Hi,
This patch adds a small improvement about sibling tail-calls. We producing
without that patch an useless load of address into register.
See for this the testcases sibcall-1.c, and sibcall-3.c. The testcase
sibcall-3.c is just an demonstration about other missed opportunities for
sibcall tail-calls and I added it to the testcases for completion. I test here
just 32-bit to make testcases simple. Nevertheless all those tests apply in
general to 64-bit, too.
This patch addresses partial the general issue shown in PR 60104. I will sent
with follow-up patches for it.
ChangeLog
2014-05-22 Kai Tietz <kti...@redhat.com>
PR target/60104
* config/i386/i386-protos.h (x86_sibcall_memory_p): New prototype.
* config/i386/i386.md (!SIBLING_CALL_P): Add alternative check
for x86_sibcall_memory_p.
* config/i386/i386.c (x86_sibcall_memory_p): New function.
(x86_sibcall_memory_p_1): New helper function.
(x86_output_mi_thunk): Allow memory if x86_sibcall_memory_p is true.
2014-05-22 Kai Tietz <kti...@redhat.com>
PR target/60104
* gcc.target/i386/sibcall-1.c: New test.
* gcc.target/i386/sibcall-2.c: New test.
* gcc.target/i386/sibcall-3.c: New test.
Regression-tested for x86_64-unknown-linux-gnu (multilib), x86_64-w64-mingw32,
and i686-pc-cygwin. Ok for apply?
Index: gcc/config/i386/i386-protos.h
===================================================================
--- gcc/config/i386/i386-protos.h (revision 210716)
+++ gcc/config/i386/i386-protos.h (working copy)
@@ -303,6 +303,7 @@ extern enum attr_cpu ix86_schedule;
#endif
extern const char * ix86_output_call_insn (rtx insn, rtx call_op);
+extern bool x86_sibcall_memory_p (rtx insn);
#ifdef RTX_CODE
/* Target data for multipass lookahead scheduling.
Index: gcc/config/i386/i386.c
===================================================================
--- gcc/config/i386/i386.c (revision 210716)
+++ gcc/config/i386/i386.c (working copy)
@@ -38752,6 +38752,69 @@ x86_can_output_mi_thunk (const_tree thunk ATTRIBUT
return true;
}
+/* Helper routine of x86_sibcall_memory_p.
+
+ RFLAGS is used to prevent to recurse on PLUS, and MULT expressions. */
+
+static bool
+x86_sibcall_memory_p_1 (rtx op, int rflags)
+{
+ switch (GET_CODE (op))
+ {
+ case SYMBOL_REF:
+ return true;
+ case MULT:
+ if (rflags & 2)
+ return false;
+
+ rflags |= 2; /* Mark to prevent recursion on MULT. */
+
+ if (x86_sibcall_memory_p_1 (XEXP (op, 0), rflags)
+ && x86_sibcall_memory_p_1 (XEXP (op, 1), rflags))
+ return true;
+ break;
+ case PLUS:
+ if (rflags & 1)
+ return false;
+
+ rflags |= 1; /* Makr to prevent recursion on PLUS. */
+
+ if (x86_sibcall_memory_p_1 (XEXP (op, 0), rflags)
+ && x86_sibcall_memory_p_1 (XEXP (op, 1), rflags))
+ return true;
+ break;
+ default:
+ if (REG_P (op))
+ {
+ op = GET_CODE (op) == SUBREG ? SUBREG_REG (op) : op;
+ return REGNO (op) == AX_REG;
+ }
+ else if (CONSTANT_P (op))
+ return true;
+ break;
+ }
+
+ return false;
+}
+
+/* Function returns TRUE if operand OP is an memory based on a
+ symbol-reference or based on accumulator-register.
