[LoopRotate] Use poison instead of undef as placeholder

[pedroclobo]

The poison values are used to substitute debug information of values moved from the original header into the preheader that are no longer available in the former.

[llvmbot]

@llvm/pr-subscribers-debuginfo

@llvm/pr-subscribers-llvm-transforms

Author: Pedro Lobo (pedroclobo)

Changes

The poison values are used to substitute debug information of values moved from the original header into the preheader that are no longer available in the former.

---

Full diff: https://github.com/llvm/llvm-project/pull/119135.diff

2 Files Affected:

• (modified) llvm/lib/Transforms/Utils/LoopRotationUtils.cpp (+4-4)
• (modified) llvm/test/Transforms/LoopRotate/dbgvalue.ll (+3-3)

diff --git a/llvm/lib/Transforms/Utils/LoopRotationUtils.cpp b/llvm/lib/Transforms/Utils/LoopRotationUtils.cpp
index 04042e71a2b82e..fffff295ba926d 100644
--- a/llvm/lib/Transforms/Utils/LoopRotationUtils.cpp
+++ b/llvm/lib/Transforms/Utils/LoopRotationUtils.cpp
@@ -171,14 +171,14 @@ static void RewriteUsesOfClonedInstructions(BasicBlock *OrigHeader,
       // Users in the OrigPreHeader need to use the value to which the
       // original definitions are mapped and anything else can be handled by
       // the SSAUpdater. To avoid adding PHINodes, check if the value is
-      // available in UserBB, if not substitute undef.
+      // available in UserBB, if not substitute poison.
       Value *NewVal;
       if (UserBB == OrigPreheader)
         NewVal = OrigPreHeaderVal;
       else if (SSA.HasValueForBlock(UserBB))
         NewVal = SSA.GetValueInMiddleOfBlock(UserBB);
       else
-        NewVal = UndefValue::get(OrigHeaderVal->getType());
+        NewVal = PoisonValue::get(OrigHeaderVal->getType());
       DbgValue->replaceVariableLocationOp(OrigHeaderVal, NewVal);
     }
 
@@ -194,14 +194,14 @@ static void RewriteUsesOfClonedInstructions(BasicBlock *OrigHeader,
       // Users in the OrigPreHeader need to use the value to which the
       // original definitions are mapped and anything else can be handled by
       // the SSAUpdater. To avoid adding PHINodes, check if the value is
-      // available in UserBB, if not substitute undef.
+      // available in UserBB, if not substitute poison.
       Value *NewVal;
       if (UserBB == OrigPreheader)
         NewVal = OrigPreHeaderVal;
       else if (SSA.HasValueForBlock(UserBB))
         NewVal = SSA.GetValueInMiddleOfBlock(UserBB);
       else
-        NewVal = UndefValue::get(OrigHeaderVal->getType());
+        NewVal = PoisonValue::get(OrigHeaderVal->getType());
       DVR->replaceVariableLocationOp(OrigHeaderVal, NewVal);
     }
   }
diff --git a/llvm/test/Transforms/LoopRotate/dbgvalue.ll b/llvm/test/Transforms/LoopRotate/dbgvalue.ll
index b58d821fbca5d7..026306a4637f0e 100644
--- a/llvm/test/Transforms/LoopRotate/dbgvalue.ll
+++ b/llvm/test/Transforms/LoopRotate/dbgvalue.ll
@@ -113,7 +113,7 @@ return:                                           ; preds = %if.end
 
 ; Check that the dbg.values move up to being immediately below the PHIs,
 ; using their Values. However once we exit the loop, the x and y values
-; become irrelevant and undef, only z gets an LCSSA PHI to preserve it.
+; become irrelevant and poison, only z gets an LCSSA PHI to preserve it.
 ;
 ; Note that while the icmp is initially undominated by any dbg.value and thus
 ; shouldn't get a variable location, the first iteration is peeled off into the
@@ -138,8 +138,8 @@ define i32 @tak2(i32 %x, i32 %y, i32 %z) nounwind ssp !dbg !21 {
 ; CHECK:      tail call i32 @tak(i32
 ; CHECK: if.end:
 ; CHECK-NEXT: z.tr.lcssa = phi i32
-; CHECK-NEXT: #dbg_value(i32 undef
-; CHECK-NEXT: #dbg_value(i32 undef
+; CHECK-NEXT: #dbg_value(i32 poison
+; CHECK-NEXT: #dbg_value(i32 poison
 ; CHECK-NEXT: #dbg_value(i32 %z.tr.lcssa
 entry:
   br label %tailrecurse

[pedroclobo]

cc @nunoplopes