review

Author: vtjnash

llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp

@@ -1140,10 +1140,11 @@ bool MemCpyOptPass::processMemCpyMemCpyDependence(MemCpyInst *M,
   if (MForwardOffset != 0 || MDep->getLength() != CopyLength) {
     auto *MDepLen = dyn_cast<ConstantInt>(MDep->getLength());
     auto *MLen = dyn_cast<ConstantInt>(CopyLength);
-    if (!MDepLen || !MLen)
-      return false; // This could be converted to a runtime test (%CopyLength =
+      // This could be converted to a runtime test (%CopyLength =
                     // min(max(0, MDepLen - MForwardOffset), MLen)), but it is
                     // unclear if that is useful
+    if (!MDepLen || !MLen)
+                     return false;
     if (MDepLen->getZExtValue() < MLen->getZExtValue() + MForwardOffset) {
       if (!overreadUndefContents(MSSA, M, MDep, BAA))
         return false;
@@ -1172,7 +1173,7 @@ bool MemCpyOptPass::processMemCpyMemCpyDependence(MemCpyInst *M,
   auto MCopyLoc = MemoryLocation::getForSource(MDep);
   // Truncate the size of the MDep access to just the bytes read
   if (MDep->getLength() != CopyLength) {
-    auto ConstLength = cast<ConstantInt>(CopyLength);
+    auto *ConstLength = cast<ConstantInt>(CopyLength);
     MCopyLoc = MCopyLoc.getWithNewSize(
         LocationSize::precise(ConstLength->getZExtValue()));
   }

llvm/test/Transforms/MemCpyOpt/memcpy-memcpy-offset.ll

@@ -134,7 +134,7 @@ define void @forward_offset_memcpy_inline(ptr %src, ptr %dest) {
   ret void
 }
 
-; We cannot forward `memcpy` because it exceeds the size of `memcpy` it depends on.
+; We can forward `memcpy` by shrinking it to the size of the `memcpy` it depends on.
 define void @forward_oversize_offset(ptr %src, ptr %dest) {
 ; CHECK-LABEL: define void @forward_oversize_offset(
 ; CHECK-SAME: ptr [[SRC:%.*]], ptr [[DEST:%.*]]) {
@@ -218,14 +218,14 @@ define void @pr98675(ptr noalias %p1, ptr noalias %p2) {
 define void @over_offset_cpy(ptr %src) {
 ; CHECK-LABEL: define void @over_offset_cpy(
 ; CHECK-SAME: ptr [[SRC:%.*]]) {
-; CHECK-NEXT:    [[TMP:%.*]] = alloca i8, i64 2, align 1
-; CHECK-NEXT:    [[DST:%.*]] = alloca i8, i64 1, align 1
+; CHECK-NEXT:    [[TMP:%.*]] = alloca [2 x i8], align 1
+; CHECK-NEXT:    [[DST:%.*]] = alloca i8, align 1
 ; CHECK-NEXT:    call void @llvm.memcpy.p0.p0.i64(ptr align 8 [[TMP]], ptr align 8 [[SRC]], i64 1, i1 false)
 ; CHECK-NEXT:    [[TMP_OFFSET:%.*]] = getelementptr inbounds i8, ptr [[TMP]], i64 1
 ; CHECK-NEXT:    ret void
 ;
-  %tmp = alloca i8, i64 2
-  %dst = alloca i8, i64 1
+  %tmp = alloca [2 x i8]
+  %dst = alloca i8
   call void @llvm.memcpy.p0.p0.i64(ptr align 8 %tmp, ptr align 8 %src, i64 1, i1 false)
   %tmp_offset = getelementptr inbounds i8, ptr %tmp, i64 1
   call void @llvm.memcpy.p0.p0.i64(ptr align 8 %dst, ptr align 8 %tmp_offset, i64 1, i1 false)