[llvm] [JumpThreading] Thread over BB with only an unconditional branch (PR #86312)
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Fri Mar 22 10:16:04 PDT 2024
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-llvm-transforms
Author: XChy (XChy)
<details>
<summary>Changes</summary>
Fixes #<!-- -->76609
This patch does:
- relax the phis constraint in `CanRedirectPredsOfEmptyBBToSucc`
- guarantee the BB whose preds are redirected has multiple different predecessors, so that it can handle the case without phis in BB. Without this change and phi constraint, we may redirect the CommonPred.
---
Full diff: https://github.com/llvm/llvm-project/pull/86312.diff
5 Files Affected:
- (modified) llvm/lib/Transforms/Utils/Local.cpp (+5-4)
- (modified) llvm/test/Transforms/JumpThreading/pr79175.ll (+4-4)
- (modified) llvm/test/Transforms/JumpThreading/select.ll (+28-26)
- (modified) llvm/test/Transforms/JumpThreading/thread-prob-7.ll (+4-4)
- (added) llvm/test/Transforms/JumpThreading/uncond-no-phi.ll (+123)
``````````diff
diff --git a/llvm/lib/Transforms/Utils/Local.cpp b/llvm/lib/Transforms/Utils/Local.cpp
index 422319eb185134..9760988e5c09d7 100644
--- a/llvm/lib/Transforms/Utils/Local.cpp
+++ b/llvm/lib/Transforms/Utils/Local.cpp
@@ -1013,12 +1013,13 @@ CanRedirectPredsOfEmptyBBToSucc(BasicBlock *BB, BasicBlock *Succ,
const SmallPtrSetImpl<BasicBlock *> &SuccPreds,
BasicBlock *&CommonPred) {
- // There must be phis in BB, otherwise BB will be merged into Succ directly
- if (BB->phis().empty() || Succ->phis().empty())
+ // Only handle the nontrivial case. Assume we need to update the phi of succ
+ // here.
+ if (Succ->phis().empty())
return false;
- // BB must have predecessors not shared that can be redirected to Succ
- if (!BB->hasNPredecessorsOrMore(2))
+ // BB must have multiple different uncommon predecessors that can be redirected to Succ
+ if (BB->getUniquePredecessor() || pred_empty(BB))
return false;
// Get single common predecessors of both BB and Succ
diff --git a/llvm/test/Transforms/JumpThreading/pr79175.ll b/llvm/test/Transforms/JumpThreading/pr79175.ll
index 2c7ee0770cdc73..cce30ce079999c 100644
--- a/llvm/test/Transforms/JumpThreading/pr79175.ll
+++ b/llvm/test/Transforms/JumpThreading/pr79175.ll
@@ -17,11 +17,11 @@ define i32 @test(i64 %idx, i32 %val) {
; CHECK: cond.end:
; CHECK-NEXT: [[CMP_I:%.*]] = icmp sgt i32 [[VAL]], 0
; CHECK-NEXT: [[COND_FR:%.*]] = freeze i1 [[CMP_I]]
-; CHECK-NEXT: br i1 [[COND_FR]], label [[COND_END_THREAD]], label [[TMP0:%.*]]
-; CHECK: cond.end.thread:
-; CHECK-NEXT: br label [[TMP0]]
+; CHECK-NEXT: br i1 [[COND_FR]], label [[TMP0:%.*]], label [[COND_END_THREAD]]
; CHECK: 0:
-; CHECK-NEXT: [[TMP1:%.*]] = phi i32 [ 0, [[COND_END_THREAD]] ], [ [[VAL]], [[COND_END]] ]
+; CHECK-NEXT: br label [[COND_END_THREAD]]
+; CHECK: cond.end.thread:
+; CHECK-NEXT: [[TMP1:%.*]] = phi i32 [ [[VAL]], [[COND_END]] ], [ 0, [[TMP0]] ], [ 0, [[FOR_BODY]] ]
; CHECK-NEXT: [[F_IDX:%.*]] = getelementptr inbounds i32, ptr @f, i64 [[IDX]]
; CHECK-NEXT: store i32 [[TMP1]], ptr [[F_IDX]], align 4
; CHECK-NEXT: [[F_RELOAD:%.*]] = load i32, ptr @f, align 4
diff --git a/llvm/test/Transforms/JumpThreading/select.ll b/llvm/test/Transforms/JumpThreading/select.ll
index 4ec55a66bb8ac1..53aebeb7b05c0d 100644
--- a/llvm/test/Transforms/JumpThreading/select.ll
+++ b/llvm/test/Transforms/JumpThreading/select.ll
@@ -21,7 +21,7 @@ declare void @quux()
; booleans where at least one operand is true/false/undef.
