[PATCH] D87134: [SelectionDAG] memcpy expansion of const volatile struct ignores const zero

[Simon Wallis via Phabricator via llvm-commits]

simonwallis2 created this revision.
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In getMemcpyLoadsAndStores(), a memcpy where the source is a zero constant is expanded to a MemOp::Set instead of a MemOp::Copy, even when the memcpy is volatile.
This is incorrect.

The fix is to add a check for volatile, and expand to MemOp::Copy in the volatile case.


https://reviews.llvm.org/D87134

Files:
  llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
  llvm/test/CodeGen/ARM/memcpy-const-vol-struct.ll


Index: llvm/test/CodeGen/ARM/memcpy-const-vol-struct.ll
===================================================================
--- /dev/null
+++ llvm/test/CodeGen/ARM/memcpy-const-vol-struct.ll
@@ -0,0 +1,18 @@
+; RUN: llc -mtriple=armv7-arm-none-eabi -o - %s | FileCheck %s
+
+%struct.sMyType = type { i32 }
+
+ at val = hidden constant %struct.sMyType zeroinitializer, align 4
+ at v = internal global %struct.sMyType zeroinitializer, align 4
+
+define hidden void @InitVal() local_unnamed_addr {
+entry:
+  call void @llvm.memcpy.p0i8.p0i8.i32(i8* align 4 bitcast (%struct.sMyType* @v to i8*), i8* align 4 bitcast (%struct.sMyType* @val to i8*), i32 4, i1 true)
+; The last argument is the isvolatile argument. This is a volatile memcpy.
+; Test that the memcpy expansion does not optimize away the load.
+; CHECK: ldr
+; CHECK: str
+  ret void
+}
+
+declare void @llvm.memcpy.p0i8.p0i8.i32(i8* noalias nocapture writeonly, i8* noalias nocapture readonly, i32, i1 immarg)
Index: llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
===================================================================
--- llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -6052,7 +6052,8 @@
     SrcAlign = Alignment;
   assert(SrcAlign && "SrcAlign must be set");
   ConstantDataArraySlice Slice;
-  bool CopyFromConstant = isMemSrcFromConstant(Src, Slice);
+  // If marked as volatile, perform a copy even when marked as constant.
+  bool CopyFromConstant = !isVol && isMemSrcFromConstant(Src, Slice);
   bool isZeroConstant = CopyFromConstant && Slice.Array == nullptr;
   unsigned Limit = AlwaysInline ? ~0U : TLI.getMaxStoresPerMemcpy(OptSize);
   const MemOp Op = isZeroConstant


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