combine: gen_lowpart_no_emit vs CLOBBER [PR120090]

The problem here is simplify-rtx.cc expects gen_lowpart_no_emit
to return NULL on failure but combine's hook was returning CLOBBER.
After r16-160-ge6f89d78c1a7528e93458278, gcc.target/i386/avx512bw-pr103750-2.c
started to fail at -m32 due to this as new simplify code would return
a RTL with a clobber in it rather than returning NULL.
To fix this gen_lowpart_no_emit should return NULL when there was an failure
instead of a clobber. This only changes the gen_lowpart_no_emit hook and not the
generic gen_lowpart hook as parts of combine just pass gen_lowpart result directly
without checking the return value.

Bootstrapped and tested on x86_64-linux-gnu.

	PR rtl-optimization/120090
gcc/ChangeLog:

	* combine.cc (gen_lowpart_for_combine_no_emit): New function.
	(RTL_HOOKS_GEN_LOWPART_NO_EMIT): Set to gen_lowpart_for_combine_no_emit.

Signed-off-by: Andrew Pinski <quic_apinski@quicinc.com>

diff --git a/gcc/combine.cc b/gcc/combine.cc
index 67cf0447607f6ed0cc4e0aa19525e9fc069bf1e2..4dbc1f6a4a4e0b8ef8a5d9403f4c2bdccdd42fee 100644 (file)
--- a/gcc/combine.cc
+++ b/gcc/combine.cc
@@ -458,6 +458,7 @@ static rtx simplify_shift_const (rtx, enum rtx_code, machine_mode, rtx,
                                 int);
 static int recog_for_combine (rtx *, rtx_insn *, rtx *, unsigned = 0, unsigned = 0);
 static rtx gen_lowpart_for_combine (machine_mode, rtx);
+static rtx gen_lowpart_for_combine_no_emit (machine_mode, rtx);
 static enum rtx_code simplify_compare_const (enum rtx_code, machine_mode,
                                             rtx *, rtx *);
 static enum rtx_code simplify_comparison (enum rtx_code, rtx *, rtx *);
@@ -491,7 +492,7 @@ static rtx gen_lowpart_or_truncate (machine_mode, rtx);
 
 /* Our implementation of gen_lowpart never emits a new pseudo.  */
 #undef RTL_HOOKS_GEN_LOWPART_NO_EMIT
-#define RTL_HOOKS_GEN_LOWPART_NO_EMIT      gen_lowpart_for_combine
+#define RTL_HOOKS_GEN_LOWPART_NO_EMIT      gen_lowpart_for_combine_no_emit
 
 #undef RTL_HOOKS_REG_NONZERO_REG_BITS
 #define RTL_HOOKS_REG_NONZERO_REG_BITS     reg_nonzero_bits_for_combine
@@ -11890,6 +11891,22 @@ gen_lowpart_for_combine (machine_mode omode, rtx x)
  fail:
   return gen_rtx_CLOBBER (omode, const0_rtx);
 }
+
+/* Like gen_lowpart_for_combine but returns NULL_RTX
+   for an error instead of CLOBBER.
+   Note no_emit is not called directly from combine but rather from
+   simplify_rtx and is expecting a NULL on failure rather than
+   a CLOBBER.  */
+
+static rtx
+gen_lowpart_for_combine_no_emit (machine_mode omode, rtx x)
+{
+  rtx tem = gen_lowpart_for_combine (omode, x);
+  if (!tem || GET_CODE (tem) == CLOBBER)
+    return NULL_RTX;
+  return tem;
+}
+
 \f
 /* Try to simplify a comparison between OP0 and a constant OP1,
    where CODE is the comparison code that will be tested, into a