[PATCH] D136822: [InstCombine] Allow memcpys from constant memory to readonly noalias parameters to be elided.

[Patrick Walton via Phabricator via llvm-commits]

pcwalton updated this revision to Diff 471270.
pcwalton added a comment.

Addressed review comments.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D136822/new/

https://reviews.llvm.org/D136822

Files:
  llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
  llvm/test/Transforms/InstCombine/forward-memcpy-to-readonly.ll


Index: llvm/test/Transforms/InstCombine/forward-memcpy-to-readonly.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/InstCombine/forward-memcpy-to-readonly.ll
@@ -0,0 +1,23 @@
+; Tests that a local alloca that is the target of a memcpy from a constant that is
+; only passed as a readonly nocapture parameter can be eliminated.
+;
+; RUN: opt -S -passes=instcombine < %s | FileCheck %s
+
+%struct.Big = type { [1024 x i32] }
+
+ at x = constant { <{ i32, [1023 x i32] }> } { <{ i32, [1023 x i32] }> <{ i32 1, [1023 x i32] zeroinitializer }> }, align 4
+
+define void @bar() {
+; CHECK-LABEL: @bar(
+; CHECK-NEXT:    call void @foo(ptr nocapture noundef nonnull readonly @x)
+; CHECK-NEXT:    ret void
+;
+  %1 = alloca %struct.Big, align 4
+  call void @llvm.memcpy.p0.p0.i64(ptr noundef nonnull align 4 dereferenceable(4096) %1, ptr noundef nonnull align 4 dereferenceable(4096) @x, i64 4096, i1 false)
+  call void @foo(ptr noundef nonnull nocapture readonly %1) #4
+  ret void
+}
+
+declare void @llvm.memcpy.p0.p0.i64(ptr noalias nocapture writeonly, ptr noalias nocapture readonly, i64, i1 immarg)
+
+declare void @foo(ptr noundef nocapture readonly)
Index: llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
@@ -39,8 +39,8 @@
 /// the alloca, and if the source pointer is a pointer to a constant global, we
 /// can optimize this.
 static bool
-isOnlyCopiedFromConstantMemory(AAResults *AA,
-                               Value *V, MemTransferInst *&TheCopy,
+isOnlyCopiedFromConstantMemory(AAResults *AA, AllocaInst *V,
+                               MemTransferInst *&TheCopy,
                                SmallVectorImpl<Instruction *> &ToDelete) {
   // We track lifetime intrinsics as we encounter them.  If we decide to go
   // ahead and replace the value with the global, this lets the caller quickly
@@ -85,11 +85,12 @@
         if (IsArgOperand && Call->isInAllocaArgument(DataOpNo))
           return false;
 
-        // If this is a readonly/readnone call site, then we know it is just a
-        // load (but one that potentially returns the value itself), so we can
+        // If this call site doesn't modify the memory, then we know it is just
+        // a load (but one that potentially returns the value itself), so we can
         // ignore it if we know that the value isn't captured.
-        if (Call->onlyReadsMemory() &&
-            (Call->use_empty() || Call->doesNotCapture(DataOpNo)))
+        bool CapturesArg = !Call->doesNotCapture(DataOpNo);
+        if ((Call->onlyReadsMemory() && (Call->use_empty() || !CapturesArg)) ||
+            (IsArgOperand && Call->onlyReadsMemory(DataOpNo) && !CapturesArg))
           continue;
 
         // If this is being passed as a byval argument, the caller is making a


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D136822.471270.patch
Type: text/x-patch
Size: 3023 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20221027/ced4e0b4/attachment.bin>