[llvm] [SimplifyCFG] Handle trunc condition in foldBranchToCommonDest. (PR #135490)

[Andreas Jonson via llvm-commits]

https://github.com/andjo403 updated https://github.com/llvm/llvm-project/pull/135490

>From ca29cef6d0d4110290226d3a09f5ed14df8c7677 Mon Sep 17 00:00:00 2001
From: Andreas Jonson <andjo403 at hotmail.com>
Date: Sat, 12 Apr 2025 12:36:52 +0200
Subject: [PATCH] [SimplifyCFG] Handle trunc condition in
 foldBranchToCommonDest.

---
 llvm/lib/Transforms/Utils/SimplifyCFG.cpp             |  4 +---
 .../SimplifyCFG/X86/switch_to_lookup_table.ll         | 11 +++++------
 .../SimplifyCFG/X86/switch_to_lookup_table_big.ll     |  7 +++----
 .../SimplifyCFG/fold-branch-to-common-dest.ll         |  5 ++---
 4 files changed, 11 insertions(+), 16 deletions(-)

diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index eac7e7c209c95..7f53aa7d4f73d 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -4087,9 +4087,7 @@ bool llvm::foldBranchToCommonDest(BranchInst *BI, DomTreeUpdater *DTU,
 
   Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
 
-  if (!Cond ||
-      (!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond) &&
-       !isa<SelectInst>(Cond)) ||
+  if (!Cond || !isa<CmpInst, BinaryOperator, SelectInst, TruncInst>(Cond) ||
       Cond->getParent() != BB || !Cond->hasOneUse())
     return false;
 
