* [PATCH 2/2] adjust phi-sources when merging BBs
2020-11-11 23:52 [PATCH 0/2] adjust phi-sources when merging BBs Luc Van Oostenryck
2020-11-11 23:52 ` [PATCH 1/2] add testcase for phi-adjusting during BB merge Luc Van Oostenryck
@ 2020-11-11 23:52 ` Luc Van Oostenryck
1 sibling, 0 replies; 3+ messages in thread
From: Luc Van Oostenryck @ 2020-11-11 23:52 UTC (permalink / raw)
To: linux-sparse; +Cc: Luc Van Oostenryck
When merging two basic blocks, it may happen that both of theses
blocks contain a phi-source for the same phi-node. In this case,
only the phi-source from the bottom BB must be taken in account,
it kinda overwrites the value from the top BB and the phi-source
from the top BB must be ignored, in fact it must be removed.
However, it is not the case and this extra phi-source creates
different kind of problems. Among other things, it hinders
further simplifications. For example, the following code:
extern int array[2];
static inline int stupid_select(int idx)
{
if (idx)
idx = 0;
return array[idx];
}
int select(void)
{
int d = stupid_select(-1);
return d;
}
should boil down to a simple dereference of the array with
an index of zero, like:
select:
load.32 %r8 <- 0[array]
ret.32 %r8
but currently gives:
select:
phisrc.32 %phi3(idx) <- $0xffffffff
phisrc.32 %phi4(idx) <- $0
phi.32 %r12(idx) <- %phi3(idx), %phi4(idx)
sext.64 %r5 <- (32) %r12(idx)
mul.64 %r6 <- %r5, $4
add.64 %r7 <- %r6, array
load.32 %r8 <- 0[%r7]
ret.32 %r8
This patch takes care of the problem by:
* when merging 2 BBs, check when reaching a phi-source in the bottom BB
* if one is found, look after sibling phi-sources
* remove such sibling if belonging to the top BB.
With this change, the code above gives:
select:
phisrc.32 %phi4(idx) <- $0
phi.32 %r12(idx) <- %phi4(idx)
sext.64 %r5 <- (32) %r12(idx)
mul.64 %r6 <- %r5, $4
add.64 %r7 <- %r6, array
load.32 %r8 <- 0[%r7]
ret.32 %r8
which can the be simplified into the expected result.
Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
---
flow.c | 28 +++++++++++++++++++++++++
validation/optim/merge_bbe-adjust_phi.c | 1 -
2 files changed, 28 insertions(+), 1 deletion(-)
diff --git a/flow.c b/flow.c
index ef8d04e5827f..a74769c37659 100644
--- a/flow.c
+++ b/flow.c
@@ -723,6 +723,32 @@ void vrfy_flow(struct entrypoint *ep)
assert(!entry);
}
+static void adjust_phi(struct basic_block *top, struct instruction *insn)
+{
+ struct pseudo_user *pu;
+
+ FOR_EACH_PTR(insn->target->users, pu) {
+ struct instruction *user;
+ pseudo_t phi;
+
+ if (!pu)
+ continue;
+ user = pu->insn;
+ assert(user->opcode == OP_PHI);
+ FOR_EACH_PTR(user->phi_list, phi) {
+ struct instruction *phisrc;
+
+ if (phi == VOID)
+ continue;
+ phisrc = phi->def;
+ if (phisrc->bb != top)
+ continue;
+ REPLACE_CURRENT_PTR(phi, VOID);
+ kill_instruction(phisrc);
+ } END_FOR_EACH_PTR(phi);
+ } END_FOR_EACH_PTR(pu);
+}
+
void pack_basic_blocks(struct entrypoint *ep)
{
struct basic_block *bb;
@@ -804,6 +830,8 @@ out:
if (!insn->bb)
continue;
assert(insn->bb == bb);
+ if (insn->opcode == OP_PHISOURCE)
+ adjust_phi(parent, insn);
insn->bb = parent;
add_instruction(&parent->insns, insn);
} END_FOR_EACH_PTR(insn);
diff --git a/validation/optim/merge_bbe-adjust_phi.c b/validation/optim/merge_bbe-adjust_phi.c
index de4c54cc6d49..6a8ebb73a62d 100644
--- a/validation/optim/merge_bbe-adjust_phi.c
+++ b/validation/optim/merge_bbe-adjust_phi.c
@@ -16,7 +16,6 @@ int select(void)
/*
* check-name: merge_bbe-adjust_phi
* check-command: test-linearize -Wno-decl $file
- * check-known-to-fail
*
* check-output-ignore
* check-output-excludes: phisrc\\.
--
2.29.2
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