;.
-; CHECK: @[[ANCHOR:[a-zA-Z0-9_$"\\.-]+]] = constant [3 x ptr] [ptr blockaddress(@test_indirectbr, [[L1:%.*]]), ptr inttoptr (i32 1 to ptr), ptr blockaddress(@test_indirectbr, [[L3:%.*]])]
+; CHECK-BPI: @anchor = constant [3 x ptr] [ptr blockaddress(@test_indirectbr, %L1), ptr inttoptr (i32 1 to ptr), ptr blockaddress(@test_indirectbr, %L3)]
;.
define void @test_br(i1 %cond, i1 %value) nounwind {
; CHECK-LABEL: @test_br(
@@ -66,8 +66,8 @@ define void @test_switch(i1 %cond, i8 %value) nounwind {
; CHECK-NEXT: call void @quux()
; CHECK-NEXT: [[EXPR:%.*]] = select i1 [[COND]], i8 1, i8 [[VALUE:%.*]]
; CHECK-NEXT: switch i8 [[EXPR]], label [[L3:%.*]] [
-; CHECK-NEXT: i8 1, label [[L1]]
-; CHECK-NEXT: i8 2, label [[L2:%.*]]
+; CHECK-NEXT: i8 1, label [[L1]]
+; CHECK-NEXT: i8 2, label [[L2:%.*]]
; CHECK-NEXT: ]
; CHECK: L1:
; CHECK-NEXT: call void @foo()
@@ -192,8 +192,8 @@ define void @test_switch_cmp(i1 %cond, i32 %val, i8 %value) nounwind {
; CHECK: 0:
; CHECK-NEXT: [[TMP1:%.*]] = phi i8 [ [[VALUE:%.*]], [[L0]] ]
; CHECK-NEXT: switch i8 [[TMP1]], label [[L3:%.*]] [
-; CHECK-NEXT: i8 1, label [[L1]]
-; CHECK-NEXT: i8 2, label [[L2:%.*]]
+; CHECK-NEXT: i8 1, label [[L1]]
+; CHECK-NEXT: i8 2, label [[L2:%.*]]
; CHECK-NEXT: ]
; CHECK: L1:
; CHECK-NEXT: call void @foo()
@@ -237,8 +237,8 @@ define void @test_switch_default(ptr nocapture %status) nounwind {
; CHECK-NEXT: entry:
; CHECK-NEXT: [[TMP0:%.*]] = load i32, ptr [[STATUS:%.*]], align 4
; CHECK-NEXT: switch i32 [[TMP0]], label [[L2:%.*]] [
-; CHECK-NEXT: i32 5061, label [[L2_THREAD:%.*]]
-; CHECK-NEXT: i32 0, label [[L2]]
+; CHECK-NEXT: i32 5061, label [[L2_THREAD:%.*]]
+; CHECK-NEXT: i32 0, label [[L2]]
; CHECK-NEXT: ]
; CHECK: L2.thread:
; CHECK-NEXT: store i32 10025, ptr [[STATUS]], align 4
@@ -377,21 +377,21 @@ define i32 @unfold3(i32 %u, i32 %v, i32 %w, i32 %x, i32 %y, i32 %z, i32 %j) noun
; CHECK-NEXT: br i1 [[CMP_I]], label [[DOTEXIT_THREAD4:%.*]], label [[COND_FALSE_I:%.*]]
; CHECK: cond.false.i:
; CHECK-NEXT: [[CMP4_I:%.*]] = icmp sgt i32 [[U]], [[V]]
