Re: [PATCH] tree-optimization/111807 - ICE in verify_sra_access_forest
> Am 13.12.2023 um 17:07 schrieb Martin Jambor : > > Hi, > > sorry for getting to this only so late, my email backlog from my medical > leave still isn't empty. > >> On Mon, Oct 16 2023, Richard Biener wrote: >> The following addresses build_reconstructed_reference failing to >> build references with a different offset than the models and thus >> the caller conditional being off. This manifests when attempting >> to build a ref with offset 160 from the model BIT_FIELD_REF >> onto the same base l_4827 but the models offset being 288. This >> cannot work for any kind of ref I can think of, not just with >> BIT_FIELD_REFs. >> >> Bootstrapped and tested on x86_64-unknown-linux-gnu, will push >> later. >> >> Martin - do you remember which case was supposed to be allowed >> with offset < model->offset? >> > > It happens quite often, even in our testsuite. In fact, the condition > is not even supposed to be necessary and is there just an early exit in > hopeless cases with malformed programs. > > The problem is that the function is used in two contexts and in one of > them we are not careful about ARRAY_REFs, as explained below in a commit > message of a patch I'd like to push. Needless to say, it has passed > bootstrap and testing on x86_64-linux, I'm running the same on > aarch64-linux. > > What do you think Thanks for the explanation. This wasn’t obvious. The patch is OK from my side. Thanks, Richard > Martin > > > > Subject: [PATCH] SRA: Relax requirements to use build_reconstructed_reference > (PR 111807) > > This patch half-reverts 3aaf704bca3e and replaces it with a fix with > relaxed requiremets for invoking build_reconstructed_reference in > build_ref_for_model. > > build_ref_for_model/build_ref_for_offset is used in two slightly > different contexts. The first is when we are looking at an assignment > like > > p->field_A.field_B = s.field_B; > > and we have a replacements for e.g. s.field_B.field_C.field_D and we > want to store them directly to p->field_A.field_B.field_C.field_D (as > opposed to going through s or using a MEM_REF based in > p->field_A.field_B). In this case, the offset of the > "model" (s.field_B.field_C.field_D) within this can be different than > offset within the LHS that we want to reach (field_C.field_D within > the "base" p->field_A.field_B). Patch 3aaf704bca3e has caused us to > unnecessarily create MEM_REFs for these situations. These uses of > build_ref_for_model work with the relaxed condition just fine. > > The second, problematic, context is when somewhere in the function we > have an assignment > > s.field_A = t.field_A.field_B; > > and we are creating an access structure to represent s.field_A.field_B > even if it is not actually accessed in the original input. This is > done after scanning the entire function body and we need to construct > a "universal" reference to s.field_A.field_B. In this case the "base" > is "s" and it has to be the DECL itself and not some reference for it > because for arbitrary references we need a GSI pointing to a statement > which we don't have, the reference is supposed to be universal. > > But then using build_ref_for_model and within it > build_reconstructed_reference misbehaves if the expression contains > any ARRAY_REFs. In the first case those are fine because as we > eventually reach the aggregate type that matches a real LHS or RHS, we > know we we can just bolt the rest of the references onto it and end up > with the correct overall reference. However when dealing with > > s.array[1].field_A = s.array[2].field_B; > > we cannot just bolt array[2] reference when we want array[1] but that > is exactly what happens when we use build_reconstructed_reference and > keep it walking all the way to s. > > I was considering making all users of the second kind use directly > build_ref_for_offset instead of build_ref_for_model but the latter > also handles COMPONENT_REFs to bit-fields which the former does not. > Therefore I have decided to use the NULL-ness of GSI as an indicator > how strict we need to be. I have changed the function comment to > reflect that. > > I have been able to observe disambiguation improvements with this patch > over current master, we do successfully manage a few more > aliasing_component_refs_p disambiguations when compiling cc1, going > from: > > Alias oracle query stats: >refs_may_alias_p: 94354287 disambiguations, 106279231 queries >ref_maybe_used_by_call_p: 1572511 disambiguations, 95618222 queries >call_may_clobber_ref_p: 649273 disambiguations, 659371 queries >stmt_kills_ref_p: 142342 kills, 8407309 queries >nonoverlapping_component_refs_p: 19 disambiguations, 10227 queries >nonoverlapping_refs_since_match_p: 15665 disambiguations, 52585 must > overlaps, 68893 queries >aliasing_component_refs_p: 67090 disambiguations, 3081766 queries >TBAA oracle: 22675296 disambiguations 61781978 queries > 14045969 are in
Re: [PATCH] tree-optimization/111807 - ICE in verify_sra_access_forest
