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Call reduce_vector_comparison_to_scalar_comparison earlier 

As noted in the PR, we can get an ICE after the introduction of code to reduce a vector comparison to a scalar.  The problem is we left the operand cache in an inconsistent state because we called the new function too late.   This is trivially fixed by making the transformation before we call update_stmt_if_modified.

The irony here is the whole point of calling reduce_vector_comparison_to_scalar_comparison when we did was to expose these kinds of secondary opportunities.  In this particular case we collapsed the test to a comparison of constants (thus no SSA operands).

Anyway, this fixes the problem in the obvious way.  This may all end up being moot if I can twiddle Richi's match.pd pattern to work.  It doesn't work as-written due to a couple issues that I haven't worked totally through yet.

Installed on the trunk after bootstrap & regression testing on x86 and verifying it addresses the aarch64 issue.

gcc/
	PR tree-optimization/102152
	* tree-ssa-dom.c (dom_opt_dom_walker::optimize_stmt): Reduce a vector
	comparison to a scalar comparison before calling
	update_stmt_if_modified.

gcc/testsuite/
	PR tree-optimization/102152
	* gcc.dg/pr102152.c: New test
This commit is contained in:
Jeff Law 2021-09-01 19:13:58 -04:00
parent a45786e9a3
commit 165446a1e8
2 changed files with 17 additions and 3 deletions
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14
gcc/testsuite/gcc.dg/pr102152.c Normal file
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@ -0,0 +1,14 @@
/* { dg-do compile } */
/* { dg-options "-O1 -ftree-loop-vectorize -fno-tree-fre" } */
/* { dg-additional-options "-march=armv8-a+sve" { target aarch64-*-* } } */
signed char i;
void
foo (void)
{
for (i = 0; i < 6; i += 5)
;
}

6
gcc/tree-ssa-dom.c
View File

@ -1990,14 +1990,14 @@ dom_opt_dom_walker::optimize_stmt (basic_block bb, gimple_stmt_iterator *si,
print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM);
}
update_stmt_if_modified (stmt);
opt_stats.num_stmts++;
/* STMT may be a comparison of uniform vectors that we can simplify
down to a comparison of scalars. Do that transformation first
so that all the scalar optimizations from here onward apply. */
reduce_vector_comparison_to_scalar_comparison (stmt);
update_stmt_if_modified (stmt);
opt_stats.num_stmts++;
/* Const/copy propagate into USES, VUSES and the RHS of VDEFs. */
cprop_into_stmt (stmt, m_evrp_range_analyzer);