+ Otherwise it returns FALSE. */
+
+bool
+x86_sibcall_memory_p (rtx op)
+{
+ if (!MEM_P (op))
+ return false;
+
+ op = XEXP (op, 0);
+
+ if (GET_CODE (op) == CONST)
+ op = XEXP (op, 0);
+
+ return x86_sibcall_memory_p_1 (op, 0);
+}
+
/* Output the assembler code for a thunk function. THUNK_DECL is the
declaration for the thunk function itself, FUNCTION is the decl for
the target function. DELTA is an immediate constant offset to be
@@ -38891,7 +38954,16 @@ x86_output_mi_thunk (FILE *file,
For our purposes here, we can get away with (ab)using a jump pattern,
because we're going to do no optimization. */
if (MEM_P (fnaddr))
- emit_jump_insn (gen_indirect_jump (fnaddr));
+ {
+ if (x86_sibcall_memory_p (fnaddr))
+ {
+ tmp = gen_rtx_CALL (VOIDmode, fnaddr, const0_rtx);
+ tmp = emit_call_insn (tmp);
+ SIBLING_CALL_P (tmp) = 1;
+ }
+ else
+ emit_jump_insn (gen_indirect_jump (fnaddr));
+ }
else
{
if (ix86_cmodel == CM_LARGE_PIC && SYMBOLIC_CONST (fnaddr))
Index: gcc/config/i386/i386.md
===================================================================
--- gcc/config/i386/i386.md (revision 210716)
+++ gcc/config/i386/i386.md (working copy)
@@ -11362,7 +11362,7 @@
(define_insn "*call"
[(call (mem:QI (match_operand:W 0 "call_insn_operand" "<c>zw"))
(match_operand 1))]
- "!SIBLING_CALL_P (insn)"
+ "!SIBLING_CALL_P (insn) || x86_sibcall_memory_p (operands[0])"
"* return ix86_output_call_insn (insn, operands[0]);"
[(set_attr "type" "call")])
@@ -11371,7 +11371,7 @@
[(call (mem:QI (match_operand:DI 0 "call_insn_operand" "rzw"))
(match_operand 1))
(unspec [(const_int 0)] UNSPEC_MS_TO_SYSV_CALL)])]
- "TARGET_64BIT && !SIBLING_CALL_P (insn)"
+ "TARGET_64BIT && (!SIBLING_CALL_P (insn) || x86_sibcall_memory_p
(operands[0]))"
"* return ix86_output_call_insn (insn, operands[0]);"
[(set_attr "type" "call")])
@@ -11401,7 +11401,7 @@
(set (reg:SI SP_REG)
(plus:SI (reg:SI SP_REG)
(match_operand:SI 2 "immediate_operand" "i")))]
- "!TARGET_64BIT && !SIBLING_CALL_P (insn)"
+ "!TARGET_64BIT && (!SIBLING_CALL_P (insn) || x86_sibcall_memory_p
(operands[0]))"
"* return ix86_output_call_insn (insn, operands[0]);"
[(set_attr "type" "call")])
@@ -11445,7 +11445,7 @@
[(set (match_operand 0)
(call (mem:QI (match_operand:W 1 "call_insn_operand" "<c>zw"))
(match_operand 2)))]
- "!SIBLING_CALL_P (insn)"
+ "!SIBLING_CALL_P (insn) || x86_sibcall_memory_p (operands[1])"
"* return ix86_output_call_insn (insn, operands[1]);"
[(set_attr "type" "callv")])
@@ -11463,7 +11463,7 @@
(call (mem:QI (match_operand:DI 1 "call_insn_operand" "rzw"))
(match_operand 2)))
(unspec [(const_int 0)] UNSPEC_MS_TO_SYSV_CALL)])]
- "TARGET_64BIT && !SIBLING_CALL_P (insn)"
+ "TARGET_64BIT && (!SIBLING_CALL_P (insn) || x86_sibcall_memory_p
(operands[1]))"
"* return ix86_output_call_insn (insn, operands[1]);"
[(set_attr "type" "callv")])
@@ -11488,7 +11488,7 @@
(set (reg:SI SP_REG)
(plus:SI (reg:SI SP_REG)
(match_operand:SI 3 "immediate_operand" "i")))]
- "!TARGET_64BIT && !SIBLING_CALL_P (insn)"
+ "!TARGET_64BIT && (!SIBLING_CALL_P (insn) || x86_sibcall_memory_p
(operands[1]))"
"* return ix86_output_call_insn (insn, operands[1]);"
[(set_attr "type" "callv")])
Index: gcc.target/i386/sibcall-1.c
===================================================================
--- gcc.target/i386/sibcall-1.c (revision 0)
+++ gcc.target/i386/sibcall-1.c (working copy)
@@ -0,0 +1,12 @@
+/* { dg-do compile } */
+/* { dg-require-effective-target ia32 } */
+/* { dg-options "-O2" } */
+
+extern int (*foo)(int);
+
+int boo (int a)
+{
+ return (*foo) (a);
+}
+
+/* { dg-final { scan-assembler-not "mov" } } */
Index: gcc.target/i386/sibcall-2.c
===================================================================
--- gcc.target/i386/sibcall-2.c (revision 0)
+++ gcc.target/i386/sibcall-2.c (working copy)
@@ -0,0 +1,16 @@
+/* { dg-do compile { xfail { *-*-* } } } */
+/* { dg-require-effective-target ia32 } */
+/* { dg-options "-O2" } */
+
+extern int doo1 (int);
+extern int doo2 (int);
+extern void bar (char *);
+
+int foo (int a)
+{
+ char s[256];
+ bar (s);
+ return (a < 0 ? doo1 : doo2) (a);
+}
+
+/* { dg-final { scan-assembler-not "call[ \t]*.%eax" } } */
Index: gcc.target/i386/sibcall-3.c
===================================================================
--- gcc.target/i386/sibcall-3.c (revision 0)
+++ gcc.target/i386/sibcall-3.c (working copy)
@@ -0,0 +1,16 @@
+/* { dg-do compile } */
+/* { dg-require-effective-target ia32 } */
+/* { dg-options "-O2" } */
+
+extern
+#ifdef _WIN32
+ __declspec (dllimport)
+#endif
+ void foo (int a);
+
+void bar (int a)
+{
+ return foo (a);
+}
+
+/* { dg-final { scan-assembler-not "jmp[ \t]*.%eax" } } */
