[llvm] [UnifyLoopExits] Never generate phis of only `undef` values (PR #99924)
Johannes Doerfert via llvm-commits
llvm-commits at lists.llvm.org
Mon Jul 22 12:35:22 PDT 2024
https://github.com/jdoerfert updated https://github.com/llvm/llvm-project/pull/99924
>From f2a3e2b6c52d1d83136e9e27992f5a49efc67f72 Mon Sep 17 00:00:00 2001
From: Johannes Doerfert <johannes at jdoerfert.de>
Date: Mon, 22 Jul 2024 11:42:36 -0700
Subject: [PATCH 1/2] [UnifyLoopExits] Precommit test with phis selecting only
`undef`
---
.../Transforms/UnifyLoopExits/undef-phis.ll | 59 +++++++++++++++++++
1 file changed, 59 insertions(+)
create mode 100644 llvm/test/Transforms/UnifyLoopExits/undef-phis.ll
diff --git a/llvm/test/Transforms/UnifyLoopExits/undef-phis.ll b/llvm/test/Transforms/UnifyLoopExits/undef-phis.ll
new file mode 100644
index 0000000000000..1c71ddc0f7abb
--- /dev/null
+++ b/llvm/test/Transforms/UnifyLoopExits/undef-phis.ll
@@ -0,0 +1,59 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt < %s -passes='unify-loop-exits' -S | FileCheck %s
+
+define fastcc void @undef_phi(i64 %i5247, i1 %i4530, i1 %i4936.not) {
+; CHECK-LABEL: define fastcc void @undef_phi(
+; CHECK-SAME: i64 [[I5247:%.*]], i1 [[I4530:%.*]], i1 [[I4936_NOT:%.*]]) {
+; CHECK-NEXT: [[BB:.*:]]
+; CHECK-NEXT: br label %[[MBB3932:.*]]
+; CHECK: [[MBB3932]]:
+; CHECK-NEXT: br label %[[MBB4454:.*]]
+; CHECK: [[MBB4321:.*]]:
+; CHECK-NEXT: [[TMP0:%.*]] = trunc i64 [[I5247]] to i32
+; CHECK-NEXT: [[I5290:%.*]] = icmp eq i32 [[TMP0]], 0
+; CHECK-NEXT: br i1 [[I5290]], label %[[MBB3932]], label %[[LOOP_EXIT_GUARD:.*]]
+; CHECK: [[MBB4454]]:
+; CHECK-NEXT: br i1 [[I4530]], label %[[MBB4535:.*]], label %[[LOOP_EXIT_GUARD1:.*]]
+; CHECK: [[MBB4531:.*]]:
+; CHECK-NEXT: ret void
+; CHECK: [[MBB4535]]:
+; CHECK-NEXT: br i1 [[I4936_NOT]], label %[[LOOP_EXIT_GUARD1]], label %[[MBB4454]]
+; CHECK: [[MBB5291:.*]]:
+; CHECK-NEXT: [[I5293:%.*]] = insertvalue [2 x i32] zeroinitializer, i32 [[DOTMOVED:%.*]], 1
+; CHECK-NEXT: store volatile [2 x i32] [[I5293]], ptr addrspace(5) null, align 4
+; CHECK-NEXT: ret void
+; CHECK: [[LOOP_EXIT_GUARD]]:
+; CHECK-NEXT: [[DOTMOVED]] = phi i32 [ [[TMP0]], %[[MBB4321]] ], [ [[DOTMOVED_MOVED:%.*]], %[[LOOP_EXIT_GUARD1]] ]
+; CHECK-NEXT: [[GUARD_MBB4531:%.*]] = phi i1 [ false, %[[MBB4321]] ], [ [[GUARD_MBB4531_MOVED:%.*]], %[[LOOP_EXIT_GUARD1]] ]
+; CHECK-NEXT: br i1 [[GUARD_MBB4531]], label %[[MBB4531]], label %[[MBB5291]]
+; CHECK: [[LOOP_EXIT_GUARD1]]:
+; CHECK-NEXT: [[GUARD_MBB4531_MOVED]] = phi i1 [ true, %[[MBB4454]] ], [ undef, %[[MBB4535]] ]
+; CHECK-NEXT: [[DOTMOVED_MOVED]] = phi i32 [ poison, %[[MBB4454]] ], [ undef, %[[MBB4535]] ]
+; CHECK-NEXT: [[GUARD_LOOP_EXIT_GUARD:%.*]] = phi i1 [ true, %[[MBB4454]] ], [ false, %[[MBB4535]] ]
+; CHECK-NEXT: br i1 [[GUARD_LOOP_EXIT_GUARD]], label %[[LOOP_EXIT_GUARD]], label %[[MBB4321]]
+;
+mbb:
+ br label %mbb3932
+
+mbb3932: ; preds = %mbb4321, %mbb
+ br label %mbb4454
+
+mbb4321: ; preds = %mbb4535
+ %0 = trunc i64 %i5247 to i32
+ %i5290 = icmp eq i32 %0, 0
+ br i1 %i5290, label %mbb3932, label %mbb5291
+
+mbb4454: ; preds = %mbb4535, %mbb3932
+ br i1 %i4530, label %mbb4535, label %mbb4531
+
+mbb4531: ; preds = %mbb4454
+ ret void
+
+mbb4535: ; preds = %mbb4454
+ br i1 %i4936.not, label %mbb4321, label %mbb4454
+
+mbb5291: ; preds = %mbb4321
+ %i5293 = insertvalue [2 x i32] zeroinitializer, i32 %0, 1
+ store volatile [2 x i32] %i5293, ptr addrspace(5) null, align 4
+ ret void
+}
>From 8e73162881a01e7064a35784e35282c7f512bcde Mon Sep 17 00:00:00 2001
From: Johannes Doerfert <johannes at jdoerfert.de>
Date: Mon, 22 Jul 2024 11:13:32 -0700
Subject: [PATCH 2/2] [BasicBlockUtils] Never emit PHIs that are known to be
`undef`
There are (rare) cases we used to emit a PHI node with only `undef`
inputs, that's not helpful.
