aarch64: Validate register operands early in ldp fusion pass [PR113062]

We were missing validation of the candidate register operands in the
ldp/stp pass.  I was relying on recog rejecting such cases when we
formed the final pair insn, but the testcase shows that with
-fharden-conditionals we attempt to combine two insns with asm_operands,
both containing mem rtxes.  This then trips the assert:

gcc_assert (change->new_uses.is_valid ());

in the stp case as we aren't expecting to have (distinct) uses of mem in
the candidate stores.

While doing this I noticed that it seems more natural to have the
initial definition of mem_size closer to its first use in track_access,
so I moved that down.

gcc/ChangeLog:

	PR target/113062
	* config/aarch64/aarch64-ldp-fusion.cc
	(ldp_bb_info::track_access): Punt on accesses with invalid
	register operands, move definition of mem_size closer to its
	first use.

gcc/testsuite/ChangeLog:

	PR target/113062
	* gcc.dg/pr113062.c: New test.

2 files changed, 18 insertions, 3 deletions

diff --git a/gcc/config/aarch64/aarch64-ldp-fusion.cc b/gcc/config/aarch64/aarch64-ldp-fusion.cc
index 327ba4e..0e2c299 100644
--- a/gcc/config/aarch64/aarch64-ldp-fusion.cc
+++ b/gcc/config/aarch64/aarch64-ldp-fusion.cc
@@ -458,11 +458,14 @@ ldp_bb_info::track_access (insn_info *insn, bool load_p, rtx mem)
   if (!ldp_operand_mode_ok_p (mem_mode))
     return;
 
-  // Note ldp_operand_mode_ok_p already rejected VL modes.
-  const HOST_WIDE_INT mem_size = GET_MODE_SIZE (mem_mode).to_constant ();
-
   rtx reg_op = XEXP (PATTERN (insn->rtl ()), !load_p);
 
+  // Ignore the access if the register operand isn't suitable for ldp/stp.
+  if (load_p
+      ? !aarch64_ldp_reg_operand (reg_op, mem_mode)
+      : !aarch64_stp_reg_operand (reg_op, mem_mode))
+    return;
+
   // We want to segregate FP/SIMD accesses from GPR accesses.
   //
   // Before RA, we use the modes, noting that stores of constant zero
@@ -474,6 +477,8 @@ ldp_bb_info::track_access (insn_info *insn, bool load_p, rtx mem)
     : (GET_MODE_CLASS (mem_mode) != MODE_INT
        && (load_p || !aarch64_const_zero_rtx_p (reg_op)));
 
+  // Note ldp_operand_mode_ok_p already rejected VL modes.
+  const HOST_WIDE_INT mem_size = GET_MODE_SIZE (mem_mode).to_constant ();
   const lfs_fields lfs = { load_p, fpsimd_op_p, mem_size };
 
   if (track_via_mem_expr (insn, mem, lfs))
diff --git a/gcc/testsuite/gcc.dg/pr113062.c b/gcc/testsuite/gcc.dg/pr113062.c
new file mode 100644
index 0000000..5667c17
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr113062.c
@@ -0,0 +1,10 @@
+/* { dg-do compile } */
+/* { dg-options "-Oz -fharden-conditional-branches" } */
+long double foo;
+double bar;
+void abort();
+void check() {
+  if (foo == bar)
+    abort();
+}
+