[llvm] [LVI] Handle constant value lattice in `getEdgeValueLocal` (PR #161410)

[Yingwei Zheng via llvm-commits]

https://github.com/dtcxzyw created https://github.com/llvm/llvm-project/pull/161410

Closes https://github.com/llvm/llvm-project/issues/161367.

In https://github.com/llvm/llvm-project/pull/157614, we ignored cases where OpLatticeVal might be a constant or notconstant. Directly returning the result causes a type mismatch. I apologize for the oversight in the previous code review.

This patch applies the cast op to constants. For notconstant value lattices, I'd leave it as a todo (it is similar to the constant case, except for trunc without nsw/nuw).


>From 96eae46333b09941749d7095f80faa675dd577d8 Mon Sep 17 00:00:00 2001
From: Yingwei Zheng <dtcxzyw2333 at gmail.com>
Date: Wed, 1 Oct 2025 01:29:17 +0800
Subject: [PATCH] [LVI] Handle constant value lattice in `getEdgeValueLocal`

---
 llvm/lib/Analysis/LazyValueInfo.cpp           | 28 ++++++++++-------
 .../CorrelatedValuePropagation/pr161367.ll    | 31 +++++++++++++++++++
 2 files changed, 48 insertions(+), 11 deletions(-)
 create mode 100644 llvm/test/Transforms/CorrelatedValuePropagation/pr161367.ll

diff --git a/llvm/lib/Analysis/LazyValueInfo.cpp b/llvm/lib/Analysis/LazyValueInfo.cpp
index 6fb28072afe46..0e5bc481383a0 100644
--- a/llvm/lib/Analysis/LazyValueInfo.cpp
+++ b/llvm/lib/Analysis/LazyValueInfo.cpp
@@ -1632,19 +1632,25 @@ LazyValueInfoImpl::getEdgeValueLocal(Value *Val, BasicBlock *BBFrom,
                 *getValueFromCondition(Usr->getOperand(0), Condition,
                                        isTrueDest, /*UseBlockValue*/ false);
 
-            if (!OpLatticeVal.isConstantRange())
-              return OpLatticeVal;
+            if (OpLatticeVal.isConstantRange()) {
+              const unsigned ResultBitWidth =
+                  Usr->getType()->getScalarSizeInBits();
+              if (auto *Trunc = dyn_cast<TruncInst>(Usr))
+                return ValueLatticeElement::getRange(
+                    OpLatticeVal.getConstantRange().truncate(
+                        ResultBitWidth, Trunc->getNoWrapKind()));
 
-            const unsigned ResultBitWidth =
-                Usr->getType()->getScalarSizeInBits();
-            if (auto *Trunc = dyn_cast<TruncInst>(Usr))
               return ValueLatticeElement::getRange(
-                  OpLatticeVal.getConstantRange().truncate(
-                      ResultBitWidth, Trunc->getNoWrapKind()));
-
-            return ValueLatticeElement::getRange(
-                OpLatticeVal.getConstantRange().castOp(
-                    cast<CastInst>(Usr)->getOpcode(), ResultBitWidth));
+                  OpLatticeVal.getConstantRange().castOp(
+                      cast<CastInst>(Usr)->getOpcode(), ResultBitWidth));
+            }
+            if (OpLatticeVal.isConstant()) {
+              Constant *C = OpLatticeVal.getConstant();
+              if (auto *CastC = ConstantFoldCastOperand(
+                      cast<CastInst>(Usr)->getOpcode(), C, Usr->getType(), DL))
+                return ValueLatticeElement::get(CastC);
+            }
+            return ValueLatticeElement::getOverdefined();
           } else {
             // If one of Val's operand has an inferred value, we may be able to
             // infer the value of Val.
diff --git a/llvm/test/Transforms/CorrelatedValuePropagation/pr161367.ll b/llvm/test/Transforms/CorrelatedValuePropagation/pr161367.ll
new file mode 100644
index 0000000000000..346eaeaec72c1
--- /dev/null
+++ b/llvm/test/Transforms/CorrelatedValuePropagation/pr161367.ll
@@ -0,0 +1,31 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 6
+; RUN: opt < %s -passes=correlated-propagation -S | FileCheck %s
+
+; Make sure that we apply trunc to the edge value of %x.
+ at g = external global i8
+
+define i16 @pr161367(i64 %x) {
+; CHECK-LABEL: define i16 @pr161367(
+; CHECK-SAME: i64 [[X:%.*]]) {
+; CHECK-NEXT:  [[ENTRY:.*]]:
+; CHECK-NEXT:    [[TRUNC:%.*]] = trunc i64 [[X]] to i16
+; CHECK-NEXT:    [[EXITCOND:%.*]] = icmp eq i64 [[X]], sub (i64 0, i64 ptrtoint (ptr @g to i64))
+; CHECK-NEXT:    br i1 [[EXITCOND]], label %[[EXIT:.*]], label %[[ELSE:.*]]
+; CHECK:       [[ELSE]]:
+; CHECK-NEXT:    br label %[[EXIT]]
+; CHECK:       [[EXIT]]:
+; CHECK-NEXT:    [[RET:%.*]] = phi i16 [ trunc (i64 sub (i64 0, i64 ptrtoint (ptr @g to i64)) to i16), %[[ENTRY]] ], [ 0, %[[ELSE]] ]
+; CHECK-NEXT:    ret i16 [[RET]]
+;
+entry:
+  %trunc = trunc i64 %x to i16
+  %exitcond = icmp eq i64 %x, sub (i64 0, i64 ptrtoint (ptr @g to i64))
+  br i1 %exitcond, label %exit, label %else
+
+else:
+  br label %exit
+
+exit:
+  %ret = phi i16 [ %trunc, %entry ], [ 0, %else ]
+  ret i16 %ret
+}