[llvm] [SimplifyCFG] Don't limit the number of simultaneous forwards from switch condition (PR #95932)

via llvm-commits llvm-commits at lists.llvm.org
Tue Jun 18 07:13:26 PDT 2024


https://github.com/DianQK created https://github.com/llvm/llvm-project/pull/95932

Fixes #95919.

To me, this limit doesn't make sense.

>From 9bd03b4dcc7dc5beb22e5f82c2c8719305d16a21 Mon Sep 17 00:00:00 2001
From: DianQK <dianqk at dianqk.net>
Date: Tue, 18 Jun 2024 21:28:01 +0800
Subject: [PATCH 1/3] Avoid affecting unrelated test cases

---
 llvm/test/CodeGen/AArch64/arm64-jumptable.ll                  | 2 +-
 .../Transforms/SimplifyCFG/Hexagon/switch-to-lookup-table.ll  | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/llvm/test/CodeGen/AArch64/arm64-jumptable.ll b/llvm/test/CodeGen/AArch64/arm64-jumptable.ll
index 7d9adf92a6a95..40b8f721c0505 100644
--- a/llvm/test/CodeGen/AArch64/arm64-jumptable.ll
+++ b/llvm/test/CodeGen/AArch64/arm64-jumptable.ll
@@ -18,7 +18,7 @@ bb3:
 bb4:
   br label %exit.sink.split
 exit.sink.split:
-  %.sink = phi i32 [ 5, %bb4 ], [ %b, %bb1 ], [ 3, %bb3 ], [ %a, %entry ]
+  %.sink = phi i32 [ 5, %bb4 ], [ %b, %bb1 ], [ 7, %bb3 ], [ %a, %entry ]
   store i32 %.sink, ptr %to
   br label %exit
 exit:
diff --git a/llvm/test/Transforms/SimplifyCFG/Hexagon/switch-to-lookup-table.ll b/llvm/test/Transforms/SimplifyCFG/Hexagon/switch-to-lookup-table.ll
index 47dd24e194c39..b3b6abe314e6f 100644
--- a/llvm/test/Transforms/SimplifyCFG/Hexagon/switch-to-lookup-table.ll
+++ b/llvm/test/Transforms/SimplifyCFG/Hexagon/switch-to-lookup-table.ll
@@ -43,7 +43,7 @@ define i32 @foo(i32 %x) #0 section ".tcm_text" {
 ; DISABLE:       sw.default:
 ; DISABLE-NEXT:    br label [[RETURN]]
 ; DISABLE:       return:
-; DISABLE-NEXT:    [[RETVAL_0:%.*]] = phi i32 [ 19, [[SW_DEFAULT]] ], [ 5, [[SW_BB5]] ], [ 12, [[SW_BB4]] ], [ 22, [[SW_BB3]] ], [ 14, [[SW_BB2]] ], [ 20, [[SW_BB1]] ], [ 9, [[ENTRY:%.*]] ]
+; DISABLE-NEXT:    [[RETVAL_0:%.*]] = phi i32 [ 19, [[SW_DEFAULT]] ], [ 33, [[SW_BB5]] ], [ 12, [[SW_BB4]] ], [ 22, [[SW_BB3]] ], [ 14, [[SW_BB2]] ], [ 20, [[SW_BB1]] ], [ 9, [[ENTRY:%.*]] ]
 ; DISABLE-NEXT:    ret i32 [[RETVAL_0]]
 ;
 entry:
@@ -81,7 +81,7 @@ sw.bb4:                                           ; preds = %entry
   br label %return
 
 sw.bb5:                                           ; preds = %entry
-  store i32 5, ptr %retval, align 4
+  store i32 33, ptr %retval, align 4
   br label %return
 
 sw.default:                                       ; preds = %entry

>From 5ddd19a9ff7783c533162e3d99a44c895f3e1241 Mon Sep 17 00:00:00 2001
From: DianQK <dianqk at dianqk.net>
Date: Tue, 18 Jun 2024 21:51:03 +0800
Subject: [PATCH 2/3] Pre-commit test cases

---
 .../ForwardSwitchConditionToPHI.ll            | 69 +++++++++++++++++++
 1 file changed, 69 insertions(+)

diff --git a/llvm/test/Transforms/SimplifyCFG/ForwardSwitchConditionToPHI.ll b/llvm/test/Transforms/SimplifyCFG/ForwardSwitchConditionToPHI.ll
index 5c266f4867398..328c6b93eeec1 100644
--- a/llvm/test/Transforms/SimplifyCFG/ForwardSwitchConditionToPHI.ll
+++ b/llvm/test/Transforms/SimplifyCFG/ForwardSwitchConditionToPHI.ll
@@ -59,6 +59,75 @@ return:                                           ; preds = %entry, %sw.bb4, %sw
   ret i32 %retval.0
 }
 
