It is not trivial to decide when a write of a register pair terminates
or starts a new chain. For example, prior regrename we have
(insn 91 38 36 5 (set (reg:FPRX2 16 %f0 [orig:76 x ] [76])
(const_double:FPRX2 0.0 [0x0.0p+0]))
"float-cast-overflow-7-reduced.c":5:55 discrim 2 1507 {*movfprx2_64}
(expr_list:REG_EQUAL (const_double:FPRX2 0.0 [0x0.0p+0])
(nil)))
(insn 36 91 37 5 (set (subreg:DF (reg:FPRX2 16 %f0 [orig:76 x ] [76]) 0)
(mem/c:DF (plus:DI (reg/f:DI 15 %r15)
(const_int 160 [0xa0])) [7 %sfp+-32 S8 A64]))
"float-cast-overflow-7-reduced.c":5:55 discrim 2 1512 {*movdf_64dfp}
(nil))
(insn 37 36 43 5 (set (subreg:DF (reg:FPRX2 16 %f0 [orig:76 x ] [76]) 8)
(mem/c:DF (plus:DI (reg/f:DI 15 %r15)
(const_int 168 [0xa8])) [7 %sfp+-24 S8 A64]))
"float-cast-overflow-7-reduced.c":5:55 discrim 2 1512 {*movdf_64dfp}
(nil))
where insn 91 writes both registers of a register pair and it is clear
that an existing chain must be terminated and a new started. Insn 36
and 37 write only into one register of a corresponding register pair.
For each write on its own it is not obvious when to terminate an
existing chain and to start a new one. In other words, once insn 36
materializes and 37 didn't we are kind of in a limbo state. Tracking
this correctly is inherently hard and I'm not entirely sure whether
optimizations could even lead to more complicated cases where it is even
less clear when a chain terminates and a new has to be started.
Therefore, skip renaming of register pairs.
Bootstrapped and regtested on x86_64, aarch64, powerpc64le, and s390.
Ok for mainline?
This fixes on s390:
FAIL: g++.dg/cpp23/ext-floating14.C -std=gnu++23 execution test
FAIL: g++.dg/cpp23/ext-floating14.C -std=gnu++26 execution test
FAIL: c-c++-common/ubsan/float-cast-overflow-7.c -O2 execution test
FAIL: c-c++-common/ubsan/float-cast-overflow-7.c -O2 -flto
-fno-use-linker-plugin -flto-partition=none execution test
FAIL: c-c++-common/ubsan/float-cast-overflow-7.c -O2 -flto
-fuse-linker-plugin -fno-fat-lto-objects execution test
FAIL: gcc.dg/torture/fp-int-convert-float128-ieee-timode.c -O0 execution test
FAIL: gcc.dg/torture/fp-int-convert-float128-ieee-timode.c -O1 execution test
FAIL: gcc.dg/torture/fp-int-convert-float128-ieee-timode.c -O2 execution test
FAIL: gcc.dg/torture/fp-int-convert-float128-ieee-timode.c -O2 -flto
-fno-use-linker-plugin -flto-partition=none execution test
FAIL: gcc.dg/torture/fp-int-convert-float128-ieee-timode.c -O2 -flto
-fuse-linker-plugin -fno-fat-lto-objects execution test
FAIL: gcc.dg/torture/fp-int-convert-float128-ieee-timode.c -O3 -g execution
test
FAIL: gcc.dg/torture/fp-int-convert-float128-ieee-timode.c -Os execution test
FAIL: gcc.dg/torture/fp-int-convert-float64x-timode.c -O0 execution test
FAIL: gcc.dg/torture/fp-int-convert-float64x-timode.c -O1 execution test
FAIL: gcc.dg/torture/fp-int-convert-float64x-timode.c -O2 execution test
FAIL: gcc.dg/torture/fp-int-convert-float64x-timode.c -O2 -flto
-fno-use-linker-plugin -flto-partition=none execution test
FAIL: gcc.dg/torture/fp-int-convert-float64x-timode.c -O2 -flto
-fuse-linker-plugin -fno-fat-lto-objects execution test
FAIL: gcc.dg/torture/fp-int-convert-float64x-timode.c -O3 -g execution test
FAIL: gcc.dg/torture/fp-int-convert-float64x-timode.c -Os execution test
FAIL: gcc.dg/torture/fp-int-convert-timode.c -O0 execution test
FAIL: gcc.dg/torture/fp-int-convert-timode.c -O1 execution test
FAIL: gcc.dg/torture/fp-int-convert-timode.c -O2 execution test
FAIL: gcc.dg/torture/fp-int-convert-timode.c -O2 -flto -fno-use-linker-plugin
-flto-partition=none execution test
FAIL: gcc.dg/torture/fp-int-convert-timode.c -O2 -flto -fuse-linker-plugin
-fno-fat-lto-objects execution test
FAIL: gcc.dg/torture/fp-int-convert-timode.c -O3 -g execution test
FAIL: gcc.dg/torture/fp-int-convert-timode.c -Os execution test
FAIL: gfortran.dg/pr96711.f90 -O0 execution test
FAIL: TestSignalForwardingExternal
FAIL: go test misc/cgo/testcarchive
FAIL: libffi.closures/nested_struct5.c -W -Wall -Wno-psabi -O2 output pattern
test
FAIL: libphobos.phobos/std/algorithm/mutation.d execution test
FAIL: libphobos.phobos/std/conv.d execution test
FAIL: libphobos.phobos/std/internal/math/errorfunction.d execution test
FAIL: libphobos.phobos/std/variant.d execution test
FAIL: libphobos.phobos_shared/std/algorithm/mutation.d execution test
FAIL: libphobos.phobos_shared/std/conv.d execution test
FAIL: libphobos.phobos_shared/std/internal/math/errorfunction.d execution test
FAIL: libphobos.phobos_shared/std/variant.d execution test
gcc/ChangeLog:
PR rtl-optimiztion/115860
* regrename.cc (scan_rtx_reg): Do not try to rename register
pairs.
---
gcc/regrename.cc | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/gcc/regrename.cc b/gcc/regrename.cc
index 054e601740b..6ae5a2309d0 100644
--- a/gcc/regrename.cc
+++ b/gcc/regrename.cc
@@ -1113,6 +1113,10 @@ scan_rtx_reg (rtx_insn *insn, rtx *loc, enum reg_class
cl, enum scan_actions act
c = create_new_chain (this_regno, this_nregs, loc, insn, cl);
+ /* Give up early in case of register pairs. */
+ if (this_nregs != 1)
+ c->cannot_rename = 1;
+
/* We try to tie chains in a move instruction for
a single output. */
if (recog_data.n_operands == 2
--
2.45.2