Hi, sorry for getting to this only so late, my email backlog from my medical leave still isn't empty. On Mon, Oct 16 2023, Richard Biener wrote: > The following addresses build_reconstructed_reference failing to > build references with a different offset than the models and thus > the caller conditional being off. This manifests when attempting > to build a ref with offset 160 from the model BIT_FIELD_REF > onto the same base l_4827 but the models offset being 288. This > cannot work for any kind of ref I can think of, not just with > BIT_FIELD_REFs. > > Bootstrapped and tested on x86_64-unknown-linux-gnu, will push > later. > > Martin - do you remember which case was supposed to be allowed > with offset < model->offset? > It happens quite often, even in our testsuite. In fact, the condition is not even supposed to be necessary and is there just an early exit in hopeless cases with malformed programs. The problem is that the function is used in two contexts and in one of them we are not careful about ARRAY_REFs, as explained below in a commit message of a patch I'd like to push. Needless to say, it has passed bootstrap and testing on x86_64-linux, I'm running the same on aarch64-linux. What do you think? Martin Subject: [PATCH] SRA: Relax requirements to use build_reconstructed_reference (PR 111807) This patch half-reverts 3aaf704bca3e and replaces it with a fix with relaxed requiremets for invoking build_reconstructed_reference in build_ref_for_model. build_ref_for_model/build_ref_for_offset is used in two slightly different contexts. The first is when we are looking at an assignment like p->field_A.field_B = s.field_B; and we have a replacements for e.g. s.field_B.field_C.field_D and we want to store them directly to p->field_A.field_B.field_C.field_D (as opposed to going through s or using a MEM_REF based in p->field_A.field_B). In this case, the offset of the "model" (s.field_B.field_C.field_D) within this can be different than offset within the LHS that we want to reach (field_C.field_D within the "base" p->field_A.field_B). Patch 3aaf704bca3e has caused us to unnecessarily create MEM_REFs for these situations. These uses of build_ref_for_model work with the relaxed condition just fine. The second, problematic, context is when somewhere in the function we have an assignment s.field_A = t.field_A.field_B; and we are creating an access structure to represent s.field_A.field_B even if it is not actually accessed in the original input. This is done after scanning the entire function body and we need to construct a "universal" reference to s.field_A.field_B. In this case the "base" is "s" and it has to be the DECL itself and not some reference for it because for arbitrary references we need a GSI pointing to a statement which we don't have, the reference is supposed to be universal. But then using build_ref_for_model and within it build_reconstructed_reference misbehaves if the expression contains any ARRAY_REFs. In the first case those are fine because as we eventually reach the aggregate type that matches a real LHS or RHS, we know we we can just bolt the rest of the references onto it and end up with the correct overall reference. However when dealing with s.array[1].field_A = s.array[2].field_B; we cannot just bolt array[2] reference when we want array[1] but that is exactly what happens when we use build_reconstructed_reference and keep it walking all the way to s. I was considering making all users of the second kind use directly build_ref_for_offset instead of build_ref_for_model but the latter also handles COMPONENT_REFs to bit-fields which the former does not. Therefore I have decided to use the NULL-ness of GSI as an indicator how strict we need to be. I have changed the function comment to reflect that. I have been able to observe disambiguation improvements with this patch over current master, we do successfully manage a few more aliasing_component_refs_p disambiguations when compiling cc1, going from: Alias oracle query stats: refs_may_alias_p: 94354287 disambiguations, 106279231 queries ref_maybe_used_by_call_p: 1572511 disambiguations, 95618222 queries call_may_clobber_ref_p: 649273 disambiguations, 659371 queries stmt_kills_ref_p: 142342 kills, 8407309 queries nonoverlapping_component_refs_p: 19 disambiguations, 10227 queries nonoverlapping_refs_since_match_p: 15665 disambiguations, 52585 must overlaps, 68893 queries aliasing_component_refs_p: 67090 disambiguations, 3081766 queries TBAA oracle: 22675296 disambiguations 61781978 queries 14045969 are in alias set 0 10997085 queries asked about the same object 153 queries asked about the same alias set 0 access volatile 12485774 are dependent in the DAG 1577701 are aritificially in conflict with void * Modref stats: modref kill: 832 kills, 19399 queries
[PATCH] tree-optimization/111807 - ICE in verify_sra_access_forest
The following addresses build_reconstructed_reference failing to
build references with a different offset than the models and thus
the caller conditional being off. This manifests when attempting
to build a ref with offset 160 from the model BIT_FIELD_REF
onto the same base l_4827 but the models offset being 288. This
cannot work for any kind of ref I can think of, not just with
BIT_FIELD_REFs.
Bootstrapped and tested on x86_64-unknown-linux-gnu, will push
later.
Martin - do you remember which case was supposed to be allowed
with offset < model->offset?
Thanks,
Richard.
PR tree-optimization/111807
* tree-sra.cc (build_ref_for_model): Only call
build_reconstructed_reference when the offsets are the same.
* gcc.dg/torture/pr111807.c: New testcase.
---
gcc/testsuite/gcc.dg/torture/pr111807.c | 12
gcc/tree-sra.cc | 2 +-
2 files changed, 13 insertions(+), 1 deletion(-)
create mode 100644 gcc/testsuite/gcc.dg/torture/pr111807.c
diff --git a/gcc/testsuite/gcc.dg/torture/pr111807.c
b/gcc/testsuite/gcc.dg/torture/pr111807.c
new file mode 100644
index 000..09fbdcfb667
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr111807.c
@@ -0,0 +1,12 @@
+/* { dg-do compile } */
+
+static struct A {
+ int x : 4;
+} a;
+static int b;
+int main()
+{
+ struct A t[2];
+ t[0] = b ? t[1] : a;
+ return (b ? t[1].x : 0) && 1;
+}
diff --git a/gcc/tree-sra.cc b/gcc/tree-sra.cc
index 24d0c20da6a..f8dff8b27d7 100644
--- a/gcc/tree-sra.cc
+++ b/gcc/tree-sra.cc
@@ -1751,7 +1751,7 @@ build_ref_for_model (location_t loc, tree base,
HOST_WIDE_INT offset,
&& !TREE_THIS_VOLATILE (base)
&& (TYPE_ADDR_SPACE (TREE_TYPE (base))
== TYPE_ADDR_SPACE (TREE_TYPE (model->expr)))
- && offset <= model->offset
+ && offset == model->offset
/* build_reconstructed_reference can still fail if we have already
massaged BASE because of another type incompatibility. */
&& (res = build_reconstructed_reference (loc, base, model)))
--
2.35.3
