Fix a really bad miscompile introduced in r216865 - the else-if logic

chain became completely broken here as *all* intrinsic users ended up
being skipped, and the ones that seemed to be singled out were actually
the exact wrong set.

This is a great example of why long else-if chains can be easily
confusing. Switch the entire code to use early exits and early continues
to have simpler (and more importantly, correct) logic here, as well as
fixing the reversed logic for detecting and continuing on lifetime
intrinsics.

I've also significantly cleaned up the test case and added another test
case demonstrating an example where the optimization is not (trivially)
safe to perform.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@216871 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/Scalar/MemCpyOptimizer.cpp b/lib/Transforms/Scalar/MemCpyOptimizer.cpp
index b1a2ed3..c750ece 100644 (file)
--- a/lib/Transforms/Scalar/MemCpyOptimizer.cpp
+++ b/lib/Transforms/Scalar/MemCpyOptimizer.cpp
@@ -673,19 +673,23 @@ bool MemCpyOpt::performCallSlotOptzn(Instruction *cpy,
     if (isa<BitCastInst>(U) || isa<AddrSpaceCastInst>(U)) {
       for (User *UU : U->users())
         srcUseList.push_back(UU);
-    } else if (GetElementPtrInst *G = dyn_cast<GetElementPtrInst>(U)) {
-      if (G->hasAllZeroIndices())
-        for (User *UU : U->users())
-          srcUseList.push_back(UU);
-      else
+      continue;
+    }
+    if (GetElementPtrInst *G = dyn_cast<GetElementPtrInst>(U)) {
+      if (!G->hasAllZeroIndices())
         return false;
-    } else if (const IntrinsicInst *IT = dyn_cast<IntrinsicInst>(U)) {
-      if (IT->getIntrinsicID() != Intrinsic::lifetime_start &&
-          IT->getIntrinsicID() != Intrinsic::lifetime_end)
+
+      for (User *UU : U->users())
+        srcUseList.push_back(UU);
+      continue;
+    }
+    if (const IntrinsicInst *IT = dyn_cast<IntrinsicInst>(U))
+      if (IT->getIntrinsicID() == Intrinsic::lifetime_start ||
+          IT->getIntrinsicID() == Intrinsic::lifetime_end)
         continue;
-    } else if (U != C && U != cpy) {
+
+    if (U != C && U != cpy)
       return false;
-    }
   }
 
   // Check that src isn't captured by the called function since the

diff --git a/test/Transforms/MemCpyOpt/memcpy-to-memset-with-lifetimes.ll b/test/Transforms/MemCpyOpt/memcpy-to-memset-with-lifetimes.ll
index d702f3f..6263176 100644 (file)
--- a/test/Transforms/MemCpyOpt/memcpy-to-memset-with-lifetimes.ll
+++ b/test/Transforms/MemCpyOpt/memcpy-to-memset-with-lifetimes.ll
@@ -3,20 +3,47 @@
 target datalayout = "e-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64-unknown-linux-gnu"
 
-define void @foo([8 x i64]* noalias nocapture sret dereferenceable(64)) {
+define void @foo([8 x i64]* noalias nocapture sret dereferenceable(64) %sret) {
 entry-block:
   %a = alloca [8 x i64], align 8
-  %1 = bitcast [8 x i64]* %a to i8*
-  call void @llvm.lifetime.start(i64 64, i8* %1)
-  call void @llvm.memset.p0i8.i64(i8* %1, i8 0, i64 64, i32 8, i1 false)
-  %2 = bitcast [8 x i64]* %0 to i8*
-  call void @llvm.memcpy.p0i8.p0i8.i64(i8* %2, i8* %1, i64 64, i32 8, i1 false)
-  call void @llvm.lifetime.end(i64 64, i8* %1)
+  %a.cast = bitcast [8 x i64]* %a to i8*
+  call void @llvm.lifetime.start(i64 64, i8* %a.cast)
+  call void @llvm.memset.p0i8.i64(i8* %a.cast, i8 0, i64 64, i32 8, i1 false)
+  %sret.cast = bitcast [8 x i64]* %sret to i8*
+  call void @llvm.memcpy.p0i8.p0i8.i64(i8* %sret.cast, i8* %a.cast, i64 64, i32 8, i1 false)
+  call void @llvm.lifetime.end(i64 64, i8* %a.cast)
   ret void
 
 ; CHECK-LABEL: @foo(
-; CHECK: %1 = bitcast
-; CHECK: call void @llvm.memset
+; CHECK:         %[[sret_cast:[^=]+]] = bitcast [8 x i64]* %sret to i8*
+; CHECK-NEXT:    call void @llvm.memset.p0i8.i64(i8* %[[sret_cast]], i8 0, i64 64
+; CHECK-NOT: call void @llvm.memcpy
+; CHECK: ret void
+}
+
+define void @bar([8 x i64]* noalias nocapture sret dereferenceable(64) %sret, [8 x i64]* noalias nocapture dereferenceable(64) %out) {
+entry-block:
+  %a = alloca [8 x i64], align 8
+  %a.cast = bitcast [8 x i64]* %a to i8*
+  call void @llvm.lifetime.start(i64 64, i8* %a.cast)
+  call void @llvm.memset.p0i8.i64(i8* %a.cast, i8 0, i64 64, i32 8, i1 false)
+  %sret.cast = bitcast [8 x i64]* %sret to i8*
+  call void @llvm.memcpy.p0i8.p0i8.i64(i8* %sret.cast, i8* %a.cast, i64 64, i32 8, i1 false)
+  call void @llvm.memset.p0i8.i64(i8* %a.cast, i8 42, i64 32, i32 8, i1 false)
+  %out.cast = bitcast [8 x i64]* %out to i8*
+  call void @llvm.memcpy.p0i8.p0i8.i64(i8* %out.cast, i8* %a.cast, i64 64, i32 8, i1 false)
+  call void @llvm.lifetime.end(i64 64, i8* %a.cast)
+  ret void
+
+; CHECK-LABEL: @bar(
+; CHECK:         %[[a:[^=]+]] = alloca [8 x i64]
+; CHECK:         %[[a_cast:[^=]+]] = bitcast [8 x i64]* %[[a]] to i8*
+; CHECK:         call void @llvm.memset.p0i8.i64(i8* %[[a_cast]], i8 0, i64 64
+; CHECK:         %[[sret_cast:[^=]+]] = bitcast [8 x i64]* %sret to i8*
+; CHECK:         call void @llvm.memcpy.p0i8.p0i8.i64(i8* %[[sret_cast]], i8* %[[a_cast]], i64 64
+; CHECK:         call void @llvm.memset.p0i8.i64(i8* %[[a_cast]], i8 42, i64 32
+; CHECK:         %[[out_cast:[^=]+]] = bitcast [8 x i64]* %out to i8*
+; CHECK:         call void @llvm.memcpy.p0i8.p0i8.i64(i8* %[[out_cast]], i8* %[[a_cast]], i64 64
 ; CHECK-NOT: call void @llvm.memcpy
 ; CHECK: ret void
 }