102 lines
3.4 KiB
Diff
102 lines
3.4 KiB
Diff
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The cprop_hardreg pass is built around the assumption that accessing a
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register in a narrower mode is the same as accessing the lowpart of
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the register. This unfortunately is not true for vector registers on
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IBM Z. This caused a miscompile of LLVM with GCC 8.5. The problem
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could not be reproduced with upstream GCC unfortunately but we have to
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assume that it is latent there. The right fix would require
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substantial changes to the cprop pass and is certainly something we
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would want for our platform. But since this would not be acceptable
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for older GCCs I'll go with what Vladimir proposed in the RedHat BZ
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and introduce a hopefully temporary and undocumented target hook to
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disable that specific transformation in regcprop.c.
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--- a/gcc/config/s390/s390.c
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+++ b/gcc/config/s390/s390.c
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@@ -10488,6 +10488,18 @@ s390_hard_regno_mode_ok (unsigned int regno, machine_mode mode)
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return false;
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}
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+/* Implement TARGET_NARROW_MODE_REFERS_LOW_PART_P. */
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+
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+static bool
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+s390_narrow_mode_refers_low_part_p (unsigned int regno)
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+{
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+ if (reg_classes_intersect_p (VEC_REGS, REGNO_REG_CLASS (regno)))
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+ return false;
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+
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+ return true;
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+}
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+
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+
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/* Implement TARGET_MODES_TIEABLE_P. */
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static bool
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@@ -16956,6 +16968,9 @@ s390_case_values_threshold (void)
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#undef TARGET_CASE_VALUES_THRESHOLD
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#define TARGET_CASE_VALUES_THRESHOLD s390_case_values_threshold
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+#undef TARGET_NARROW_MODE_REFERS_LOW_PART_P
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+#define TARGET_NARROW_MODE_REFERS_LOW_PART_P s390_narrow_mode_refers_low_part_p
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+
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struct gcc_target targetm = TARGET_INITIALIZER;
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#include "gt-s390.h"
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--- a/gcc/regcprop.c
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+++ b/gcc/regcprop.c
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@@ -426,7 +426,8 @@ maybe_mode_change (machine_mode orig_mode, machine_mode copy_mode,
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if (orig_mode == new_mode)
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return gen_raw_REG (new_mode, regno);
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- else if (mode_change_ok (orig_mode, new_mode, regno))
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+ else if (mode_change_ok (orig_mode, new_mode, regno)
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+ && targetm.narrow_mode_refers_low_part_p (copy_regno))
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{
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int copy_nregs = hard_regno_nregs (copy_regno, copy_mode);
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int use_nregs = hard_regno_nregs (copy_regno, new_mode);
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--- a/gcc/target.def
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+++ b/gcc/target.def
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@@ -5446,6 +5446,16 @@ value that the middle-end intended.",
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bool, (machine_mode from, machine_mode to, reg_class_t rclass),
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hook_bool_mode_mode_reg_class_t_true)
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+/* This hook is used to work around a problem in regcprop. Hardcoded
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+assumptions currently prevent it from working correctly for targets
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+where the low part of a multi-word register doesn't align to accessing
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+the register with a narrower mode. */
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+DEFHOOK_UNDOC
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+(narrow_mode_refers_low_part_p,
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+"",
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+bool, (unsigned int regno),
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+hook_bool_uint_true)
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+
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/* Change pseudo allocno class calculated by IRA. */
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DEFHOOK
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(ira_change_pseudo_allocno_class,
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--- a/gcc/hooks.h
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+++ b/gcc/hooks.h
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@@ -86,6 +86,7 @@ extern void hook_void_tree (tree);
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extern void hook_void_tree_treeptr (tree, tree *);
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extern void hook_void_int_int (int, int);
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extern void hook_void_gcc_optionsp (struct gcc_options *);
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+extern bool hook_bool_uint_true (unsigned int);
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extern bool hook_bool_uint_uintp_false (unsigned int, unsigned int *);
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extern int hook_int_uint_mode_1 (unsigned int, machine_mode);
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--- a/gcc/hooks.c
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+++ b/gcc/hooks.c
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@@ -498,6 +498,14 @@ hook_void_gcc_optionsp (struct gcc_optio
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{
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}
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+/* Generic hook that takes an unsigned int and returns true. */
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+
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+bool
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+hook_bool_uint_true (unsigned int)
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+{
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+ return true;
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+}
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+
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/* Generic hook that takes an unsigned int, an unsigned int pointer and
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returns false. */
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