---
llvm/lib/Transforms/Utils/BasicBlockUtils.cpp | 11 +++++++++--
llvm/test/Transforms/UnifyLoopExits/undef-phis.ll | 3 +--
2 files changed, 10 insertions(+), 4 deletions(-)
diff --git a/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp b/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
index 462283c0bfe00..4c8cfa5c6c697 100644
--- a/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
+++ b/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
@@ -1909,22 +1909,29 @@ static void reconnectPhis(BasicBlock *Out, BasicBlock *GuardBlock,
auto NewPhi =
PHINode::Create(Phi->getType(), Incoming.size(),
Phi->getName() + ".moved", FirstGuardBlock->begin());
+ bool AllUndef = true;
for (auto *In : Incoming) {
Value *V = UndefValue::get(Phi->getType());
if (In == Out) {
V = NewPhi;
} else if (Phi->getBasicBlockIndex(In) != -1) {
V = Phi->removeIncomingValue(In, false);
+ AllUndef &= isa<UndefValue>(V);
}
NewPhi->addIncoming(V, In);
}
assert(NewPhi->getNumIncomingValues() == Incoming.size());
+ Value *NewV = NewPhi;
+ if (AllUndef) {
+ NewPhi->eraseFromParent();
+ NewV = UndefValue::get(Phi->getType());
+ }
if (Phi->getNumOperands() == 0) {
- Phi->replaceAllUsesWith(NewPhi);
+ Phi->replaceAllUsesWith(NewV);
I = Phi->eraseFromParent();
continue;
}
- Phi->addIncoming(NewPhi, GuardBlock);
+ Phi->addIncoming(NewV, GuardBlock);
++I;
}
}
diff --git a/llvm/test/Transforms/UnifyLoopExits/undef-phis.ll b/llvm/test/Transforms/UnifyLoopExits/undef-phis.ll
index 1c71ddc0f7abb..722ccc519a764 100644
--- a/llvm/test/Transforms/UnifyLoopExits/undef-phis.ll
+++ b/llvm/test/Transforms/UnifyLoopExits/undef-phis.ll
@@ -23,12 +23,11 @@ define fastcc void @undef_phi(i64 %i5247, i1 %i4530, i1 %i4936.not) {
; CHECK-NEXT: store volatile [2 x i32] [[I5293]], ptr addrspace(5) null, align 4
; CHECK-NEXT: ret void
; CHECK: [[LOOP_EXIT_GUARD]]:
-; CHECK-NEXT: [[DOTMOVED]] = phi i32 [ [[TMP0]], %[[MBB4321]] ], [ [[DOTMOVED_MOVED:%.*]], %[[LOOP_EXIT_GUARD1]] ]
+; CHECK-NEXT: [[DOTMOVED]] = phi i32 [ [[TMP0]], %[[MBB4321]] ], [ undef, %[[LOOP_EXIT_GUARD1]] ]
; CHECK-NEXT: [[GUARD_MBB4531:%.*]] = phi i1 [ false, %[[MBB4321]] ], [ [[GUARD_MBB4531_MOVED:%.*]], %[[LOOP_EXIT_GUARD1]] ]
; CHECK-NEXT: br i1 [[GUARD_MBB4531]], label %[[MBB4531]], label %[[MBB5291]]
; CHECK: [[LOOP_EXIT_GUARD1]]:
; CHECK-NEXT: [[GUARD_MBB4531_MOVED]] = phi i1 [ true, %[[MBB4454]] ], [ undef, %[[MBB4535]] ]
-; CHECK-NEXT: [[DOTMOVED_MOVED]] = phi i32 [ poison, %[[MBB4454]] ], [ undef, %[[MBB4535]] ]
; CHECK-NEXT: [[GUARD_LOOP_EXIT_GUARD:%.*]] = phi i1 [ true, %[[MBB4454]] ], [ false, %[[MBB4535]] ]
; CHECK-NEXT: br i1 [[GUARD_LOOP_EXIT_GUARD]], label %[[LOOP_EXIT_GUARD]], label %[[MBB4321]]
;
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