-; CHECK-NEXT: br i1 [[CMP4_I]], label [[DOTEXIT_THREAD:%.*]], label [[COND_FALSE_6_I:%.*]]
+; CHECK-NEXT: br i1 [[CMP4_I]], label [[DOTEXIT_THREAD4]], label [[COND_FALSE_6_I:%.*]]
; CHECK: cond.false.6.i:
; CHECK-NEXT: [[CMP8_I:%.*]] = icmp slt i32 [[W:%.*]], [[X:%.*]]
; CHECK-NEXT: br i1 [[CMP8_I]], label [[DOTEXIT_THREAD4]], label [[COND_FALSE_10_I:%.*]]
; CHECK: cond.false.10.i:
; CHECK-NEXT: [[CMP13_I:%.*]] = icmp sgt i32 [[W]], [[X]]
-; CHECK-NEXT: br i1 [[CMP13_I]], label [[DOTEXIT_THREAD]], label [[DOTEXIT:%.*]]
+; CHECK-NEXT: br i1 [[CMP13_I]], label [[DOTEXIT_THREAD4]], label [[DOTEXIT:%.*]]
; CHECK: .exit:
; CHECK-NEXT: [[PHITMP:%.*]] = icmp sge i32 [[Y:%.*]], [[Z:%.*]]
; CHECK-NEXT: [[COND_FR:%.*]] = freeze i1 [[PHITMP]]
-; CHECK-NEXT: br i1 [[COND_FR]], label [[DOTEXIT_THREAD]], label [[DOTEXIT_THREAD4]]
-; CHECK: .exit.thread:
+; CHECK-NEXT: br i1 [[COND_FR]], label [[DOTEXIT_THREAD:%.*]], label [[DOTEXIT_THREAD4]]
+; CHECK: 0:
; CHECK-NEXT: br label [[DOTEXIT_THREAD4]]
-; CHECK: .exit.thread4:
-; CHECK-NEXT: [[TMP0:%.*]] = phi i32 [ [[J]], [[DOTEXIT_THREAD]] ], [ [[ADD3]], [[DOTEXIT]] ], [ [[ADD3]], [[ENTRY:%.*]] ], [ [[ADD3]], [[COND_FALSE_6_I]] ]
+; CHECK: .exit.thread:
+; CHECK-NEXT: [[TMP0:%.*]] = phi i32 [ [[ADD3]], [[DOTEXIT]] ], [ [[J]], [[DOTEXIT_THREAD]] ], [ [[J]], [[COND_FALSE_I]] ], [ [[J]], [[COND_FALSE_10_I]] ], [ [[ADD3]], [[ENTRY:%.*]] ], [ [[ADD3]], [[COND_FALSE_6_I]] ]
; CHECK-NEXT: ret i32 [[TMP0]]
;
entry:
@@ -430,23 +430,23 @@ define i32 @unfold4(i32 %u, i32 %v, i32 %w, i32 %x, i32 %y, i32 %z, i32 %j) noun
; CHECK-NEXT: br i1 [[CMP_I]], label [[DOTEXIT_THREAD:%.*]], label [[COND_FALSE_I:%.*]]
; CHECK: cond.false.i:
; CHECK-NEXT: [[CMP4_I:%.*]] = icmp sgt i32 [[U]], [[V]]
-; CHECK-NEXT: br i1 [[CMP4_I]], label [[DOTEXIT_THREAD5:%.*]], label [[COND_FALSE_6_I:%.*]]
+; CHECK-NEXT: br i1 [[CMP4_I]], label [[DOTEXIT_THREAD]], label [[COND_FALSE_6_I:%.*]]
; CHECK: cond.false.6.i:
; CHECK-NEXT: [[CMP8_I:%.*]] = icmp slt i32 [[W:%.*]], [[X:%.*]]
; CHECK-NEXT: br i1 [[CMP8_I]], label [[DOTEXIT_THREAD]], label [[COND_FALSE_10_I:%.*]]
; CHECK: cond.false.10.i:
