[llvm] [InstCombine] add control for SimplifyDemandedVectorElts depth limit (PR #113717)

[Princeton Ferro via llvm-commits]

https://github.com/Prince781 created https://github.com/llvm/llvm-project/pull/113717

Allows customizing the depth of the recursive search on vectors that InstCombine does when looking for unused elements.

We find it helpful to be able to customize this for compile time reasons.

>From 98e6e97b774620f27a053bb0885f94c716753464 Mon Sep 17 00:00:00 2001
From: Princeton Ferro <pferro at nvidia.com>
Date: Thu, 3 Oct 2024 14:35:36 -0700
Subject: [PATCH] [InstCombine] add control for SimplifyDemandedVectorElts
 depth limit

Allows customizing the depth of the recursive search on vectors that
InstCombine does when looking for unused elements.
---
 .../InstCombine/InstCombineSimplifyDemanded.cpp           | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
index 8ca705ae1d364d..5eb807dcb76cef 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
@@ -30,6 +30,12 @@ static cl::opt<bool>
                              "SimplifyDemandedBits() are consistent"),
                     cl::Hidden, cl::init(false));
 
+static cl::opt<unsigned> SimplifyDemandedVectorEltsDepthLimit(
+    "instcombine-simplify-vector-elts-depth",
+    cl::desc(
+        "Depth limit when simplifying vector instructions and their operands"),
+    cl::Hidden, cl::init(10));
+
 /// Check to see if the specified operand of the specified instruction is a
 /// constant integer. If so, check to see if there are any bits set in the
 /// constant that are not demanded. If so, shrink the constant and return true.
@@ -1432,7 +1438,7 @@ Value *InstCombinerImpl::SimplifyDemandedVectorElts(Value *V,
   }
 
   // Limit search depth.
-  if (Depth == 10)
+  if (Depth == SimplifyDemandedVectorEltsDepthLimit)
     return nullptr;
 
   if (!AllowMultipleUsers) {