Lifetimes fix for GenXStructSplitter

Generate lifetime intrinsics only on successfull substitution.
Otherwise they prevent DCE from removing newly added allocas

Author: mshelego

IGC/VectorCompiler/lib/GenXCodeGen/GenXStructSplitter.cpp

@@ -1172,8 +1172,6 @@ Substituter::generateAlloca(AllocaInst &AI,
       NewTy, 0, AI.getName() + "." + getTypePrefix(*getBaseTy(NewTy)));
   NewAI->setAlignment(IGCLLVM::getAlign(AI));
 
-  createLifetime(&AI, NewAI);
-
   DbgDeclareInst *DbgDeclare = getDbgDeclare(AI);
   if (!DbgDeclare)
     return NewAI;
@@ -1459,6 +1457,11 @@ bool Substituter::processAlloca(AllocaInst &Alloca) {
   for (auto &[InstToReplace, ToInst] : InstToInst)
     InstToReplace->replaceAllUsesWith(ToInst);
 
+  for (auto &[Ty, Inst] : NewInstrs) {
+    auto *NewAlloca = cast<AllocaInst>(Inst);
+    createLifetime(&Alloca, NewAlloca);
+  }
+
   return true;
 }
 

IGC/VectorCompiler/test/StructSplitter/lifetime.ll

@@ -25,16 +25,16 @@ entry:
   %f2 = alloca %F, align 4
   %f3 = alloca %F, align 4
 
-; CHECK: %[[BC1:[^ ]+]] = bitcast %F* %f1 to i8*
-; CHECK: %[[BC2:[^ ]+]] = bitcast %F* %f2 to i8*
-; CHECK: %[[BC_I_S:[^ ]+]] = bitcast i32* %[[I_A]] to i8*
-; CHECK: call void @llvm.lifetime.start.p0i8(i64 4, i8* %[[BC_I_S]])
-; CHECK: %[[BC_F_S:[^ ]+]] = bitcast float* %[[F_A]] to i8*
-; CHECK: call void @llvm.lifetime.start.p0i8(i64 4, i8* %[[BC_F_S]])
+; CHECK:     %[[BC1:[^ ]+]] = bitcast %F* %f1 to i8*
+; CHECK:     %[[BC2:[^ ]+]] = bitcast %F* %f2 to i8*
+; CHECK-DAG: %[[BC_I_S:[^ ]+]] = bitcast i32* %[[I_A]] to i8*
+; CHECK-DAG: call void @llvm.lifetime.start.p0i8(i64 4, i8* %[[BC_I_S]])
+; CHECK-DAG: %[[BC_F_S:[^ ]+]] = bitcast float* %[[F_A]] to i8*
+; CHECK-DAG: call void @llvm.lifetime.start.p0i8(i64 4, i8* %[[BC_F_S]])
   %bc1 = bitcast %F* %f1 to i8*
   %bc2 = bitcast %F* %f2 to i8*
-  call void @llvm.lifetime.start.p0i8(i64 1, i8* %bc1)
-  call void @llvm.lifetime.start.p0i8(i64 2, i8* %bc2)
+  call void @llvm.lifetime.start.p0i8(i64 8, i8* %bc1)
+  call void @llvm.lifetime.start.p0i8(i64 8, i8* %bc2)
 
 ; CHECK: %[[I_USAGE:[^ ]+]] = ptrtoint i32* %[[I_A]] to i64
   %i = getelementptr %F, %F* %f1, i32 0, i32 0
@@ -53,12 +53,12 @@ entry:
   %i1 = getelementptr %F, %F* %f3, i32 0, i32 0
   %i1_usage = ptrtoint i32* %i1 to i64            ; %i1 wont be replaced because of addrspacecast.
 
-; CHECK: %[[BC_I_E:[^ ]+]] = bitcast i32* %[[I_A]] to i8*
-; CHECK: call void @llvm.lifetime.end.p0i8(i64 4, i8* %[[BC_I_E]])
-; CHECK: %[[BC_F_E:[^ ]+]] = bitcast float* %[[F_A]] to i8*
-; CHECK: call void @llvm.lifetime.end.p0i8(i64 4, i8* %[[BC_F_E]])
-  call void @llvm.lifetime.end.p0i8(i64 1, i8* %bc1)
-  call void @llvm.lifetime.end.p0i8(i64 2, i8* %bc2)
+; CHECK-DAG: %[[BC_I_E:[^ ]+]] = bitcast i32* %[[I_A]] to i8*
+; CHECK-DAG: call void @llvm.lifetime.end.p0i8(i64 4, i8* %[[BC_I_E]])
+; CHECK-DAG: %[[BC_F_E:[^ ]+]] = bitcast float* %[[F_A]] to i8*
+; CHECK-DAG: call void @llvm.lifetime.end.p0i8(i64 4, i8* %[[BC_F_E]])
+  call void @llvm.lifetime.end.p0i8(i64 8, i8* %bc1)
+  call void @llvm.lifetime.end.p0i8(i64 8, i8* %bc2)
 
   ret void
 }