; CHECK-NEXT: [[CMP13_I:%.*]] = icmp sgt i32 [[W]], [[X]]
-; CHECK-NEXT: br i1 [[CMP13_I]], label [[DOTEXIT_THREAD5]], label [[DOTEXIT:%.*]]
+; CHECK-NEXT: br i1 [[CMP13_I]], label [[DOTEXIT_THREAD]], label [[DOTEXIT:%.*]]
; CHECK: .exit:
; CHECK-NEXT: [[CMP19_I:%.*]] = icmp sge i32 [[Y:%.*]], [[Z:%.*]]
; CHECK-NEXT: [[CONV:%.*]] = zext i1 [[CMP19_I]] to i32
; CHECK-NEXT: [[LNOT_I18:%.*]] = icmp eq i32 [[CONV]], 1
; CHECK-NEXT: [[COND_FR:%.*]] = freeze i1 [[LNOT_I18]]
-; CHECK-NEXT: br i1 [[COND_FR]], label [[DOTEXIT_THREAD]], label [[DOTEXIT_THREAD5]]
+; CHECK-NEXT: br i1 [[COND_FR]], label [[TMP1:%.*]], label [[DOTEXIT_THREAD]]
+; CHECK: 0:
+; CHECK-NEXT: br label [[DOTEXIT_THREAD]]
; CHECK: .exit.thread:
-; CHECK-NEXT: br label [[DOTEXIT_THREAD5]]
-; CHECK: .exit.thread5:
-; CHECK-NEXT: [[TMP0:%.*]] = phi i32 [ [[J]], [[DOTEXIT_THREAD]] ], [ [[ADD3]], [[DOTEXIT]] ], [ [[ADD3]], [[COND_FALSE_I]] ], [ [[ADD3]], [[COND_FALSE_10_I]] ]
+; CHECK-NEXT: [[TMP0:%.*]] = phi i32 [ [[ADD3]], [[DOTEXIT]] ], [ [[J]], [[TMP1]] ], [ [[J]], [[ENTRY:%.*]] ], [ [[J]], [[COND_FALSE_6_I]] ], [ [[ADD3]], [[COND_FALSE_I]] ], [ [[ADD3]], [[COND_FALSE_10_I]] ]
; CHECK-NEXT: ret i32 [[TMP0]]
;
entry:
@@ -560,10 +560,10 @@ define void @test_func(ptr nocapture readonly %a, ptr nocapture readonly %b, ptr
; CHECK: if.end:
; CHECK-NEXT: [[LOCAL_VAR_0:%.*]] = phi i32 [ [[TMP1]], [[FOR_BODY]] ]
; CHECK-NEXT: switch i32 [[LOCAL_VAR_0]], label [[SW_DEFAULT]] [
-; CHECK-NEXT: i32 2, label [[SW_BB]]
-; CHECK-NEXT: i32 4, label [[SW_BB7]]
-; CHECK-NEXT: i32 5, label [[SW_BB8:%.*]]
-; CHECK-NEXT: i32 7, label [[SW_BB9:%.*]]
+; CHECK-NEXT: i32 2, label [[SW_BB]]
+; CHECK-NEXT: i32 4, label [[SW_BB7]]
+; CHECK-NEXT: i32 5, label [[SW_BB8:%.*]]
+; CHECK-NEXT: i32 7, label [[SW_BB9:%.*]]
; CHECK-NEXT: ]
; CHECK: sw.bb:
; CHECK-NEXT: call void @foo()
@@ -669,8 +669,10 @@ if.end:
!0 = !{!"branch_weights", i64 1073741824, i64 3221225472}
!1 = !{!"function_entry_count", i64 1984}
;.
-; CHECK: attributes #[[ATTR0:[0-9]+]] = { nounwind }
+; CHECK-BPI: attributes #[[ATTR0:[0-9]+]] = { nounwind }
;.
