[gcc r10-9462] lra-constraints: Fix error-recovery for bad inline-asms [PR97971]

[Jakub Jelinek]

https://gcc.gnu.org/g:4dd7141653b57f638fc32291245d57d4dcfa3813

commit r10-9462-g4dd7141653b57f638fc32291245d57d4dcfa3813
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Wed Feb 3 09:07:36 2021 +0100

    lra-constraints: Fix error-recovery for bad inline-asms [PR97971]
    
    The following testcase has ice-on-invalid, it can't be reloaded, but we
    shouldn't ICE the compiler because the user typed non-sense.
    
    In current_insn_transform we have:
      if (process_alt_operands (reused_alternative_num))
        alt_p = true;
    
      if (check_only_p)
        return ! alt_p || best_losers != 0;
    
      /* If insn is commutative (it's safe to exchange a certain pair of
         operands) then we need to try each alternative twice, the second
         time matching those two operands as if we had exchanged them.  To
         do this, really exchange them in operands.
    
         If we have just tried the alternatives the second time, return
         operands to normal and drop through.  */
    
      if (reused_alternative_num < 0 && commutative >= 0)
        {
          curr_swapped = !curr_swapped;
          if (curr_swapped)
            {
              swap_operands (commutative);
              goto try_swapped;
            }
          else
            swap_operands (commutative);
        }
    
      if (! alt_p && ! sec_mem_p)
        {
          /* No alternative works with reloads??  */
          if (INSN_CODE (curr_insn) >= 0)
            fatal_insn ("unable to generate reloads for:", curr_insn);
          error_for_asm (curr_insn,
                         "inconsistent operand constraints in an %<asm%>");
          lra_asm_error_p = true;
    ...
    and so handle inline asms there differently (and delete/nullify them after
    this) - fatal_insn is only called for non-inline asm.
    But in process_alt_operands we do:
                    /* Both the earlyclobber operand and conflicting operand
                       cannot both be user defined hard registers.  */
                    if (HARD_REGISTER_P (operand_reg[i])
                        && REG_USERVAR_P (operand_reg[i])
                        && operand_reg[j] != NULL_RTX
                        && HARD_REGISTER_P (operand_reg[j])
                        && REG_USERVAR_P (operand_reg[j]))
                      fatal_insn ("unable to generate reloads for "
                                  "impossible constraints:", curr_insn);
    and thus ICE even for inline-asms.
    
    I think it is inappropriate to delete/nullify the insn in
    process_alt_operands, as it could be done e.g. in the check_only_p mode,
    so this patch just returns false in that case, which results in the
    caller have alt_p false, and as inline asm isn't simple move, sec_mem_p
    will be also false (and it isn't commutative either), so for check_only_p
    it will suggests to the callers it isn't ok and otherwise will emit
    error and delete/nullify the inline asm insn.
    
    2021-02-03  Jakub Jelinek  <jakub@redhat.com>
    
            PR middle-end/97971
            * lra-constraints.c (process_alt_operands): For inline asm, don't call
            fatal_insn, but instead return false.
    
            * gcc.target/i386/pr97971.c: New test.
    
    (cherry picked from commit eb69a49c4d3287e797e0d6279186221354905fe0)

Diff:
---
 gcc/lra-constraints.c                   |  9 +++++++--
 gcc/testsuite/gcc.target/i386/pr97971.c | 12 ++++++++++++
 2 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/gcc/lra-constraints.c b/gcc/lra-constraints.c
index bf04eb48ba6..7cc479b3042 100644
--- a/gcc/lra-constraints.c
+++ b/gcc/lra-constraints.c
@@ -3023,8 +3023,13 @@ process_alt_operands (int only_alternative)
 		    && operand_reg[j] != NULL_RTX
 		    && HARD_REGISTER_P (operand_reg[j])
 		    && REG_USERVAR_P (operand_reg[j]))
-		  fatal_insn ("unable to generate reloads for "
-			      "impossible constraints:", curr_insn);
+		  {
+		    /* For asm, let curr_insn_transform diagnose it.  */
+		    if (INSN_CODE (curr_insn) < 0)
+		      return false;
+		    fatal_insn ("unable to generate reloads for "
+				"impossible constraints:", curr_insn);
+		  }
 	      }
 	  if (last_conflict_j < 0)
 	    continue;
diff --git a/gcc/testsuite/gcc.target/i386/pr97971.c b/gcc/testsuite/gcc.target/i386/pr97971.c
new file mode 100644
index 00000000000..d07a31097c6
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr97971.c
@@ -0,0 +1,12 @@
+/* PR middle-end/97971 */
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+
+int
+foo (void)
+{
+  register _Complex long a asm ("rax");
+  register int b asm ("rdx");
+  asm ("# %0 %1" : "=&r" (a), "=r" (b));	/* { dg-error "inconsistent operand constraints in an 'asm'" } */
+  return a;
+}