[llvm] [LoopVectorize] Remove redundant code in emitSCEVChecks (PR #111132)

[David Sherwood via llvm-commits]

https://github.com/david-arm created https://github.com/llvm/llvm-project/pull/111132

There was some code in emitSCEVChecks to update the dominator
tree if LoopBypassBlocks is empty, however there are no tests
that fail when replacing this code with an assert. I built
both SPEC2017 and the LLVM test suite and also didn't see any
build failures. I've removed the code for now and added an
assert to guard this in case anything changes, since it seems
pointless to have code that's impossible to defend.

>From f6fa81aae8d489fb2b70ee54b7f078d6b95cf11f Mon Sep 17 00:00:00 2001
From: David Sherwood <david.sherwood at arm.com>
Date: Fri, 4 Oct 2024 10:47:33 +0000
Subject: [PATCH] [LoopVectorize] Remove redundant code in emitSCEVChecks

There was some code in emitSCEVChecks to update the dominator
tree if LoopBypassBlocks is empty, however there are no tests
that fail when replacing this code with an assert. I built
both SPEC2017 and the LLVM test suite and also didn't see any
build failures. I've removed the code for now and added an
assert to guard this in case anything changes, since it seems
pointless to have code that's impossible to defend.
---
 llvm/lib/Transforms/Vectorize/LoopVectorize.cpp | 14 ++------------
 1 file changed, 2 insertions(+), 12 deletions(-)

diff --git a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
index de3b981a4fe390..7c7d6693a1dccd 100644
--- a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -2486,18 +2486,8 @@ BasicBlock *InnerLoopVectorizer::emitSCEVChecks(BasicBlock *Bypass) {
            (OptForSizeBasedOnProfile &&
             Cost->Hints->getForce() != LoopVectorizeHints::FK_Enabled)) &&
          "Cannot SCEV check stride or overflow when optimizing for size");
-
-
-  // Update dominator only if this is first RT check.
-  if (LoopBypassBlocks.empty()) {
-    DT->changeImmediateDominator(Bypass, SCEVCheckBlock);
-    if (!Cost->requiresScalarEpilogue(VF.isVector()))
-      // If there is an epilogue which must run, there's no edge from the
-      // middle block to exit blocks  and thus no need to update the immediate
-      // dominator of the exit blocks.
-      DT->changeImmediateDominator(LoopExitBlock, SCEVCheckBlock);
-  }
-
+  assert(!LoopBypassBlocks.empty() &&
+         "Should already be a bypass block due to iteration count check");
   LoopBypassBlocks.push_back(SCEVCheckBlock);
   AddedSafetyChecks = true;
   return SCEVCheckBlock;