[InstCombine] add control for SimplifyDemandedVectorElts depth limit

[Prince781]

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.

[llvmbot]

@llvm/pr-subscribers-llvm-transforms

Author: Princeton Ferro (Prince781)

Changes

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.

---

Full diff: https://github.com/llvm/llvm-project/pull/113717.diff

1 Files Affected:

• (modified) llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp (+7-1)

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) {