[LV] Enable auto-vectorisation of loops with uncountable exits

Until now the feature to enable vectorisation of some early exit
loops with uncountable exits was controlled under a flag, off by
default. Now that we have efficient code generation for
vectorising such loops (see PR #130766) and we are still far
enough away from the next LLVM release it seems like a good time
to enable the feature by default. If any issues arise
post-commit it can be easily reverted.

Using this patch I built and ran the LLVM test suite successfully,
which on neoverse-v1 led to the vectorisation of 114 additional
early exit loops. I then performed a bootstrap build of clang,
which built cleanly with 64 extra early exit loops vectorising.

I also built and ran SPEC2017 successfully with no change in
performance for both neoverse-v1 and neoverse-v2.

Author: david-arm

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -396,7 +396,7 @@ static cl::opt<bool> UseWiderVFIfCallVariantsPresent(
     cl::desc("Try wider VFs if they enable the use of vector variants"));
 
 static cl::opt<bool> EnableEarlyExitVectorization(
-    "enable-early-exit-vectorization", cl::init(false), cl::Hidden,
+    "enable-early-exit-vectorization", cl::init(true), cl::Hidden,
     cl::desc(
         "Enable vectorization of early exit loops with uncountable exits."));
 

llvm/test/Transforms/LoopVectorize/AArch64/simple_early_exit.ll

@@ -1,5 +1,5 @@
 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 4
-; RUN: opt -S < %s -p loop-vectorize -enable-early-exit-vectorization | FileCheck %s --check-prefixes=CHECK
+; RUN: opt -S < %s -p loop-vectorize | FileCheck %s --check-prefixes=CHECK
 
 target triple = "aarch64-unknown-linux-gnu"
 

llvm/test/Transforms/LoopVectorize/multi_early_exit.ll

@@ -1,5 +1,5 @@
 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 4
-; RUN: opt -S < %s -p loop-vectorize -enable-early-exit-vectorization | FileCheck %s
+; RUN: opt -S < %s -p loop-vectorize | FileCheck %s
 
 declare void @init_mem(ptr, i64);
 

llvm/test/Transforms/LoopVectorize/multi_early_exit_live_outs.ll

@@ -1,5 +1,5 @@
 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 4
-; RUN: opt -S < %s -p loop-vectorize -enable-early-exit-vectorization | FileCheck %s
+; RUN: opt -S < %s -p loop-vectorize | FileCheck %s
 
 declare void @init_mem(ptr, i64);
 

llvm/test/Transforms/LoopVectorize/single_early_exit.ll

@@ -1,5 +1,5 @@
 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 4
-; RUN: opt -S < %s -p loop-vectorize -enable-early-exit-vectorization -force-vector-width=4 | FileCheck %s
+; RUN: opt -S < %s -p loop-vectorize -force-vector-width=4 | FileCheck %s
 
 declare void @init_mem(ptr, i64);
 

llvm/test/Transforms/LoopVectorize/single_early_exit_live_outs.ll

@@ -1,5 +1,5 @@
 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 4
-; RUN: opt -S < %s -p loop-vectorize -enable-early-exit-vectorization -force-vector-width=4 | FileCheck %s
+; RUN: opt -S < %s -p loop-vectorize -force-vector-width=4 | FileCheck %s
 
 declare void @init_mem(ptr, i64);
 

llvm/test/Transforms/LoopVectorize/single_early_exit_with_outer_loop.ll

@@ -1,4 +1,4 @@
-; RUN: opt -S < %s -p loop-vectorize,'print<loops>' -disable-output -enable-early-exit-vectorization 2>&1 | FileCheck %s
+; RUN: opt -S < %s -p loop-vectorize,'print<loops>' -disable-output 2>&1 | FileCheck %s
 
 declare void @init_mem(ptr, i64);