From 6d2eddf456f2d6494cac490c4aa3e7d089926098 Mon Sep 17 00:00:00 2001
From: Richard Biener <rguenther@suse.de>
Date: Wed, 28 Jun 2023 14:05:55 +0200
Subject: [PATCH] middle-end/110452 - bad code generation with AVX512 mask
 splat

The following adds an alternate way of expanding a uniform
mask vector constructor like

  _55 = _2 ? -1 : 0;
  vect_cst__56 = {_55, _55, _55, _55, _55, _55, _55, _55};

when the mask mode is a scalar int mode like for AVX512 or GCN.
Instead of piecewise building the result via shifts and ors
we can take advantage of uniformity and signedness of the
component and simply sign-extend to the result.

Instead of

        cmpl    $3, %edi
        sete    %cl
        movl    %ecx, %esi
        leal    (%rsi,%rsi), %eax
        leal    0(,%rsi,4), %r9d
        leal    0(,%rsi,8), %r8d
        orl     %esi, %eax
        orl     %r9d, %eax
        movl    %ecx, %r9d
        orl     %r8d, %eax
        movl    %ecx, %r8d
        sall    $4, %r9d
        sall    $5, %r8d
        sall    $6, %esi
        orl     %r9d, %eax
        orl     %r8d, %eax
        movl    %ecx, %r8d
        orl     %esi, %eax
        sall    $7, %r8d
        orl     %r8d, %eax
        kmovb   %eax, %k1

we then get

        cmpl    $3, %edi
        sete    %cl
	negl    %ecx
	kmovb   %ecx, %k1

Code generation for non-uniform masks remains bad, but at least
I see no easy way out for the most general case here.

	PR middle-end/110452
	* expr.cc (store_constructor): Handle uniform boolean
	vectors with integer mode specially.
---
 gcc/expr.cc                              | 13 +++++++++++++
 gcc/testsuite/gcc.target/i386/pr110452.c | 13 +++++++++++++
 2 files changed, 26 insertions(+)
 create mode 100644 gcc/testsuite/gcc.target/i386/pr110452.c

diff --git a/gcc/expr.cc b/gcc/expr.cc
index 62cd8facf756..b7f4e2fda9e6 100644
--- a/gcc/expr.cc
+++ b/gcc/expr.cc
@@ -7447,6 +7447,19 @@ store_constructor (tree exp, rtx target, int cleared, poly_int64 size,
 	      emit_move_insn (target, ops[0].value);
 	    break;
 	  }
+	/* Use sign-extension for uniform boolean vectors with
+	   integer modes.  */
+	if (!TREE_SIDE_EFFECTS (exp)
+	    && VECTOR_BOOLEAN_TYPE_P (type)
+	    && SCALAR_INT_MODE_P (mode)
+	    && (elt = uniform_vector_p (exp))
+	    && !VECTOR_TYPE_P (TREE_TYPE (elt)))
+	  {
+	    rtx op0 = force_reg (TYPE_MODE (TREE_TYPE (elt)),
+				 expand_normal (elt));
+	    convert_move (target, op0, 0);
+	    break;
+	  }
 
 	n_elts = TYPE_VECTOR_SUBPARTS (type);
 	if (REG_P (target)
diff --git a/gcc/testsuite/gcc.target/i386/pr110452.c b/gcc/testsuite/gcc.target/i386/pr110452.c
new file mode 100644
index 000000000000..8a3e2e560d2c
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr110452.c
@@ -0,0 +1,13 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -ftree-vectorize -fno-vect-cost-model -mavx512f -mprefer-vector-width=512" } */
+
+double a[1024], b[1024], c[1024];
+
+void foo (int flag, int n)
+{
+  _Bool x = flag == 3;
+  for (int i = 0; i < n; ++i)
+    a[i] = (x ? b[i] : c[i]) * 42.;
+}
+
+/* { dg-final { scan-assembler-not "\[^x\]orl" } } */
-- 
2.47.2