From 52441f18db7e051c16f2e6e12f415b93cb5450c4 Mon Sep 17 00:00:00 2001
From: Jakub Jelinek <jakub@redhat.com>
Date: Thu, 30 Dec 2021 14:35:06 +0100
Subject: [PATCH] emit-rtl: Fix a -fcompare-debug issue due to var-tracking
[PR103808]
We get a -fcompare-debug FAIL on the following testcase. The problem is
that during cprop we get when a TImode pseudo holding x is being
constructed:
(debug_insn 111 59 103 7 (var_location:TI D#2 (clobber (const_int 0 [0]))) -1
(nil))
(insn 103 111 110 7 (clobber (reg/v:TI 89 [ x ])) "pr103808.c":8:9 -1
(nil))
(debug_insn 110 103 104 7 (var_location:TI D#2 (subreg:TI (reg:DI 111 [ x ]) 0)) -1
(nil))
(insn 104 110 109 7 (set (subreg:DI (reg/v:TI 89 [ x ]) 0)
(reg:DI 111 [ x ])) "pr103808.c":8:9 80 {*movdi_internal}
(expr_list:REG_DEAD (reg:DI 111 [ x ])
(nil)))
Now, during RA that paradoxical subreg in a debug insn obviously can't
affect where pseudo 111 is allocated and RA puts it into the bp register,
so we have:
(debug_insn 110 111 109 4 (var_location:TI D#2 (reg:TI 6 bp [orig:111 x ] [111])) -1
(nil))
Now, during var-tracking when we for:
(debug_insn 25 23 26 3 (var_location:TI x (concatn/v:TI [
(reg:DI 6 bp [orig:111 x ] [111])
(subreg:DI (debug_expr:TI D#2) 8)
])) "pr103808.c":8:9 -1
(nil))
try to simplify the highpart subreg of bp, gen_rtx_REG_offset is called in:
if (HARD_REGISTER_NUM_P (final_regno))
{
rtx x = gen_rtx_REG_offset (op, outermode, final_regno,
subreg_memory_offset (outermode,
innermode, byte));
and that unfortunately sets REG_ATTRS on stack_pointer_rtx, because
gen_rtx_REG_offset uses gen_rtx_REG which for Pmode STACK_POINTER_REGNUM
returns stack_pointer_rtx rather than newly created register.
The clobbering of REG_ATTRS on the shared stack_pointer_rtx then shows up
in the dumps as (reg/f:DI 7 sp [ x+8 ]) instead of (reg/f:DI 7 sp)
that shows up without var-tracking.
Clobbering of REG_ATTRS on the shared *_pointer_rtx looks just wrong.
So, IMHO either simplify_gen_subreg -> gen_rtx_REG_offset should call
gen_raw_REG to make sure we get a new non-shared REG we can set REG_ATTRS
on, or we should make sure that we don't overwrite the REG_ATTRS on the
shared REGs (but then simplify_gen_subreg shouldn't try to overwrite
ORIGINAL_REGNO on those either).
For non-DEBUG_INSNs, I'd hope this never happens, the RA shouldn't allocate
multi-word regs overlapping with stack pointer, hard frame pointer etc.
2021-12-30 Jakub Jelinek <jakub@redhat.com>
PR debug/103808
* emit-rtl.c (gen_rtx_REG_offset): Use gen_raw_REG instead of
gen_rtx_REG.
* gcc.dg/pr103808.c: New test.
---
gcc/emit-rtl.c | 8 +++++++-
gcc/testsuite/gcc.dg/pr103808.c | 23 +++++++++++++++++++++++
2 files changed, 30 insertions(+), 1 deletion(-)
create mode 100644 gcc/testsuite/gcc.dg/pr103808.c
diff --git a/gcc/emit-rtl.c b/gcc/emit-rtl.c
index e6158f243c00..08c425007a1b 100644
--- a/gcc/emit-rtl.c
+++ b/gcc/emit-rtl.c
@@ -1261,7 +1261,13 @@ rtx
gen_rtx_REG_offset (rtx reg, machine_mode mode, unsigned int regno,
poly_int64 offset)
{
- rtx new_rtx = gen_rtx_REG (mode, regno);
+ /* Use gen_raw_REG rather than gen_rtx_REG, because otherwise we'd
+ overwrite REG_ATTRS (and in the callers often ORIGINAL_REGNO too)
+ of the shared REG rtxes like stack_pointer_rtx etc. This should
+ happen only for SUBREGs from DEBUG_INSNs, RA should ensure
+ multi-word registers don't overlap the special registers like
+ stack pointer. */
+ rtx new_rtx = gen_raw_REG (mode, regno);
update_reg_offset (new_rtx, reg, offset);
return new_rtx;
diff --git a/gcc/testsuite/gcc.dg/pr103808.c b/gcc/testsuite/gcc.dg/pr103808.c
new file mode 100644
index 000000000000..51fc460a9008
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr103808.c
@@ -0,0 +1,23 @@
+/* PR debug/103808 */
+/* { dg-do compile { target int128 } } */
+/* { dg-options "-fcompare-debug -O2 -ftrapv" } */
+
+void
+foo (__int128 x, int y)
+{
+ for (;;)
+ {
+ __int128 a, b;
+
+ x |= !!y;
+ a = x + 1;
+ b = y ? ++y : ++x;
+ y = a < b;
+ asm ("" : "+r" (y));
+ if (x >> 2)
+ y *= 2;
+
+ if (y == b)
+ __builtin_unreachable ();
+ }
+}
--
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