This patch implements despeculation on ARM. We only support it when
generating ARM or Thumb2 code (we need conditional execution); and we
only support it for sizes up to DImode. For unsupported cases we
fall back to the generic code generation sequence so that a suitable
failure warning is emitted.
* config/arm/arm.c (arm_inhibit_load_speculation): New function
(TARGET_INHIBIT_LOAD_SPECULATION): Redefine.
* config/arm/unspec.md (VUNSPEC_NOSPECULATE): New unspec_volatile code.
* config/arm/arm.md (cmp_ior): Make this pattern callable.
(nospeculate<QHSI:mode>, nospeculatedi): New patterns.
---
gcc/config/arm/arm.c | 108 ++++++++++++++++++++++++++++++++++++++++++++++
gcc/config/arm/arm.md | 40 ++++++++++++++++-
gcc/config/arm/unspecs.md | 1 +
3 files changed, 148 insertions(+), 1 deletion(-)
diff --git a/gcc/config/arm/arm.c b/gcc/config/arm/arm.c
index 7b3f4c1..393bfd6 100644
--- a/gcc/config/arm/arm.c
+++ b/gcc/config/arm/arm.c
@@ -308,6 +308,8 @@ static unsigned int arm_elf_section_type_flags (tree decl, const char *name,
int reloc);
static void arm_expand_divmod_libfunc (rtx, machine_mode, rtx, rtx, rtx *, rtx *);
static machine_mode arm_floatn_mode (int, bool);
+static rtx arm_inhibit_load_speculation (machine_mode, rtx, rtx, rtx, rtx,
+ rtx, rtx);
/* Table of machine attributes. */
static const struct attribute_spec arm_attribute_table[] =
@@ -766,6 +768,9 @@ static const struct attribute_spec arm_attribute_table[] =
#undef TARGET_CUSTOM_FUNCTION_DESCRIPTORS
#define TARGET_CUSTOM_FUNCTION_DESCRIPTORS 2
+#undef TARGET_INHIBIT_LOAD_SPECULATION
+#define TARGET_INHIBIT_LOAD_SPECULATION arm_inhibit_load_speculation
+
struct gcc_target targetm = TARGET_INITIALIZER;
/* Obstack for minipool constant handling. */
@@ -31112,4 +31117,107 @@ arm_coproc_ldc_stc_legitimate_address (rtx op)
}
return false;
}
+
+static rtx
+arm_inhibit_load_speculation (machine_mode mode, rtx result, rtx mem,
+ rtx lower_bound, rtx upper_bound,
+ rtx fail_result, rtx cmpptr)
+{
+ rtx cond, comparison;
+
+ /* We can't support this for Thumb1 as we have no suitable conditional
+ move operations. Nor do we support it for TImode. For both
+ these cases fall back to the generic code sequence which will emit
+ a suitable warning for us. */
+ if (mode == TImode || TARGET_THUMB1)
+ return default_inhibit_load_speculation (mode, result, mem, lower_bound,
+ upper_bound, fail_result, cmpptr);
+
+
+ rtx target = gen_reg_rtx (mode);
+ rtx tgt2 = result;
+
+ if (!register_operand (tgt2, mode))
+ tgt2 = gen_reg_rtx (mode);
+
+ if (!register_operand (cmpptr, ptr_mode))
+ cmpptr = force_reg (ptr_mode, cmpptr);
+
+ if (upper_bound == NULL)
+ {
+ if (!register_operand (lower_bound, ptr_mode))
+ lower_bound = force_reg (ptr_mode, lower_bound);
+
+ cond = arm_gen_compare_reg (LTU, cmpptr, lower_bound, NULL);
+ comparison = gen_rtx_LTU (VOIDmode, cond, const0_rtx);
+ }
+ else if (lower_bound == NULL)
+ {
+ if (!register_operand (upper_bound, ptr_mode))
+ upper_bound = force_reg (ptr_mode, upper_bound);
+
+ cond = arm_gen_compare_reg (GEU, cmpptr, upper_bound, NULL);
+ comparison = gen_rtx_GEU (VOIDmode, cond, const0_rtx);
+ }
+ else
+ {
+ /* We want to generate code for
+ result = (cmpptr < lower || cmpptr >= upper) ? 0 : *ptr;
+ Which can be recast to
+ result = (cmpptr < lower || upper <= cmpptr) ? 0 : *ptr;
+ which can be implemented as
+ cmp cmpptr, lower
+ cmpcs upper, cmpptr
+ bls 1f
+ ldr result, [ptr]
+ 1:
+ movls result, #0
+ with suitable IT instructions as needed for thumb2. Later
+ optimization passes may make the load conditional. */
+