-; CHECK: [[META0:![0-9]+]] = !{!"function_entry_count", i64 1984}
-; CHECK: [[PROF1]] = !{!"branch_weights", i64 1073741824, i64 3221225472}
+; CHECK-BPI: [[META0:![0-9]+]] = !{!"function_entry_count", i64 1984}
+; CHECK-BPI: [[PROF1]] = !{!"branch_weights", i64 1073741824, i64 3221225472}
;.
+;; NOTE: These prefixes are unused and the list is autogenerated. Do not add tests below this line:
+; CHECK-BPI: {{.*}}
diff --git a/llvm/test/Transforms/JumpThreading/thread-prob-7.ll b/llvm/test/Transforms/JumpThreading/thread-prob-7.ll
index 8c9d89871d00b3..4623a579be48f6 100644
--- a/llvm/test/Transforms/JumpThreading/thread-prob-7.ll
+++ b/llvm/test/Transforms/JumpThreading/thread-prob-7.ll
@@ -14,15 +14,15 @@ define i32 @func0(i32 %a0, i32 %a1) !prof !0 {
; CHECK-NEXT: br i1 [[CMP1]], label [[BB_JOIN_THREAD:%.*]], label [[TEST2_FALSE:%.*]], !prof [[PROF2:![0-9]+]]
; CHECK: test2_false:
; CHECK-NEXT: call void @foobar()
-; CHECK-NEXT: br label [[TMP0:%.*]]
+; CHECK-NEXT: br label [[BB_JOIN_THREAD]]
; CHECK: bb_join:
; CHECK-NEXT: [[C:%.*]] = phi i1 [ [[CX]], [[ENTRY:%.*]] ]
; CHECK-NEXT: [[COND_FR:%.*]] = freeze i1 [[C]]
-; CHECK-NEXT: br i1 [[COND_FR]], label [[BB_JOIN_THREAD]], label [[TMP0]], !prof [[PROF3:![0-9]+]]
+; CHECK-NEXT: br i1 [[COND_FR]], label [[BB_JOIN_THREAD1:%.*]], label [[BB_JOIN_THREAD]], !prof [[PROF3:![0-9]+]]
; CHECK: bb_join.thread:
-; CHECK-NEXT: br label [[TMP0]]
+; CHECK-NEXT: br label [[BB_JOIN_THREAD]]
; CHECK: 0:
-; CHECK-NEXT: [[TMP1:%.*]] = phi i32 [ 42, [[BB_JOIN_THREAD]] ], [ 7, [[BB_JOIN]] ], [ 7, [[TEST2_FALSE]] ]
+; CHECK-NEXT: [[TMP1:%.*]] = phi i32 [ 7, [[BB_JOIN]] ], [ 7, [[TEST2_FALSE]] ], [ 42, [[TEST2]] ], [ 42, [[BB_JOIN_THREAD1]] ]
; CHECK-NEXT: ret i32 [[TMP1]]
;
entry:
diff --git a/llvm/test/Transforms/JumpThreading/uncond-no-phi.ll b/llvm/test/Transforms/JumpThreading/uncond-no-phi.ll
new file mode 100644
index 00000000000000..6104e8f8778bc0
--- /dev/null
+++ b/llvm/test/Transforms/JumpThreading/uncond-no-phi.ll
@@ -0,0 +1,123 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 4
+; RUN: opt -passes=jump-threading -S < %s | FileCheck %s
+
+define i1 @if_else(i1 %c, i1 %c1) {
+; CHECK-LABEL: define i1 @if_else(
+; CHECK-SAME: i1 [[C:%.*]], i1 [[C1:%.*]]) {
+; CHECK-NEXT: entry:
+; CHECK-NEXT: br i1 [[C]], label [[THEN:%.*]], label [[RETURN:%.*]]
+; CHECK: then:
+; CHECK-NEXT: call void @dummy()
+; CHECK-NEXT: br i1 [[C1]], label [[ELSE:%.*]], label [[RETURN]]
+; CHECK: else:
+; CHECK-NEXT: br label [[RETURN]]
+; CHECK: return:
+; CHECK-NEXT: [[RETVAL_0:%.*]] = phi i1 [ false, [[THEN]] ], [ true, [[ENTRY:%.*]] ], [ true, [[ELSE]] ]
