[PATCH] D128128: [GlobalOpt] Perform store->dominated load forwarding for stored once globals
Arthur Eubanks via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Sat Jun 18 16:17:12 PDT 2022
aeubanks created this revision.
aeubanks added a reviewer: nikic.
Herald added subscribers: ormris, hiraditya.
Herald added a project: All.
aeubanks requested review of this revision.
Herald added a project: LLVM.
Herald added a subscriber: llvm-commits.
Slight increase in lencod LTO compile time, otherwise neutral:
https://llvm-compile-time-tracker.com/compare.php?from=07b9937d0c5373a51fa24bf6b3efd8d7d74de050&to=079dbbfa97e4b281430c6cb0001fac742bfd05b0&stat=instructions
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D128128
Files:
llvm/lib/Transforms/IPO/GlobalOpt.cpp
llvm/test/Transforms/GlobalOpt/stored-once-forward-value.ll
Index: llvm/test/Transforms/GlobalOpt/stored-once-forward-value.ll
===================================================================
--- llvm/test/Transforms/GlobalOpt/stored-once-forward-value.ll
+++ llvm/test/Transforms/GlobalOpt/stored-once-forward-value.ll
@@ -10,10 +10,8 @@
define i1 @dom_const() {
; CHECK-LABEL: @dom_const(
-; CHECK-NEXT: store i1 true, ptr @g1, align 1
; CHECK-NEXT: call void @b()
-; CHECK-NEXT: [[R:%.*]] = load i1, ptr @g1, align 1
-; CHECK-NEXT: ret i1 [[R]]
+; CHECK-NEXT: ret i1 true
;
store i1 true, ptr @g1
call void @b()
@@ -23,10 +21,8 @@
define i32 @dom_arg(i32 %a) {
; CHECK-LABEL: @dom_arg(
-; CHECK-NEXT: store i32 [[A:%.*]], ptr @g2, align 4
; CHECK-NEXT: call void @b()
-; CHECK-NEXT: [[R:%.*]] = load i32, ptr @g2, align 4
-; CHECK-NEXT: ret i32 [[R]]
+; CHECK-NEXT: ret i32 [[A:%.*]]
;
store i32 %a, ptr @g2
call void @b()
Index: llvm/lib/Transforms/IPO/GlobalOpt.cpp
===================================================================
--- llvm/lib/Transforms/IPO/GlobalOpt.cpp
+++ llvm/lib/Transforms/IPO/GlobalOpt.cpp
@@ -1598,6 +1598,33 @@
if (optimizeOnceStoredGlobal(GV, StoredOnceValue, GS.Ordering, DL, GetTLI))
return true;
+ // If the store dominates any loads, those loads will always load the
+ // stored value (as opposed to the initializer), even in the presence of
+ // recursion. Restrict to the case where all loads/stores of the global are
+ // in the same function.
+ if (!GS.HasMultipleAccessingFunctions && GS.AccessingFunction) {
+ SmallVector<LoadInst *> Loads;
+ for (User *U : GV->users()) {
+ if (auto *LI = dyn_cast<LoadInst>(U))
+ Loads.push_back(LI);
+ }
+ // Only compute DT if we have any loads to examine.
+ bool MadeChange = false;
+ if (!Loads.empty()) {
+ auto &DT = LookupDomTree(*const_cast<Function *>(GS.AccessingFunction));
+ for (auto *LI : Loads) {
+ if (LI->getType() == StoredOnceValue->getType() &&
+ DT.dominates(GS.StoredOnceStore, LI)) {
+ LI->replaceAllUsesWith(StoredOnceValue);
+ LI->eraseFromParent();
+ MadeChange = true;
+ }
+ }
+ }
+ if (MadeChange)
+ return true;
+ }
+
// Otherwise, if the global was not a boolean, we can shrink it to be a
// boolean. Skip this optimization for AS that doesn't allow an initializer.
if (SOVConstant && GS.Ordering == AtomicOrdering::NotAtomic &&
-------------- next part --------------
A non-text attachment was scrubbed...
Name: D128128.438159.patch
Type: text/x-patch
Size: 2532 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20220618/a7905d9b/attachment-0001.bin>
More information about the llvm-commits
mailing list