+ if (!register_operand (lower_bound, ptr_mode))
+ lower_bound = force_reg (ptr_mode, lower_bound);
+
+ if (!register_operand (upper_bound, ptr_mode))
+ upper_bound = force_reg (ptr_mode, upper_bound);
+
+ rtx comparison1 = gen_rtx_LTU (SImode, cmpptr, lower_bound);
+ rtx comparison2 = gen_rtx_LEU (SImode, upper_bound, cmpptr);
+ cond = gen_rtx_REG (arm_select_dominance_cc_mode (comparison1,
+ comparison2,
+ DOM_CC_X_OR_Y),
+ CC_REGNUM);
+ emit_insn (gen_cmp_ior (cmpptr, lower_bound, upper_bound, cmpptr,
+ comparison1, comparison2, cond));
+ comparison = gen_rtx_NE (SImode, cond, const0_rtx);
+ }
+
+ rtx_code_label *label = gen_label_rtx ();
+ emit_jump_insn (gen_arm_cond_branch (label, comparison, cond));
+ emit_move_insn (target, mem);
+ emit_label (label);
+
+ insn_code icode;
+
+ switch (mode)
+ {
+ case QImode: icode = CODE_FOR_nospeculateqi; break;
+ case HImode: icode = CODE_FOR_nospeculatehi; break;
+ case SImode: icode = CODE_FOR_nospeculatesi; break;
+ case DImode: icode = CODE_FOR_nospeculatedi; break;
+ default:
+ gcc_unreachable ();
+ }
+
+ if (! insn_operand_matches (icode, 4, fail_result))
+ fail_result = force_reg (mode, fail_result);
+
+ emit_insn (GEN_FCN (icode) (tgt2, comparison, cond, target, fail_result));
+
+ if (tgt2 != result)
+ emit_move_insn (result, tgt2);
+
+ return result;
+}
+
#include "gt-arm.h"
diff --git a/gcc/config/arm/arm.md b/gcc/config/arm/arm.md
index f9365cd..7a6c134 100644
--- a/gcc/config/arm/arm.md
+++ b/gcc/config/arm/arm.md
@@ -9511,7 +9511,7 @@
(set_attr "type" "multiple")]
)
-(define_insn "*cmp_ior"
+(define_insn "cmp_ior"
[(set (match_operand 6 "dominant_cc_register" "")
(compare
(ior:SI
@@ -12054,6 +12054,44 @@
[(set_attr "length" "4")
(set_attr "type" "coproc")])
+(define_insn "nospeculate<QHSI:mode>"
+ [(set (match_operand:QHSI 0 "s_register_operand" "=l,l,r")
+ (unspec_volatile:QHSI
+ [(match_operator 1 "arm_comparison_operator"
+ [(match_operand 2 "cc_register" "") (const_int 0)])
+ (match_operand:QHSI 3 "s_register_operand" "0,0,0")
+ (match_operand:QHSI 4 "arm_not_operand" "I,K,r")]
+ VUNSPEC_NOSPECULATE))]
+ "TARGET_32BIT"
+ {
+ if (TARGET_THUMB)
+ return \"it\\t%d1\;mov%d1\\t%0, %4\;.inst 0xf3af8014\t%@ CSDB\";
+ return \"mov%d1\\t%0, %4\;.inst 0xe320f014\t%@ CSDB\";
+ }
+ [(set_attr "type" "mov_imm,mvn_imm,mov_reg")
+ (set_attr "conds" "use")
+ (set_attr "length" "8")]
+)
+
+(define_insn "nospeculatedi"
+ [(set (match_operand:DI 0 "s_register_operand" "=r")
+ (unspec_volatile:DI
+ [(match_operator 1 "arm_comparison_operator"
+ [(match_operand 2 "cc_register" "") (const_int 0)])
+ (match_operand:DI 3 "s_register_operand" "0")
+ (match_operand:DI 4 "arm_rhs_operand" "rI")]
+ VUNSPEC_NOSPECULATE))]
+ "TARGET_32BIT"
+ {
+ if (TARGET_THUMB)
+ return \"it\\t%d1\;mov%d1\\t%Q0, %Q4\;it\\t%d1\;mov%d1\\t%R0, %R4\;.inst 0xf3af8014\t%@ CSDB\";
+ return \"mov%d1\\t%Q0, %Q4\;mov%d1\\t%R0, %R4\;.inst 0xe320f014\t%@ CSDB\";
+ }
+ [(set_attr "type" "mov_reg")
+ (set_attr "conds" "use")
+ (set_attr "length" "12")]
+)
+
;; Vector bits common to IWMMXT and Neon
(include "vec-common.md")
;; Load the Intel Wireless Multimedia Extension patterns
diff --git a/gcc/config/arm/unspecs.md b/gcc/config/arm/unspecs.md
index 99cfa41..7f296ae 100644
--- a/gcc/config/arm/unspecs.md
+++ b/gcc/config/arm/unspecs.md
@@ -168,6 +168,7 @@
VUNSPEC_MCRR2 ; Represent the coprocessor mcrr2 instruction.
VUNSPEC_MRRC ; Represent the coprocessor mrrc instruction.
VUNSPEC_MRRC2 ; Represent the coprocessor mrrc2 instruction.
+ VUNSPEC_NOSPECULATE ; Represent a despeculation sequence.
])
;; Enumerators for NEON unspecs.
