[PATCH] middle-end/101530 - fix shufflevector lowering

Richard Biener rguenther@suse.de
Mon Jan 10 11:21:43 GMT 2022


On Wed, 5 Jan 2022, Jeff Law wrote:

> 
> 
> On 1/5/2022 7:17 AM, Richard Biener via Gcc-patches wrote:
> > This makes __builtin_shufflevector lowering force the result
> > of the BIT_FIELD_REF lowpart operation to a temporary as to
> > fulfil the IL verifier constraint that BIT_FIELD_REFs should
> > be always in outermost handled component position.  Trying to
> > enforce this during gimplification isn't as straight-forward
> > as here where we know we're dealing with an rvalue.
> >
> > Bootstrap & regtest running on x86_64-unknown-linux-gnu - OK for trunk?
> >
> > Thanks,
> > Richard.
> >
> > 2022-01-05  Richard Biener  <rguenther@suse.de>
> >
> > 	PR middle-end/101530
> > gcc/c-family/
> >  * c-common.c (c_build_shufflevector): Wrap the BIT_FIELD_REF
> >  in a TARGET_EXPR to force a temporary.
> >
> > gcc/testsuite/
> >  * c-c++-common/builtin-shufflevector-3.c: New testcase.
> Seems quite reasonable to me.

So I forgot to mark the TARGET_EXPR as having TREE_SIDE_EFFECTS
which makes the C++ FE side elide the initialization after
wrapping the TARGET_EXPR inside a COMPOUND_EXPR.  Fixed as follows,
re-bootstrapped and tested on x86_64-unknown-linux-gnu and pushed.

Richard.

>From be59671c5624fe8bf21ddb0192e97ebdfa4db381 Mon Sep 17 00:00:00 2001
From: Richard Biener <rguenther@suse.de>
Date: Wed, 5 Jan 2022 15:13:33 +0100
Subject: [PATCH] middle-end/101530 - fix shufflevector lowering
To: gcc-patches@gcc.gnu.org

This makes __builtin_shufflevector lowering force the result
of the BIT_FIELD_REF lowpart operation to a temporary as to
fulfil the IL verifier constraint that BIT_FIELD_REFs should
be always in outermost handled component position.  Trying to
enforce this during gimplification isn't as straight-forward
as here where we know we're dealing with an rvalue.

FAIL: c-c++-common/torture/builtin-shufflevector-1.c   -O0  execution test

2022-01-05  Richard Biener  <rguenther@suse.de>

	PR middle-end/101530
gcc/c-family/
	* c-common.c (c_build_shufflevector): Wrap the BIT_FIELD_REF
	in a TARGET_EXPR to force a temporary.

gcc/testsuite/
	* c-c++-common/builtin-shufflevector-3.c: New testcase.
---
 gcc/c-family/c-common.c                           |  7 +++++++
 .../c-c++-common/builtin-shufflevector-3.c        | 15 +++++++++++++++
 2 files changed, 22 insertions(+)
 create mode 100644 gcc/testsuite/c-c++-common/builtin-shufflevector-3.c

diff --git a/gcc/c-family/c-common.c b/gcc/c-family/c-common.c
index 13341fa315e..4a6a4edb763 100644
--- a/gcc/c-family/c-common.c
+++ b/gcc/c-family/c-common.c
@@ -1243,6 +1243,13 @@ c_build_shufflevector (location_t loc, tree v0, tree v1,
       tree lpartt = build_vector_type (TREE_TYPE (ret_type), mask.length ());
       ret = build3_loc (loc, BIT_FIELD_REF,
 			lpartt, ret, TYPE_SIZE (lpartt), bitsize_zero_node);
+      /* Wrap the lowpart operation in a TARGET_EXPR so it gets a separate
+	 temporary during gimplification.  See PR101530 for cases where
+	 we'd otherwise end up with non-toplevel BIT_FIELD_REFs.  */
+      tree tem = create_tmp_var_raw (lpartt);
+      DECL_CONTEXT (tem) = current_function_decl;
+      ret = build4 (TARGET_EXPR, lpartt, tem, ret, NULL_TREE, NULL_TREE);
+      TREE_SIDE_EFFECTS (ret) = 1;
     }
 
   if (!c_dialect_cxx () && !wrap)
diff --git a/gcc/testsuite/c-c++-common/builtin-shufflevector-3.c b/gcc/testsuite/c-c++-common/builtin-shufflevector-3.c
new file mode 100644
index 00000000000..0c9bda689ef
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/builtin-shufflevector-3.c
@@ -0,0 +1,15 @@
+/* { dg-do compile } */
+
+typedef int __attribute__((__vector_size__ (sizeof(int)*4))) V;
+
+int
+foo(V v, int i)
+{
+  return __builtin_shufflevector (v, v, 2, 3)[i];
+}
+
+int
+bar(V v, int i)
+{
+  return __builtin_shufflevector(v, v, 4)[0] & i;
+}
-- 
2.31.1



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