[llvm] 5f53182 - [LSR] Do not consider uses in lifetime intrinsics (#149492)

[via llvm-commits]

Author: Nikita Popov
Date: 2025-07-18T16:13:00+02:00
New Revision: 5f531827a4b90f6e0051056fffd8642ae1c677e6

URL: https://github.com/llvm/llvm-project/commit/5f531827a4b90f6e0051056fffd8642ae1c677e6
DIFF: https://github.com/llvm/llvm-project/commit/5f531827a4b90f6e0051056fffd8642ae1c677e6.diff

LOG: [LSR] Do not consider uses in lifetime intrinsics (#149492)

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.

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

Modified: 
    llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp b/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
index 636bd81ce0755..9e318b04c2c99 100644
--- a/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
+++ b/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;

diff  --git a/llvm/test/Transforms/LoopStrengthReduce/X86/lifetime-use.ll b/llvm/test/Transforms/LoopStrengthReduce/X86/lifetime-use.ll
new file mode 100644
index 0000000000000..c7a0de22b200b
--- /dev/null
+++ b/llvm/test/Transforms/LoopStrengthReduce/X86/lifetime-use.ll
@@ -0,0 +1,59 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -S -passes=loop-reduce -mtriple=x86_64-unknown-linux-gnu < %s | FileCheck %s
+
+define void @test(ptr %p, i64 %idx) {
+; CHECK-LABEL: define void @test(
+; CHECK-SAME: ptr [[P:%.*]], i64 [[IDX:%.*]]) {
+; CHECK-NEXT:  [[ENTRY:.*]]:
+; CHECK-NEXT:    [[ALLOCA:%.*]] = alloca [4 x [4 x i32]], align 16
+; 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
+; CHECK-NEXT:    [[SCEVGEP:%.*]] = getelementptr i8, ptr [[P]], i64 [[TMP1]]
+; CHECK-NEXT:    [[SCEVGEP3:%.*]] = getelementptr nuw i8, ptr [[ALLOCA]], i64 48
+; CHECK-NEXT:    br label %[[LOOP:.*]]
+; CHECK:       [[LOOP]]:
+; CHECK-NEXT:    [[LSR_IV:%.*]] = phi i64 [ [[LSR_IV_NEXT:%.*]], %[[LOOP]] ], [ -8, %[[ENTRY]] ]
+; CHECK-NEXT:    [[TMP2:%.*]] = shl nsw i64 [[LSR_IV]], 2
+; CHECK-NEXT:    [[SCEVGEP8:%.*]] = getelementptr i8, ptr [[P]], i64 [[TMP2]]
+; CHECK-NEXT:    [[SCEVGEP9:%.*]] = getelementptr i8, ptr [[SCEVGEP8]], i64 32
+; CHECK-NEXT:    [[TMP3:%.*]] = load i32, ptr [[SCEVGEP9]], align 4
+; CHECK-NEXT:    [[SCEVGEP6:%.*]] = getelementptr i8, ptr [[P]], i64 [[LSR_IV]]
+; CHECK-NEXT:    [[SCEVGEP7:%.*]] = getelementptr i8, ptr [[SCEVGEP6]], i64 8
+; CHECK-NEXT:    [[TMP4:%.*]] = load i32, ptr [[SCEVGEP7]], align 4
+; CHECK-NEXT:    [[SCEVGEP4:%.*]] = getelementptr i8, ptr [[SCEVGEP3]], i64 [[LSR_IV]]
+; CHECK-NEXT:    [[SCEVGEP5:%.*]] = getelementptr i8, ptr [[SCEVGEP4]], i64 8
+; CHECK-NEXT:    [[TMP5:%.*]] = load i32, ptr [[SCEVGEP5]], align 4
+; CHECK-NEXT:    [[SCEVGEP1:%.*]] = getelementptr i8, ptr [[SCEVGEP]], i64 [[LSR_IV]]
+; CHECK-NEXT:    [[SCEVGEP2:%.*]] = getelementptr i8, ptr [[SCEVGEP1]], i64 8
+; CHECK-NEXT:    [[TMP6:%.*]] = load i32, ptr [[SCEVGEP2]], align 4
+; CHECK-NEXT:    [[LSR_IV_NEXT]] = add nsw i64 [[LSR_IV]], 4
+; 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 [[ALLOCA]])
+; CHECK-NEXT:    ret void
+;
+entry:
+  %alloca = alloca [4 x [4 x i32]], align 16
+  call void @llvm.lifetime.start.p0(i64 64, ptr %alloca)
+  br label %loop
+
+loop:
+  %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %loop ]
+  %gep1 = getelementptr [4 x [12 x [4 x [4 x i32]]]], ptr %p, i64 0, i64 0, i64 0, i64 %indvars.iv, i64 0
+  %0 = load i32, ptr %gep1, align 4
+  %gep2 = getelementptr [6 x [4 x [4 x i32]]], ptr %p, i64 0, i64 0, i64 0, i64 %indvars.iv
+  %1 = load i32, ptr %gep2, align 4
+  %gep3 = getelementptr [4 x [4 x i32]], ptr %alloca, i64 0, i64 3, i64 %indvars.iv
+  %2 = load i32, ptr %gep3, align 4
+  %gep4 = getelementptr [6 x [4 x [4 x i32]]], ptr %p, i64 0, i64 %idx, i64 3, i64 %indvars.iv
+  %3 = load i32, ptr %gep4, align 4
+  %indvars.iv.next = add i64 %indvars.iv, 1
+  %exitcond.not = icmp eq i64 %indvars.iv, 1
+  br i1 %exitcond.not, label %exit, label %loop
+
+exit:
+  call void @llvm.lifetime.end.p0(i64 64, ptr %alloca)
+  ret void
+}