[llvm] [NFC][LoopVectorize] Add more loop early exit asserts (PR #122732)

[David Sherwood via llvm-commits]

https://github.com/david-arm created https://github.com/llvm/llvm-project/pull/122732

This patch is split off #120567, adding asserts in
addScalarResumePhis and addExitUsersForFirstOrderRecurrences
that the loop does not contain an uncountable early exit,
since the code cannot yet handle them correctly.

>From 15da03a554118bc335e281ccefd308a7a89fd2bd Mon Sep 17 00:00:00 2001
From: David Sherwood <david.sherwood at arm.com>
Date: Mon, 13 Jan 2025 15:51:49 +0000
Subject: [PATCH] [NFC][LoopVectorize] Add more loop early exit asserts

This patch is split off #120567, adding asserts in
addScalarResumePhis and addExitUsersForFirstOrderRecurrences
that the loop does not contain an uncountable early exit,
since the code cannot yet handle them correctly.
---
 llvm/lib/Transforms/Vectorize/LoopVectorize.cpp | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
index b017b61a45a0c3..9dc32c773b79a5 100644
--- a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -8925,8 +8925,9 @@ static void addScalarResumePhis(VPRecipeBuilder &Builder, VPlan &Plan) {
   VPTypeAnalysis TypeInfo(Plan.getCanonicalIV()->getScalarType());
   auto *ScalarPH = Plan.getScalarPreheader();
   auto *MiddleVPBB = cast<VPBasicBlock>(ScalarPH->getSinglePredecessor());
+  VPRegionBlock *VectorRegion = Plan.getVectorLoopRegion();
   VPBuilder VectorPHBuilder(
-      cast<VPBasicBlock>(Plan.getVectorLoopRegion()->getSinglePredecessor()));
+      cast<VPBasicBlock>(VectorRegion->getSinglePredecessor()));
   VPBuilder MiddleBuilder(MiddleVPBB, MiddleVPBB->getFirstNonPhi());
   VPBuilder ScalarPHBuilder(ScalarPH);
   VPValue *OneVPV = Plan.getOrAddLiveIn(
@@ -8958,6 +8959,8 @@ static void addScalarResumePhis(VPRecipeBuilder &Builder, VPlan &Plan) {
     // start value provides the value if the loop is bypassed.
     bool IsFOR = isa<VPFirstOrderRecurrencePHIRecipe>(VectorPhiR);
     auto *ResumeFromVectorLoop = VectorPhiR->getBackedgeValue();
+    assert(VectorRegion->getSingleSuccessor() == Plan.getMiddleBlock() &&
+           "Cannot handle loops with uncountable early exits");
     if (IsFOR)
       ResumeFromVectorLoop = MiddleBuilder.createNaryOp(
           VPInstruction::ExtractFromEnd, {ResumeFromVectorLoop, OneVPV}, {},
@@ -9127,6 +9130,9 @@ static void addExitUsersForFirstOrderRecurrences(
     if (!FOR)
       continue;
 
+    assert(VectorRegion->getSingleSuccessor() == Plan.getMiddleBlock() &&
+           "Cannot handle loops with uncountable early exits");
+
     // This is the second phase of vectorizing first-order recurrences, creating
     // extract for users outside the loop. An overview of the transformation is
     // described below. Suppose we have the following loop with some use after