From: Jakub Jelinek <jakub@redhat.com>
Date: Wed, 20 Mar 2024 09:55:07 +0000 (+0100)
Subject: bitint: Fix handling of conditional bitfield loads [PR114365]
X-Git-Tag: basepoints/gcc-15~569
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=456e10f28b36aa417e0db145556831c4f979fbd7;p=thirdparty%2Fgcc.git

bitint: Fix handling of conditional bitfield loads [PR114365]

For the m_var_msb (aka left shift) case of large/huge _BitInt bitfield loads
handle_load adds a PHI node, but I forgot to actually update the temporary
the code later on uses, so the PHI result was unused and the code
incorrectly used something that wasn't valid SSA form.
In particular, we emitted
  if (_29 != 2)
    goto <bb 4>; [80.00%]
  else
    goto <bb 5>; [20.00%]

  <bb 4> [local count: 1073741824]:
  _33 = VIEW_CONVERT_EXPR<unsigned long[3]>(s.D.2771)[_31];

  <bb 5> [local count: 1073741824]:
  # _34 = PHI <_33(4), 0(3)>
  _35 = _32 >> 31;
  _36 = _33 << 33;
  _37 = _36 | _35;
  _38 = _37 << _19;
where instead of _33 the _36 def stmt should be using _34.

Fixed thusly.

2024-03-20  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/114365
	* gimple-lower-bitint.cc (bitint_large_huge::handle_load): When adding
	a PHI node, set iv2 to its result afterwards.

	* gcc.dg/bitint-102.c: New test.
---

diff --git a/gcc/gimple-lower-bitint.cc b/gcc/gimple-lower-bitint.cc
index 40d814e5c38f..1ce13ca25799 100644
--- a/gcc/gimple-lower-bitint.cc
+++ b/gcc/gimple-lower-bitint.cc
@@ -2026,6 +2026,7 @@ bitint_large_huge::handle_load (gimple *stmt, tree idx)
 	      add_phi_arg (phi, build_zero_cst (m_limb_type),
 			   edge_false, UNKNOWN_LOCATION);
 	      m_gsi = gsi_after_labels (edge_true->dest);
+	      iv2 = iv3;
 	    }
 	}
       g = gimple_build_assign (make_ssa_name (m_limb_type), RSHIFT_EXPR,
diff --git a/gcc/testsuite/gcc.dg/bitint-102.c b/gcc/testsuite/gcc.dg/bitint-102.c
new file mode 100644
index 000000000000..9f9861ee2be5
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/bitint-102.c
@@ -0,0 +1,18 @@
+/* PR tree-optimization/114365 */
+/* { dg-do compile { target bitint } } */
+/* { dg-options "-std=c23 -O2" } */
+
+struct S {
+  int : 31;
+#if __BITINT_MAXWIDTH__ >= 129
+  _BitInt(129) b : 129;
+#else
+  _BitInt(63) b : 63;
+#endif
+} s;
+
+void
+foo (int a)
+{
+  s.b <<= a;
+}