[PATCH] D101391: [DSE] Eliminate zero memset after calloc

[Dávid Bolvanský via Phabricator via llvm-commits]

xbolva00 created this revision.
xbolva00 added a reviewer: fhahn.
Herald added a subscriber: hiraditya.
xbolva00 requested review of this revision.
Herald added a project: LLVM.
Herald added a subscriber: llvm-commits.

Solves PR11896

As noted, this can be improved futher (calloc -> malloc) in some cases. But for know, this is the first step.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D101391

Files:
  llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
  llvm/test/Transforms/DeadStoreElimination/noop-stores.ll


Index: llvm/test/Transforms/DeadStoreElimination/noop-stores.ll
===================================================================
--- llvm/test/Transforms/DeadStoreElimination/noop-stores.ll
+++ llvm/test/Transforms/DeadStoreElimination/noop-stores.ll
@@ -325,7 +325,6 @@
 ; CHECK-LABEL: @zero_memset_after_calloc(
 ; CHECK-NEXT:    [[CALL:%.*]] = tail call i8* @calloc(i64 10000, i64 4)
 ; CHECK-NEXT:    [[L0:%.*]] = bitcast i8* [[CALL]] to i32*
-; CHECK-NEXT:    call void @llvm.memset.p0i8.i64(i8* [[CALL]], i8 0, i64 40000, i1 false)
 ; CHECK-NEXT:    ret i8* [[CALL]]
 ;
   %call = tail call i8* @calloc(i64 10000, i64 4)
@@ -338,7 +337,6 @@
 ; CHECK-LABEL: @zero_memset_and_store_after_calloc(
 ; CHECK-NEXT:    [[CALL:%.*]] = tail call i8* @calloc(i64 10000, i64 4)
 ; CHECK-NEXT:    [[L0:%.*]] = bitcast i8* [[CALL]] to i32*
-; CHECK-NEXT:    call void @llvm.memset.p0i8.i64(i8* [[CALL]], i8 0, i64 40000, i1 false)
 ; CHECK-NEXT:    ret i8* [[CALL]]
 ;
   %call = tail call i8* @calloc(i64 10000, i64 4)
@@ -379,7 +377,6 @@
 ; CHECK-LABEL: @zero_memset_after_calloc_smaller_size(
 ; CHECK-NEXT:    [[CALL:%.*]] = tail call i8* @calloc(i64 10000, i64 4)
 ; CHECK-NEXT:    [[L0:%.*]] = bitcast i8* [[CALL]] to i32*
-; CHECK-NEXT:    call void @llvm.memset.p0i8.i64(i8* [[CALL]], i8 0, i64 20, i1 false)
 ; CHECK-NEXT:    ret i8* [[CALL]]
 ;
   %call = tail call i8* @calloc(i64 10000, i64 4)
@@ -395,7 +392,6 @@
 ; CHECK-LABEL: @memset_pattern16_after_calloc(
 ; CHECK-NEXT:    [[CALL:%.*]] = tail call i8* @calloc(i64 10000, i64 4)
 ; CHECK-NEXT:    [[L0:%.*]] = bitcast i8* [[CALL]] to i32*
-; CHECK-NEXT:    call void @llvm.memset.p0i8.i64(i8* align 4 [[CALL]], i8 0, i64 40000, i1 false)
 ; CHECK-NEXT:    call void @memset_pattern16(i8* [[CALL]], i8* [[PAT:%.*]], i64 40000)
 ; CHECK-NEXT:    ret i8* [[CALL]]
 ;
Index: llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
+++ llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
@@ -1770,6 +1770,26 @@
   bool storeIsNoop(MemoryDef *Def, const MemoryLocation &DefLoc,
                    const Value *DefUO) {
     StoreInst *Store = dyn_cast<StoreInst>(Def->getMemoryInst());
+    MemSetInst *MemSet = dyn_cast<MemSetInst>(Def->getMemoryInst());
+    Constant *StoredConstant = nullptr;
+    if (Store)
+      StoredConstant = dyn_cast<Constant>(Store->getOperand(0));
+    if (MemSet)
+      StoredConstant = dyn_cast<Constant>(MemSet->getValue());
+
+    if (StoredConstant && StoredConstant->isNullValue()) {
+      auto *DefUOInst = dyn_cast<Instruction>(DefUO);
+      if (DefUOInst && isCallocLikeFn(DefUOInst, &TLI)) {
+
+        auto *UnderlyingDef = cast<MemoryDef>(MSSA.getMemoryAccess(DefUOInst));
+        // If UnderlyingDef is the clobbering access of Def, no instructions
+        // between them can modify the memory location.
+        auto *ClobberDef =
+            MSSA.getSkipSelfWalker()->getClobberingMemoryAccess(Def);
+        return UnderlyingDef == ClobberDef;
+      }
+    }
+
     if (!Store)
       return false;
 
@@ -1817,18 +1837,6 @@
       }
     }
 
-    Constant *StoredConstant = dyn_cast<Constant>(Store->getOperand(0));
-    if (StoredConstant && StoredConstant->isNullValue()) {
-      auto *DefUOInst = dyn_cast<Instruction>(DefUO);
-      if (DefUOInst && isCallocLikeFn(DefUOInst, &TLI)) {
-        auto *UnderlyingDef = cast<MemoryDef>(MSSA.getMemoryAccess(DefUOInst));
-        // If UnderlyingDef is the clobbering access of Def, no instructions
-        // between them can modify the memory location.
-        auto *ClobberDef =
-            MSSA.getSkipSelfWalker()->getClobberingMemoryAccess(Def);
-        return UnderlyingDef == ClobberDef;
-      }
-    }
     return false;
   }
 };


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D101391.340942.patch
Type: text/x-patch
Size: 3828 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20210427/f2aef7c0/attachment.bin>