release/20.x: [ScalarEvolution] Handle addrec incoming value in isImpliedViaMerge() (#126236)

[llvmbot]

Backport ae08969 7aed53e

Requested by: @nikic

[llvmbot]

@dtcxzyw What do you think about merging this PR to the release branch?

[llvmbot]

@llvm/pr-subscribers-llvm-transforms

@llvm/pr-subscribers-llvm-analysis

Author: None (llvmbot)

Changes

Backport ae08969 7aed53e

Requested by: @nikic

---

Full diff: https://github.com/llvm/llvm-project/pull/126492.diff

2 Files Affected:

• (modified) llvm/lib/Analysis/ScalarEvolution.cpp (+6)
• (added) llvm/test/Transforms/IndVarSimplify/pr126012.ll (+53)

diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 2ce40877b523e10..c71202c8dd58e4d 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -12402,6 +12402,12 @@ bool ScalarEvolution::isImpliedViaMerge(CmpPredicate Pred, const SCEV *LHS,
       // iteration of a loop.
       if (!properlyDominates(L, LBB))
         return false;
+      // Addrecs are considered to properly dominate their loop, so are missed
+      // by the previous check. Discard any values that have computable
+      // evolution in this loop.
+      if (auto *Loop = LI.getLoopFor(LBB))
+        if (hasComputableLoopEvolution(L, Loop))
+          return false;
       if (!ProvedEasily(L, RHS))
         return false;
     }
diff --git a/llvm/test/Transforms/IndVarSimplify/pr126012.ll b/llvm/test/Transforms/IndVarSimplify/pr126012.ll
new file mode 100644
index 000000000000000..5189fe020dd3bfd
--- /dev/null
+++ b/llvm/test/Transforms/IndVarSimplify/pr126012.ll
@@ -0,0 +1,53 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -S -passes=indvars < %s | FileCheck %s
+
+; Do not infer that %cmp is true. The %indvar3 input of %indvar2 comes from
+; a previous iteration, so we should not compare it to a value from the current
+; iteration.
+define i32 @test() {
+; CHECK-LABEL: define i32 @test() {
+; CHECK-NEXT:  [[ENTRY:.*]]:
+; CHECK-NEXT:    br label %[[FOR_PREHEADER:.*]]
+; CHECK:       [[FOR_PREHEADER]]:
+; CHECK-NEXT:    [[INDVAR1:%.*]] = phi i32 [ 0, %[[ENTRY]] ], [ [[PHI:%.*]], %[[FOR_INC:.*]] ]
+; CHECK-NEXT:    [[INDVAR2:%.*]] = phi i32 [ 1, %[[ENTRY]] ], [ [[INDVAR3:%.*]], %[[FOR_INC]] ]
+; CHECK-NEXT:    [[INDVAR3]] = phi i32 [ 0, %[[ENTRY]] ], [ [[INC:%.*]], %[[FOR_INC]] ]
+; CHECK-NEXT:    [[COND1:%.*]] = icmp eq i32 [[INDVAR3]], 0
+; CHECK-NEXT:    br i1 [[COND1]], label %[[FOR_INC]], label %[[FOR_END:.*]]
+; CHECK:       [[FOR_END]]:
+; CHECK-NEXT:    [[CMP:%.*]] = icmp ugt i32 [[INDVAR2]], 0
+; CHECK-NEXT:    [[EXT:%.*]] = zext i1 [[CMP]] to i32
+; CHECK-NEXT:    br label %[[FOR_INC]]
+; CHECK:       [[FOR_INC]]:
+; CHECK-NEXT:    [[PHI]] = phi i32 [ [[EXT]], %[[FOR_END]] ], [ 0, %[[FOR_PREHEADER]] ]
+; CHECK-NEXT:    [[INC]] = add nuw nsw i32 [[INDVAR3]], 1
+; CHECK-NEXT:    [[EXITCOND:%.*]] = icmp eq i32 [[INDVAR3]], 2
+; CHECK-NEXT:    br i1 [[EXITCOND]], label %[[FOR_EXIT:.*]], label %[[FOR_PREHEADER]]
+; CHECK:       [[FOR_EXIT]]:
+; CHECK-NEXT:    [[INDVAR1_LCSSA:%.*]] = phi i32 [ [[INDVAR1]], %[[FOR_INC]] ]
+; CHECK-NEXT:    ret i32 [[INDVAR1_LCSSA]]
+;
+entry:
+  br label %for.preheader
+
+for.preheader:
+  %indvar1 = phi i32 [ 0, %entry ], [ %phi, %for.inc ]
+  %indvar2 = phi i32 [ 1, %entry ], [ %indvar3, %for.inc ]
+  %indvar3 = phi i32 [ 0, %entry ], [ %inc, %for.inc ]
+  %cond1 = icmp eq i32 %indvar3, 0
+  br i1 %cond1, label %for.inc, label %for.end
+
+for.end:
+  %cmp = icmp sgt i32 %indvar2, 0
+  %ext = zext i1 %cmp to i32
+  br label %for.inc
+
+for.inc:
+  %phi = phi i32 [ %ext, %for.end ], [ 0, %for.preheader ]
+  %inc = add i32 %indvar3, 1
+  %exitcond = icmp eq i32 %indvar3, 2
+  br i1 %exitcond, label %for.exit, label %for.preheader
+
+for.exit:
+  ret i32 %indvar1
+}

[github-actions]

@nikic (or anyone else). If you would like to add a note about this fix in the release notes (completely optional). Please reply to this comment with a one or two sentence description of the fix. When you are done, please add the release:note label to this PR.