[llvm-branch-commits] [llvm] release/23.x: [LoopUnroll] Invalidate SCEV after full unrolling (#208874) (PR #210003)

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llvmorg-github-actions[bot] wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: llvmbot

<details>
<summary>Changes</summary>

Backport 42c2980c7c632d7a45776d3e2c51627100f6e763

Requested by: @<!-- -->nikic

---
Full diff: https://github.com/llvm/llvm-project/pull/210003.diff


2 Files Affected:

- (modified) llvm/lib/Transforms/Utils/LoopUnroll.cpp (+4) 
- (added) llvm/test/Transforms/LoopUnroll/full-unroll-scev-invalidation.ll (+55) 


``````````diff
diff --git a/llvm/lib/Transforms/Utils/LoopUnroll.cpp b/llvm/lib/Transforms/Utils/LoopUnroll.cpp
index d00de52e1cb0b..1f9f340a9cb31 100644
--- a/llvm/lib/Transforms/Utils/LoopUnroll.cpp
+++ b/llvm/lib/Transforms/Utils/LoopUnroll.cpp
@@ -1284,6 +1284,10 @@ llvm::UnrollLoop(Loop *L, UnrollLoopOptions ULO, LoopInfo *LI,
   // Loop over the PHI nodes in the original block, setting incoming values.
   for (PHINode *PN : OrigPHINode) {
     if (CompletelyUnroll) {
+      // The RAUW below disconnects the original PHI from its users.
+      // Invalidate cached SCEVs while the def-use chain is still intact.
+      if (SE)
+        SE->forgetValue(PN);
       PN->replaceAllUsesWith(PN->getIncomingValueForBlock(Preheader));
       PN->eraseFromParent();
     } else if (ULO.Count > 1) {
diff --git a/llvm/test/Transforms/LoopUnroll/full-unroll-scev-invalidation.ll b/llvm/test/Transforms/LoopUnroll/full-unroll-scev-invalidation.ll
new file mode 100644
index 0000000000000..a9f7a1df0328a
--- /dev/null
+++ b/llvm/test/Transforms/LoopUnroll/full-unroll-scev-invalidation.ll
@@ -0,0 +1,55 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 6
+; RUN: opt -S -passes='loop(indvars,loop-unroll-full)' %s | FileCheck %s
+
+ at __chk = external global i64
+
+define void @f4(i64 %0) {
+; CHECK-LABEL: define void @f4(
+; CHECK-SAME: i64 [[TMP0:%.*]]) {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    br label %[[LBL_B5:.*]]
+; CHECK:       [[LBL_B5]]:
+; CHECK-NEXT:    br label %[[LBL_B10:.*]]
+; CHECK:       [[LBL_B10]]:
+; CHECK-NEXT:    [[CONV1:%.*]] = trunc i64 [[TMP0]] to i32
+; CHECK-NEXT:    [[TMP1:%.*]] = call i32 @llvm.ctpop.i32(i32 [[CONV1]])
+; CHECK-NEXT:    [[TOBOOL4_NOT:%.*]] = icmp eq i32 [[TMP1]], 0
+; CHECK-NEXT:    br i1 [[TOBOOL4_NOT]], label %[[COMMON_RET1:.*]], label %[[IF_THEN8:.*]]
+; CHECK:       [[IF_THEN8]]:
+; CHECK-NEXT:    store i64 5, ptr @__chk, align 4
+; CHECK-NEXT:    ret void
+; CHECK:       [[COMMON_RET1]]:
+; CHECK-NEXT:    ret void
+;
+entry:
+  br label %lbl_b5
+
+lbl_b5:
+  br label %lbl_b10
+
+lbl_b10:
+  %1 = phi i8 [ 0, %lbl_b5 ], [ 1, %lbl_b10 ]
+  %2 = phi i64 [ %0, %lbl_b5 ], [ 0, %lbl_b10 ]
+  %bb13.1 = phi i32 [ 0, %lbl_b5 ], [ %3, %lbl_b10 ]
+  %conv1 = trunc i64 %2 to i32
+  %3 = call i32 @llvm.ctpop.i32(i32 %conv1)
+  %loadedv = trunc i8 %1 to i1
+  br i1 %loadedv, label %if.then3, label %lbl_b10
+
+if.then3:
+  %tobool4.not = icmp eq i32 %bb13.1, 0
+  br i1 %tobool4.not, label %common.ret, label %if.then8
+
+if.then8:
+  br i1 true, label %if.then10, label %lbl_b5
+
+common.ret:
+  ret void
+
+if.then10:
+  %.lcssa.lcssa34 = phi i32 [ %3, %if.then8 ]
+  store i64 5, ptr @__chk
+  ret void
+}
+
+declare i32 @llvm.ctpop.i32(i32)

``````````

</details>


https://github.com/llvm/llvm-project/pull/210003