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tree-optimization/115149 - VOP live and missing PHIs

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The following fixes a bug in vop-live get_live_in which was using
NULL to indicate the first processed edge but at the same time
using it for the case the live-in virtual operand cannot be computed.
The following fixes this, avoiding sinking a load to a place where
we'd have to insert virtual PHIs to make the virtual operand SSA
web OK.

	PR tree-optimization/115149
	* tree-ssa-live.cc (virtual_operand_live::get_live_in):
	Explicitly track the first processed edge.

	* gcc.dg/pr115149.c: New testcase.

(cherry picked from commit ec9b8bafe20755d13ab9a1b834b5da79ae972c0e)
This commit is contained in:
Richard Biener 2024-05-21 09:48:04 +02:00
parent 2a1fdd5fd0
commit 90a447677a
2 changed files with 22 additions and 2 deletions
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16
gcc/testsuite/gcc.dg/pr115149.c Normal file
View file

@ -0,0 +1,16 @@
/* { dg-do compile } */
/* { dg-options "-O3 -fno-inline -fno-tree-vrp -fno-ipa-sra -fno-tree-dce -fno-tree-ch" } */
int a, c, e, f, g, h[1], i;
static int j(int b) { return 0; }
static void k(int d) {}
int main()
{
if (h[0])
while (1) {
k(f && j(i && (h[g] = e)));
while (a)
c ^= 1;
}
return 0;
}

8
gcc/tree-ssa-live.cc
View file

@ -1684,14 +1684,18 @@ virtual_operand_live::get_live_in (basic_block bb)
edge_iterator ei;
edge e;
tree livein = NULL_TREE;
bool first = true;
FOR_EACH_EDGE (e, ei, bb->preds)
if (e->flags & EDGE_DFS_BACK)
/* We can ignore backedges since if there's a def there it would
have forced a PHI in the source because it also acts as use
downstream. */
continue;
else if (!livein)
livein = get_live_out (e->src);
else if (first)
{
livein = get_live_out (e->src);
first = false;
}
else if (get_live_out (e->src) != livein)
/* When there's no virtual use downstream this indicates a point
where we'd insert a PHI merging the different live virtual