((val & HOST_WIDE_INT_C (0xffffffff)) == endbr)
+ return false;
+ }
+ return true;
+})
+
;; Return true if VALUE is a constant integer whose low and high words satisfy
;; x86_64_immediate_operand.
(define_predicate "x86_64_hilo_int_operand"
--- gcc/config/i386/i386.md.jj 2025-05-20 08:14:05.036425035 +0200
+++ gcc/config/i386/i386.md 2025-05-21 13:04:12.441142398 +0200
@@ -1599,6 +1599,20 @@ (define_insn "*cmp<mode>_minus_1"
[(set_attr "type" "icmp")
(set_attr "mode" "<MODE>")])
+(define_insn "*cmp<mode>_plus_1"
+ [(set (reg FLAGS_REG)
+ (compare
+ (plus:SWI (match_operand:SWI 0 "nonimmediate_operand" "<r>m")
+ (match_operand:SWI 1 "x86_64_neg_const_int_operand" "n"))
+ (const_int 0)))]
+ "ix86_match_ccmode (insn, CCGOCmode)"
+{
+ operands[1] = gen_int_mode (-INTVAL (operands[1]), <MODE>mode);
+ return "cmp{<imodesuffix>}\t{%1, %0|%0, %1}";
+}
+ [(set_attr "type" "icmp")
+ (set_attr "mode" "<MODE>")])
+
(define_insn "*cmpqi_ext<mode>_1"
[(set (reg FLAGS_REG)
(compare
--- gcc/testsuite/gcc.target/i386/pr120360.c.jj 2025-05-20 20:40:32.194962716
+0200
+++ gcc/testsuite/gcc.target/i386/pr120360.c 2025-05-20 20:43:03.910930990
+0200
@@ -0,0 +1,36 @@
+/* PR target/120360 */
+/* { dg-do compile } */
+/* { dg-options "-O2 -fno-stack-protector -masm=att" } */
+/* { dg-additional-options "-fno-pic" { target { ! *-*-darwin* } } } */
+/* { dg-final { scan-assembler-times "\tjn*s\t" 3 } } */
+/* { dg-final { scan-assembler-times "\tcmp\[lq]\t%" 1 } } */
+/* { dg-final { scan-assembler-times "\tcmp\[lq]\t\\\$-1234," 1 } } */
+/* { dg-final { scan-assembler-times "\tcmp\[lq]\t\\\$2345," 1 } } */
+/* { dg-final { scan-assembler-not "\tadd\[lq]\t" { target { ! *-*-darwin* } }
} } */
+/* { dg-final { scan-assembler-not "\tsub\[lq]\t" { target { ! *-*-darwin* } }
} } */
+
+void qux (unsigned long);
+
+void
+foo (unsigned long x, unsigned long y)
+{
+ unsigned long z = x - y;
+ if ((long) z < 0)
+ qux (x);
+}
+
+void
+bar (unsigned long x)
+{
+ unsigned long z = x + 1234;
+ if ((long) z < 0)
+ qux (x);
+}
+
+void
+baz (unsigned long x)
+{
+ unsigned long z = x - 2345;
+ if ((long) z < 0)
+ qux (x);
+}
Jakub
