[PATCH] D116267: [DSE] Check for whole object overwrite even if dead store size not known
Nikita Popov via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Mon Jan 3 00:36:57 PST 2022
This revision was landed with ongoing or failed builds.
This revision was automatically updated to reflect the committed changes.
Closed by commit rG3478d64ee4bf: [DSE] Check for whole object overwrite even if dead store size not known (authored by nikic).
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D116267/new/
https://reviews.llvm.org/D116267
Files:
llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
llvm/test/Transforms/DeadStoreElimination/trivial-dse-calls.ll
Index: llvm/test/Transforms/DeadStoreElimination/trivial-dse-calls.ll
===================================================================
--- llvm/test/Transforms/DeadStoreElimination/trivial-dse-calls.ll
+++ llvm/test/Transforms/DeadStoreElimination/trivial-dse-calls.ll
@@ -252,14 +252,12 @@
ret void
}
-; TODO: We should be able to remove the call because while we don't know
-; the size of the write done by the call, we do know the following store
-; writes to the entire contents of the alloca.
+; We can remove the call because while we don't know the size of the write done
+; by the call, we do know the following store writes to the entire contents of
+; the alloca.
define i32 @test_dse_overwrite() {
; CHECK-LABEL: @test_dse_overwrite(
; CHECK-NEXT: [[A:%.*]] = alloca i32, align 4
-; CHECK-NEXT: [[BITCAST:%.*]] = bitcast i32* [[A]] to i8*
-; CHECK-NEXT: call void @f(i8* nocapture writeonly [[BITCAST]]) #[[ATTR1]]
; CHECK-NEXT: store i32 0, i32* [[A]], align 4
; CHECK-NEXT: [[V:%.*]] = load i32, i32* [[A]], align 4
; CHECK-NEXT: ret i32 [[V]]
Index: llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
+++ llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
@@ -835,6 +835,20 @@
if (!isGuaranteedLoopIndependent(DeadI, KillingI, DeadLoc))
return OW_Unknown;
+ const Value *DeadPtr = DeadLoc.Ptr->stripPointerCasts();
+ const Value *KillingPtr = KillingLoc.Ptr->stripPointerCasts();
+ const Value *DeadUndObj = getUnderlyingObject(DeadPtr);
+ const Value *KillingUndObj = getUnderlyingObject(KillingPtr);
+
+ // Check whether the killing store overwrites the whole object, in which
+ // case the size/offset of the dead store does not matter.
+ if (DeadUndObj == KillingUndObj && KillingLoc.Size.isPrecise()) {
+ uint64_t KillingUndObjSize = getPointerSize(KillingUndObj, DL, TLI, &F);
+ if (KillingUndObjSize != MemoryLocation::UnknownSize &&
+ KillingUndObjSize == KillingLoc.Size.getValue())
+ return OW_Complete;
+ }
+
// FIXME: Vet that this works for size upper-bounds. Seems unlikely that we'll
// get imprecise values here, though (except for unknown sizes).
if (!KillingLoc.Size.isPrecise() || !DeadLoc.Size.isPrecise()) {
@@ -875,14 +889,6 @@
return OW_Complete;
}
- // Check to see if the killing store is to the entire object (either a
- // global, an alloca, or a byval/inalloca argument). If so, then it clearly
- // overwrites any other store to the same object.
- const Value *DeadPtr = DeadLoc.Ptr->stripPointerCasts();
- const Value *KillingPtr = KillingLoc.Ptr->stripPointerCasts();
- const Value *DeadUndObj = getUnderlyingObject(DeadPtr);
- const Value *KillingUndObj = getUnderlyingObject(KillingPtr);
-
// If we can't resolve the same pointers to the same object, then we can't
// analyze them at all.
if (DeadUndObj != KillingUndObj) {
@@ -896,12 +902,6 @@
return OW_Unknown;
}
- // If the KillingI store is to a recognizable object, get its size.
- uint64_t KillingUndObjSize = getPointerSize(KillingUndObj, DL, TLI, &F);
- if (KillingUndObjSize != MemoryLocation::UnknownSize)
- if (KillingUndObjSize == KillingSize && KillingUndObjSize >= DeadSize)
- return OW_Complete;
-
// Okay, we have stores to two completely different pointers. Try to
// decompose the pointer into a "base + constant_offset" form. If the base
// pointers are equal, then we can reason about the two stores.
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