[PATCH] Fix ICE with x87 asm operands (PR inline-asm/68843)

[Bernd Edlinger]

Hi!

as described in the PR there are several non-intuitive rules that
one has to follow to avoid ICEs with x87 asm operands.

This patch adds an explicit rule, that avoids ICE in the first test case and
removes an unnecessary error message in the second test case.


Boot-strapped and regression-tested on x86_64-pc-linux-gnu.
OK for trunk?


Thanks
Bernd.
gcc:
2016-05-22  Bernd Edlinger  <bernd.edlin...@hotmail.de>

        PR inline-asm/68843
        * reg-stack.c (check_asm_stack_operands): Explicit input arguments
        must be grouped on top of stack.  Don't force early clobber
        on ordinary reg outputs.

testsuite:
2016-05-22  Bernd Edlinger  <bernd.edlin...@hotmail.de>

        PR inline-asm/68843
        * gcc.target/i386/pr68843-1.c: New test.
        * gcc.target/i386/pr68843-2.c: New test.

Index: gcc/reg-stack.c
===================================================================
--- gcc/reg-stack.c	(revision 231598)
+++ gcc/reg-stack.c	(working copy)
@@ -97,6 +97,9 @@
 	All implicitly popped input regs must be closer to the top of
 	the reg-stack than any input that is not implicitly popped.
 
+	All explicitly referenced input operands may not "skip" a reg.
+	Otherwise we can have holes in the stack.
+
    3. It is possible that if an input dies in an insn, reload might
       use the input reg for an output reload.  Consider this example:
 
@@ -461,6 +464,7 @@ check_asm_stack_operands (rtx_insn *insn)
 
   char reg_used_as_output[FIRST_PSEUDO_REGISTER];
   char implicitly_dies[FIRST_PSEUDO_REGISTER];
+  char explicitly_used[FIRST_PSEUDO_REGISTER];
 
   rtx *clobber_reg = 0;
   int n_inputs, n_outputs;
@@ -568,6 +572,7 @@ check_asm_stack_operands (rtx_insn *insn)
      popped.  */
 
   memset (implicitly_dies, 0, sizeof (implicitly_dies));
+  memset (explicitly_used, 0, sizeof (explicitly_used));
   for (i = n_outputs; i < n_outputs + n_inputs; i++)
     if (STACK_REG_P (recog_data.operand[i]))
       {
@@ -581,6 +586,8 @@ check_asm_stack_operands (rtx_insn *insn)
 
 	if (j < n_clobbers || op_alt[i].matches >= 0)
 	  implicitly_dies[REGNO (recog_data.operand[i])] = 1;
+	else if (reg_class_size[(int) op_alt[i].cl] == 1)
+	  explicitly_used[REGNO (recog_data.operand[i])] = 1;
       }
 
   /* Search for first non-popped reg.  */
@@ -600,6 +607,23 @@ check_asm_stack_operands (rtx_insn *insn)
       malformed_asm = 1;
     }
 
+  /* Search for first not-explicitly used reg.  */
+  for (i = FIRST_STACK_REG; i < LAST_STACK_REG + 1; i++)
+    if (! implicitly_dies[i] && ! explicitly_used[i])
+      break;
+
+  /* If there are any other explicitly used regs, that's an error.  */
+  for (; i < LAST_STACK_REG + 1; i++)
+    if (explicitly_used[i])
+      break;
+
+  if (i != LAST_STACK_REG + 1)
+    {
+      error_for_asm (insn,
+		     "explicitly used regs must be grouped at top of stack");
+      malformed_asm = 1;
+    }
+
   /* Enforce rule #3: If any input operand uses the "f" constraint, all
      output constraints must use the "&" earlyclobber.
 
@@ -607,7 +631,7 @@ check_asm_stack_operands (rtx_insn *insn)
      record any earlyclobber.  */
 
   for (i = n_outputs; i < n_outputs + n_inputs; i++)
-    if (op_alt[i].matches == -1)
+    if (op_alt[i].matches == -1 && STACK_REG_P (recog_data.operand[i]))
       {
 	int j;
 
Index: gcc/testsuite/gcc.target/i386/pr68843-1.c
===================================================================
--- gcc/testsuite/gcc.target/i386/pr68843-1.c	(revision 0)
+++ gcc/testsuite/gcc.target/i386/pr68843-1.c	(working copy)
@@ -0,0 +1,12 @@
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+
+double
+test ()
+{
+  double x = 1.0;
+  asm ("fld %1" /* { dg-error "explicitly used regs must be grouped at top of stack" } */
+       : "=&t" (x)
+       : "u" (x));
+  return x;
+}
Index: gcc/testsuite/gcc.target/i386/pr68843-2.c
===================================================================
--- gcc/testsuite/gcc.target/i386/pr68843-2.c	(revision 0)
+++ gcc/testsuite/gcc.target/i386/pr68843-2.c	(working copy)
@@ -0,0 +1,24 @@
+/* { dg-do run } */
+/* { dg-options "-O2" } */
+
+int
+test (double y)
+{
+  int a, b;
+  asm ("fistpl (%1)\n\t"
+       "movl (%1), %0"
+       : "=r" (a)
+       : "r" (&b), "t" (y)
+       : "st", "memory");
+  return a;
+}
+
+int 
+main ()
+{
+  int t;
+  for (t = -10; t < 10; t++)
+    if (test ((double)t) != t)
+      __builtin_abort ();  
+  return 0;
+}