+define i32 @forward_one(i32 %m) {
+; NO_FWD-LABEL: @forward_one(
+; NO_FWD-NEXT:  entry:
+; NO_FWD-NEXT:    switch i32 [[M:%.*]], label [[SW_BB4:%.*]] [
+; NO_FWD-NEXT:      i32 0, label [[RETURN:%.*]]
+; NO_FWD-NEXT:      i32 1, label [[SW_BB1:%.*]]
+; NO_FWD-NEXT:      i32 2, label [[SW_BB2:%.*]]
+; NO_FWD-NEXT:      i32 3, label [[SW_BB3:%.*]]
+; NO_FWD-NEXT:    ]
+; NO_FWD:       sw.bb1:
+; NO_FWD-NEXT:    br label [[RETURN]]
+; NO_FWD:       sw.bb2:
+; NO_FWD-NEXT:    br label [[RETURN]]
+; NO_FWD:       sw.bb3:
+; NO_FWD-NEXT:    br label [[RETURN]]
+; NO_FWD:       sw.bb4:
+; NO_FWD-NEXT:    br label [[RETURN]]
+; NO_FWD:       return:
+; NO_FWD-NEXT:    [[RETVAL_0:%.*]] = phi i32 [ 4, [[SW_BB4]] ], [ 5, [[SW_BB3]] ], [ 6, [[SW_BB2]] ], [ 1, [[SW_BB1]] ], [ 8, [[ENTRY:%.*]] ]
+; NO_FWD-NEXT:    ret i32 [[RETVAL_0]]
+;
+; FWD-LABEL: @forward_one(
+; FWD-NEXT:  entry:
+; FWD-NEXT:    switch i32 [[M:%.*]], label [[SW_BB4:%.*]] [
+; FWD-NEXT:      i32 0, label [[RETURN:%.*]]
+; FWD-NEXT:      i32 1, label [[SW_BB1:%.*]]
+; FWD-NEXT:      i32 2, label [[SW_BB2:%.*]]
+; FWD-NEXT:      i32 3, label [[SW_BB3:%.*]]
+; FWD-NEXT:    ]
+; FWD:       sw.bb1:
+; FWD-NEXT:    br label [[RETURN]]
+; FWD:       sw.bb2:
+; FWD-NEXT:    br label [[RETURN]]
+; FWD:       sw.bb3:
+; FWD-NEXT:    br label [[RETURN]]
+; FWD:       sw.bb4:
+; FWD-NEXT:    br label [[RETURN]]
+; FWD:       return:
+; FWD-NEXT:    [[RETVAL_0:%.*]] = phi i32 [ 4, [[SW_BB4]] ], [ 5, [[SW_BB3]] ], [ 6, [[SW_BB2]] ], [ 1, [[SW_BB1]] ], [ 8, [[ENTRY:%.*]] ]
+; FWD-NEXT:    ret i32 [[RETVAL_0]]
+;
+entry:
+  switch i32 %m, label %sw.bb4 [
+  i32 0, label %sw.bb0
+  i32 1, label %sw.bb1
+  i32 2, label %sw.bb2
+  i32 3, label %sw.bb3
+  ]
+
+sw.bb0:                                           ; preds = %entry
+  br label %return
+
+sw.bb1:                                           ; preds = %entry
+  br label %return
+
+sw.bb2:                                           ; preds = %entry
+  br label %return
+
+sw.bb3:                                           ; preds = %entry
+  br label %return
+
+sw.bb4:                                           ; preds = %entry
+  br label %return
+
+return:                                           ; preds = %entry, %sw.bb4, %sw.bb3, %sw.bb2, %sw.bb1
+  %retval.0 = phi i32 [ 4, %sw.bb4 ], [ 5, %sw.bb3 ], [ 6, %sw.bb2 ], [ 1, %sw.bb1 ], [ 8, %sw.bb0 ]
+  ret i32 %retval.0
+}
+
 ; If 1 incoming phi value is a case constant of a switch, convert it to the switch condition:
 ; https://bugs.llvm.org/show_bug.cgi?id=34471
 ; This then subsequently should allow squashing of the other trivial case blocks.

>From 26955f37292fde3864715be0b9e64d77dd8008e2 Mon Sep 17 00:00:00 2001
From: DianQK <dianqk at dianqk.net>
Date: Tue, 18 Jun 2024 22:07:12 +0800
Subject: [PATCH 3/3] [SimplifyCFG] Don't limit the number of simultaneous
 forwards from switch condition

---
 llvm/lib/Transforms/Utils/SimplifyCFG.cpp                       | 2 --
 llvm/test/Transforms/SimplifyCFG/ForwardSwitchConditionToPHI.ll | 2 +-
 2 files changed, 1 insertion(+), 3 deletions(-)

diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index 4e2dc7f2b2f4e..5a4c258937a27 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -5818,8 +5818,6 @@ static bool ForwardSwitchConditionToPHI(SwitchInst *SI) {
   for (auto &ForwardingNode : ForwardingNodes) {
     PHINode *Phi = ForwardingNode.first;
     SmallVectorImpl<int> &Indexes = ForwardingNode.second;
-    if (Indexes.size() < 2)
-      continue;
 
     for (int Index : Indexes)
       Phi->setIncomingValue(Index, SI->getCondition());
diff --git a/llvm/test/Transforms/SimplifyCFG/ForwardSwitchConditionToPHI.ll b/llvm/test/Transforms/SimplifyCFG/ForwardSwitchConditionToPHI.ll
index 328c6b93eeec1..5e00a4b098f68 100644
--- a/llvm/test/Transforms/SimplifyCFG/ForwardSwitchConditionToPHI.ll
+++ b/llvm/test/Transforms/SimplifyCFG/ForwardSwitchConditionToPHI.ll
@@ -97,7 +97,7 @@ define i32 @forward_one(i32 %m) {
 ; FWD:       sw.bb4:
 ; FWD-NEXT:    br label [[RETURN]]
 ; FWD:       return:
-; FWD-NEXT:    [[RETVAL_0:%.*]] = phi i32 [ 4, [[SW_BB4]] ], [ 5, [[SW_BB3]] ], [ 6, [[SW_BB2]] ], [ 1, [[SW_BB1]] ], [ 8, [[ENTRY:%.*]] ]
+; FWD-NEXT:    [[RETVAL_0:%.*]] = phi i32 [ 4, [[SW_BB4]] ], [ 5, [[SW_BB3]] ], [ 6, [[SW_BB2]] ], [ [[M]], [[SW_BB1]] ], [ 8, [[ENTRY:%.*]] ]
 ; FWD-NEXT:    ret i32 [[RETVAL_0]]
 ;
 entry:



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