[LSR] Do not consider uses in lifetime intrinsics

We should ignore uses of pointers in lifetime intrinsics, as these
are not actually materialized in the final code, so don't affect
register pressure or anything else LSR needs to model.

Handling these only results in peculiar rewrites where additional
intermediate GEPs are introduced.

Author: nikic

llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp

@@ -3790,6 +3790,11 @@ LSRInstance::CollectLoopInvariantFixupsAndFormulae() {
             continue;
         }
 
+        // Do not consider uses inside lifetime intrinsics. These are not
+        // actually materialized.
+        if (UserInst->isLifetimeStartOrEnd())
+          continue;
+
         std::pair<size_t, Immediate> P =
             getUse(S, LSRUse::Basic, MemAccessTy());
         size_t LUIdx = P.first;

llvm/test/Transforms/LoopStrengthReduce/X86/lifetime-use.ll

@@ -6,8 +6,6 @@ define void @test(ptr %p, i64 %idx) {
 ; CHECK-SAME: ptr [[P:%.*]], i64 [[IDX:%.*]]) {
 ; CHECK-NEXT:  [[ENTRY:.*]]:
 ; CHECK-NEXT:    [[ALLOCA:%.*]] = alloca [4 x [4 x i32]], align 16
-; CHECK-NEXT:    [[SCEVGEP10:%.*]] = getelementptr nuw i8, ptr [[ALLOCA]], i64 48
-; CHECK-NEXT:    [[SCEVGEP11:%.*]] = getelementptr i8, ptr [[SCEVGEP10]], i64 -48
 ; CHECK-NEXT:    call void @llvm.lifetime.start.p0(i64 64, ptr [[ALLOCA]])
 ; CHECK-NEXT:    [[TMP0:%.*]] = shl i64 [[IDX]], 6
 ; CHECK-NEXT:    [[TMP1:%.*]] = add nuw nsw i64 [[TMP0]], 48
@@ -33,7 +31,7 @@ define void @test(ptr %p, i64 %idx) {
 ; CHECK-NEXT:    [[EXITCOND_NOT:%.*]] = icmp eq i64 [[LSR_IV_NEXT]], 0
 ; CHECK-NEXT:    br i1 [[EXITCOND_NOT]], label %[[EXIT:.*]], label %[[LOOP]]
 ; CHECK:       [[EXIT]]:
-; CHECK-NEXT:    call void @llvm.lifetime.end.p0(i64 64, ptr [[SCEVGEP11]])
+; CHECK-NEXT:    call void @llvm.lifetime.end.p0(i64 64, ptr [[ALLOCA]])
 ; CHECK-NEXT:    ret void
 ;
 entry: