[PATCH] D135886: [MemCpyOpt] Move lifetime marker before call to enable call slot optimization

[Nikita Popov via Phabricator via llvm-commits]

This revision was landed with ongoing or failed builds.
This revision was automatically updated to reflect the committed changes.
Closed by commit rG9a45e4beede2: [MemCpyOpt] Move lifetime marker before call to enable call slot optimization (authored by nikic).

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D135886/new/

https://reviews.llvm.org/D135886

Files:
  llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
  llvm/test/Transforms/MemCpyOpt/lifetime.ll


Index: llvm/test/Transforms/MemCpyOpt/lifetime.ll
===================================================================
--- llvm/test/Transforms/MemCpyOpt/lifetime.ll
+++ llvm/test/Transforms/MemCpyOpt/lifetime.ll
@@ -55,9 +55,8 @@
 ; CHECK-LABEL: @call_slot_move_lifetime_start(
 ; CHECK-NEXT:    [[TMP:%.*]] = alloca i32, align 4
 ; CHECK-NEXT:    [[DST:%.*]] = alloca i32, align 4
-; CHECK-NEXT:    call void @call(ptr [[TMP]])
 ; CHECK-NEXT:    call void @llvm.lifetime.start.p0(i64 4, ptr [[DST]])
-; CHECK-NEXT:    call void @llvm.memcpy.p0.p0.i64(ptr align 4 [[DST]], ptr align 4 [[TMP]], i64 4, i1 false)
+; CHECK-NEXT:    call void @call(ptr [[DST]])
 ; CHECK-NEXT:    call void @llvm.lifetime.end.p0(i64 4, ptr [[DST]])
 ; CHECK-NEXT:    [[V:%.*]] = load i32, ptr [[DST]], align 4
 ; CHECK-NEXT:    ret i32 [[V]]
Index: llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
+++ llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
@@ -331,16 +331,27 @@
 }
 
 // Check for mod or ref of Loc between Start and End, excluding both boundaries.
-// Start and End must be in the same block
+// Start and End must be in the same block.
+// If SkippedLifetimeStart is provided, skip over one clobbering lifetime.start
+// intrinsic and store it inside SkippedLifetimeStart.
 static bool accessedBetween(AliasAnalysis &AA, MemoryLocation Loc,
                             const MemoryUseOrDef *Start,
-                            const MemoryUseOrDef *End) {
+                            const MemoryUseOrDef *End,
+                            Instruction **SkippedLifetimeStart = nullptr) {
   assert(Start->getBlock() == End->getBlock() && "Only local supported");
   for (const MemoryAccess &MA :
        make_range(++Start->getIterator(), End->getIterator())) {
-    if (isModOrRefSet(AA.getModRefInfo(cast<MemoryUseOrDef>(MA).getMemoryInst(),
-                                       Loc)))
+    Instruction *I = cast<MemoryUseOrDef>(MA).getMemoryInst();
+    if (isModOrRefSet(AA.getModRefInfo(I, Loc))) {
+      auto *II = dyn_cast<IntrinsicInst>(I);
+      if (II && II->getIntrinsicID() == Intrinsic::lifetime_start &&
+          SkippedLifetimeStart && !*SkippedLifetimeStart) {
+        *SkippedLifetimeStart = I;
+        continue;
+      }
+
       return true;
+    }
   }
   return false;
 }
@@ -913,8 +924,9 @@
 
   // Check that nothing touches the dest of the copy between
   // the call and the store/memcpy.
+  Instruction *SkippedLifetimeStart = nullptr;
   if (accessedBetween(*AA, DestLoc, MSSA->getMemoryAccess(C),
-                      MSSA->getMemoryAccess(cpyStore))) {
+                      MSSA->getMemoryAccess(cpyStore), &SkippedLifetimeStart)) {
     LLVM_DEBUG(dbgs() << "Call Slot: Dest pointer modified after call\n");
     return false;
   }
@@ -1094,6 +1106,12 @@
     cast<AllocaInst>(cpyDest)->setAlignment(srcAlign);
   }
 
+  if (SkippedLifetimeStart) {
+    SkippedLifetimeStart->moveBefore(C);
+    MSSAU->moveBefore(MSSA->getMemoryAccess(SkippedLifetimeStart),
+                      MSSA->getMemoryAccess(C));
+  }
+
   // Update AA metadata
   // FIXME: MD_tbaa_struct and MD_mem_parallel_loop_access should also be
   // handled here, but combineMetadata doesn't support them yet


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