diff --git a/llvm/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll b/llvm/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll
index ffbacc1a89031..95bf296af9b0c 100644
--- a/llvm/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll
+++ b/llvm/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll
@@ -1028,15 +1028,14 @@ define i32 @nodefaultwithholes(i32 %c) {
 ; CHECK-LABEL: @nodefaultwithholes(
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[TMP0:%.*]] = icmp ult i32 [[C:%.*]], 6
-; CHECK-NEXT:    br i1 [[TMP0]], label [[SWITCH_HOLE_CHECK:%.*]], label [[SW_DEFAULT:%.*]]
-; CHECK:       sw.default:
-; CHECK-NEXT:    call void @exit(i32 1)
-; CHECK-NEXT:    unreachable
-; CHECK:       switch.hole_check:
 ; CHECK-NEXT:    [[SWITCH_MASKINDEX:%.*]] = trunc i32 [[C]] to i8
 ; CHECK-NEXT:    [[SWITCH_SHIFTED:%.*]] = lshr i8 47, [[SWITCH_MASKINDEX]]
 ; CHECK-NEXT:    [[SWITCH_LOBIT:%.*]] = trunc i8 [[SWITCH_SHIFTED]] to i1
-; CHECK-NEXT:    br i1 [[SWITCH_LOBIT]], label [[SWITCH_LOOKUP:%.*]], label [[SW_DEFAULT]]
+; CHECK-NEXT:    [[OR_COND:%.*]] = select i1 [[TMP0]], i1 [[SWITCH_LOBIT]], i1 false
+; CHECK-NEXT:    br i1 [[OR_COND]], label [[SWITCH_LOOKUP:%.*]], label [[SW_DEFAULT:%.*]]
+; CHECK:       sw.default:
+; CHECK-NEXT:    call void @exit(i32 1)
+; CHECK-NEXT:    unreachable
 ; CHECK:       switch.lookup:
 ; CHECK-NEXT:    [[SWITCH_GEP:%.*]] = getelementptr inbounds [6 x i32], ptr @switch.table.nodefaultwithholes, i32 0, i32 [[C]]
 ; CHECK-NEXT:    [[SWITCH_LOAD:%.*]] = load i32, ptr [[SWITCH_GEP]], align 4
diff --git a/llvm/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table_big.ll b/llvm/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table_big.ll
index 4ebf09ae3b127..fd6b21a7f9e60 100644
--- a/llvm/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table_big.ll
+++ b/llvm/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table_big.ll
@@ -143,17 +143,16 @@ define i32 @reachable_default_holes_0to31(i32 %x, i32 %y) {
 ; CHECK-LABEL: @reachable_default_holes_0to31(
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[TMP0:%.*]] = icmp ult i32 [[X:%.*]], 32
-; CHECK-NEXT:    br i1 [[TMP0]], label [[SWITCH_HOLE_CHECK:%.*]], label [[RETURN:%.*]]
-; CHECK:       switch.hole_check:
 ; CHECK-NEXT:    [[SWITCH_SHIFTED:%.*]] = lshr i32 -277094665, [[X]]
 ; CHECK-NEXT:    [[SWITCH_LOBIT:%.*]] = trunc i32 [[SWITCH_SHIFTED]] to i1
-; CHECK-NEXT:    br i1 [[SWITCH_LOBIT]], label [[SWITCH_LOOKUP:%.*]], label [[RETURN]]
+; CHECK-NEXT:    [[OR_COND:%.*]] = select i1 [[TMP0]], i1 [[SWITCH_LOBIT]], i1 false
+; CHECK-NEXT:    br i1 [[OR_COND]], label [[SWITCH_LOOKUP:%.*]], label [[RETURN:%.*]]
 ; CHECK:       switch.lookup:
 ; CHECK-NEXT:    [[SWITCH_GEP:%.*]] = getelementptr inbounds [32 x i32], ptr @switch.table.reachable_default_holes_0to31, i32 0, i32 [[X]]
 ; CHECK-NEXT:    [[SWITCH_LOAD:%.*]] = load i32, ptr [[SWITCH_GEP]], align 4
 ; CHECK-NEXT:    br label [[RETURN]]
 ; CHECK:       return:
-; CHECK-NEXT:    [[RES:%.*]] = phi i32 [ [[SWITCH_LOAD]], [[SWITCH_LOOKUP]] ], [ [[Y:%.*]], [[SWITCH_HOLE_CHECK]] ], [ [[Y]], [[ENTRY:%.*]] ]
+; CHECK-NEXT:    [[RES:%.*]] = phi i32 [ [[SWITCH_LOAD]], [[SWITCH_LOOKUP]] ], [ [[Y:%.*]], [[ENTRY:%.*]] ]
 ; CHECK-NEXT:    ret i32 [[RES]]
 ;
 entry:
diff --git a/llvm/test/Transforms/SimplifyCFG/fold-branch-to-common-dest.ll b/llvm/test/Transforms/SimplifyCFG/fold-branch-to-common-dest.ll
index 37f48a9a7e03a..7b88ec338cf5e 100644
--- a/llvm/test/Transforms/SimplifyCFG/fold-branch-to-common-dest.ll
+++ b/llvm/test/Transforms/SimplifyCFG/fold-branch-to-common-dest.ll
@@ -88,10 +88,9 @@ define void @one_pred_trunc_cond(i8 %v0, i8 %v1) {
 ; CHECK-LABEL: @one_pred_trunc_cond(
 ; CHECK-NEXT:  pred:
 ; CHECK-NEXT:    [[C0:%.*]] = icmp eq i8 [[V0:%.*]], 0
-; CHECK-NEXT:    br i1 [[C0]], label [[DISPATCH:%.*]], label [[FINAL_RIGHT:%.*]]
-; CHECK:       dispatch:
 ; CHECK-NEXT:    [[C1:%.*]] = trunc i8 [[V1:%.*]] to i1
-; CHECK-NEXT:    br i1 [[C1]], label [[FINAL_LEFT:%.*]], label [[FINAL_RIGHT]]
+; CHECK-NEXT:    [[OR_COND:%.*]] = select i1 [[C0]], i1 [[C1]], i1 false
+; CHECK-NEXT:    br i1 [[OR_COND]], label [[FINAL_LEFT:%.*]], label [[FINAL_RIGHT:%.*]]
 ; CHECK:       common.ret:
 ; CHECK-NEXT:    ret void
 ; CHECK:       final_left: