[llvm] [LoopRotate] Don't rotate loops when the minsize attribute is present (PR #98815)
via llvm-commits
llvm-commits at lists.llvm.org
Sun Jul 14 07:04:23 PDT 2024
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-llvm-transforms
Author: Ayke (aykevl)
<details>
<summary>Changes</summary>
The main use for this patch is LTO. It is not (yet?) possible to set the size level (-Os, -Oz) in the linker, which means loops are still rotated even if -Oz is specified on the command line. Therefore, look at the function attribute instead of only at the size level to determine whether to rotate loops for a given function.
For discussion, see: https://reviews.llvm.org/D119342
An older version of this patch was already approved at https://reviews.llvm.org/D119342 but I never got around to committing it. The code changed so I had to make some minor updates to this patch and in the meantime I also lost commit access because I wasn't really using it. So here is an updated patch.
---
Full diff: https://github.com/llvm/llvm-project/pull/98815.diff
2 Files Affected:
- (modified) llvm/lib/Transforms/Scalar/LoopRotation.cpp (+5-4)
- (added) llvm/test/Transforms/LoopRotate/minsize-disable.ll (+32)
``````````diff
diff --git a/llvm/lib/Transforms/Scalar/LoopRotation.cpp b/llvm/lib/Transforms/Scalar/LoopRotation.cpp
index 072859af4c5f9..acb79e94d087c 100644
--- a/llvm/lib/Transforms/Scalar/LoopRotation.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopRotation.cpp
@@ -64,10 +64,11 @@ PreservedAnalyses LoopRotatePass::run(Loop &L, LoopAnalysisManager &AM,
// Vectorization requires loop-rotation. Use default threshold for loops the
// user explicitly marked for vectorization, even when header duplication is
// disabled.
- int Threshold = EnableHeaderDuplication ||
- hasVectorizeTransformation(&L) == TM_ForcedByUser
- ? DefaultRotationThreshold
- : 0;
+ int Threshold =
+ (EnableHeaderDuplication && !L.getHeader()->getParent()->hasMinSize()) ||
+ hasVectorizeTransformation(&L) == TM_ForcedByUser
+ ? DefaultRotationThreshold
+ : 0;
const DataLayout &DL = L.getHeader()->getDataLayout();
const SimplifyQuery SQ = getBestSimplifyQuery(AR, DL);
diff --git a/llvm/test/Transforms/LoopRotate/minsize-disable.ll b/llvm/test/Transforms/LoopRotate/minsize-disable.ll
new file mode 100644
index 0000000000000..2db87b3ce8291
--- /dev/null
+++ b/llvm/test/Transforms/LoopRotate/minsize-disable.ll
@@ -0,0 +1,32 @@
+; REQUIRES: asserts
+; RUN: opt < %s -S -passes=loop-rotate -debug -debug-only=loop-rotate 2>&1 | FileCheck %s
+
+; Loop should not be rotated for functions with the minsize attribute.
+; This is mostly useful for LTO which doesn't (yet) understand -Oz.
+; CHECK: LoopRotation: NOT rotating - contains 2 instructions, which is more
+
+ at e = global i32 10
+
+declare void @use(i32)
+
+; Function attrs: minsize optsize
+define void @test() #0 {
+entry:
+ %end = load i32, ptr @e
+ br label %loop
+
+loop:
+ %n.phi = phi i32 [ %n, %loop.fin ], [ 0, %entry ]
+ %cond = icmp eq i32 %n.phi, %end
+ br i1 %cond, label %exit, label %loop.fin
+
+loop.fin:
+ %n = add i32 %n.phi, 1
+ call void @use(i32 %n)
+ br label %loop
+
+exit:
+ ret void
+}
+
+attributes #0 = { minsize optsize }
``````````
</details>
https://github.com/llvm/llvm-project/pull/98815
More information about the llvm-commits
mailing list