+; CHECK-NEXT: ret i1 [[RETVAL_0]]
+;
+entry:
+ br i1 %c, label %then, label %else
+
+then:
+ call void @dummy()
+ br i1 %c1, label %else, label %return
+
+else:
+ br label %return
+
+return:
+ %retval.0 = phi i1 [ true, %else ], [ false, %then ]
+ ret i1 %retval.0
+}
+
+define i8 @switch_uncond(i8 %arg) {
+; CHECK-LABEL: define i8 @switch_uncond(
+; CHECK-SAME: i8 [[ARG:%.*]]) {
+; CHECK-NEXT: entry:
+; CHECK-NEXT: switch i8 [[ARG]], label [[DEFAULT:%.*]] [
+; CHECK-NEXT: i8 0, label [[BB1:%.*]]
+; CHECK-NEXT: i8 1, label [[BB3:%.*]]
+; CHECK-NEXT: i8 2, label [[BB2:%.*]]
+; CHECK-NEXT: i8 3, label [[END:%.*]]
+; CHECK-NEXT: ]
+; CHECK: default:
+; CHECK-NEXT: unreachable
+; CHECK: bb:
+; CHECK-NEXT: call void @dummy()
+; CHECK-NEXT: br label [[END]]
+; CHECK: bb1:
+; CHECK-NEXT: call void @dummy()
+; CHECK-NEXT: br label [[END]]
+; CHECK: bb2:
+; CHECK-NEXT: br label [[END]]
+; CHECK: end:
+; CHECK-NEXT: [[PHI:%.*]] = phi i8 [ 1, [[ENTRY:%.*]] ], [ 0, [[BB3]] ], [ 0, [[BB1]] ], [ 0, [[BB2]] ]
+; CHECK-NEXT: ret i8 [[PHI]]
+;
+entry:
+ switch i8 %arg, label %default [
+ i8 0, label %bb
+ i8 1, label %bb1
+ i8 2, label %bb2
+ i8 3, label %end
+ ]
+
+default:
+ unreachable
+
+bb:
+ call void @dummy()
+ br label %bb2
+
+bb1:
+ call void @dummy()
+ br label %bb2
+
+; Predecessors of %bb2 are %bb and %bb1, they are not identical.
+; So we can thread %bb2.
+bb2:
+ br label %end
+
+end:
+ %phi = phi i8 [ 0, %bb2 ], [ 1, %entry ]
+ ret i8 %phi
+}
+
+define i8 @switch_uncond_fail(i8 %arg) {
+; CHECK-LABEL: define i8 @switch_uncond_fail(
+; CHECK-SAME: i8 [[ARG:%.*]]) {
+; CHECK-NEXT: entry:
+; CHECK-NEXT: switch i8 [[ARG]], label [[DEFAULT:%.*]] [
+; CHECK-NEXT: i8 0, label [[BB:%.*]]
+; CHECK-NEXT: i8 1, label [[BB]]
+; CHECK-NEXT: i8 2, label [[END:%.*]]
+; CHECK-NEXT: ]
+; CHECK: default:
+; CHECK-NEXT: br label [[END]]
+; CHECK: bb:
+; CHECK-NEXT: br label [[END]]
+; CHECK: end:
+; CHECK-NEXT: [[PHI:%.*]] = phi i8 [ 0, [[BB]] ], [ 1, [[ENTRY:%.*]] ], [ 2, [[DEFAULT]] ]
+; CHECK-NEXT: ret i8 [[PHI]]
+;
+entry:
+ switch i8 %arg, label %default [
+ i8 0, label %bb
+ i8 1, label %bb
+ i8 2, label %end
+ ]
+
+default:
+ br label %end
+
+; Predecessor of %bb is only %entry (though there are two in predecessor list),
+; thus it's unthreadable.
+bb:
+ br label %end
+
+end:
+ %phi = phi i8 [ 0, %bb ], [ 1, %entry ], [ 2, %default ]
+ ret i8 %phi
+}
+
+declare void @dummy()
``````````
</details>
https://github.com/llvm/llvm-project/pull/86312
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