diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp index 94b0ab892f2dd..1b99908d499e5 100644 --- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp +++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp @@ -286,6 +286,7 @@ class SimplifyCFGOpt { bool simplifyBranch(BranchInst *Branch, IRBuilder<> &Builder); bool simplifyUncondBranch(BranchInst *BI, IRBuilder<> &Builder); bool simplifyCondBranch(BranchInst *BI, IRBuilder<> &Builder); + bool foldCondBranchOnValueKnownInPredecessor(BranchInst *BI); bool tryToSimplifyUncondBranchWithICmpInIt(ICmpInst *ICI, IRBuilder<> &Builder); @@ -3604,15 +3605,19 @@ foldCondBranchOnValueKnownInPredecessorImpl(BranchInst *BI, DomTreeUpdater *DTU, return false; } -static bool foldCondBranchOnValueKnownInPredecessor(BranchInst *BI, - DomTreeUpdater *DTU, - const DataLayout &DL, - AssumptionCache *AC) { +bool SimplifyCFGOpt::foldCondBranchOnValueKnownInPredecessor(BranchInst *BI) { + // Note: If BB is a loop header then there is a risk that threading introduces + // a non-canonical loop by moving a back edge. So we avoid this optimization + // for loop headers if NeedCanonicalLoop is set. + if (Options.NeedCanonicalLoop && is_contained(LoopHeaders, BI->getParent())) + return false; + std::optional Result; bool EverChanged = false; do { // Note that None means "we changed things, but recurse further." - Result = foldCondBranchOnValueKnownInPredecessorImpl(BI, DTU, DL, AC); + Result = + foldCondBranchOnValueKnownInPredecessorImpl(BI, DTU, DL, Options.AC); EverChanged |= Result == std::nullopt || *Result; } while (Result == std::nullopt); return EverChanged; @@ -8030,7 +8035,7 @@ bool SimplifyCFGOpt::simplifyCondBranch(BranchInst *BI, IRBuilder<> &Builder) { // If this is a branch on something for which we know the constant value in // predecessors (e.g. a phi node in the current block), thread control // through this block. - if (foldCondBranchOnValueKnownInPredecessor(BI, DTU, DL, Options.AC)) + if (foldCondBranchOnValueKnownInPredecessor(BI)) return requestResimplify(); // Scan predecessor blocks for conditional branches. diff --git a/llvm/test/CodeGen/ARM/2013-05-05-IfConvertBug.ll b/llvm/test/CodeGen/ARM/2013-05-05-IfConvertBug.ll index 344bb15d2a8b8..8f798fac06f54 100644 --- a/llvm/test/CodeGen/ARM/2013-05-05-IfConvertBug.ll +++ b/llvm/test/CodeGen/ARM/2013-05-05-IfConvertBug.ll @@ -1,7 +1,7 @@ ; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py -; RUN: llc < %s -mtriple=thumbv7-apple-ios -mcpu=cortex-a8 | FileCheck %s -; RUN: llc < %s -mtriple=thumbv8 | FileCheck -check-prefix=CHECK-V8 %s -; RUN: llc < %s -mtriple=thumbv7 -arm-restrict-it | FileCheck -check-prefix=CHECK-RESTRICT-IT %s +; RUN: llc -keep-loops="false" < %s -mtriple=thumbv7-apple-ios -mcpu=cortex-a8 | FileCheck %s +; RUN: llc -keep-loops="false" < %s -mtriple=thumbv8 | FileCheck -check-prefix=CHECK-V8 %s +; RUN: llc -keep-loops="false" < %s -mtriple=thumbv7 -arm-restrict-it | FileCheck -check-prefix=CHECK-RESTRICT-IT %s define i32 @t1(i32 %a, i32 %b, ptr %retaddr) { ; CHECK-LABEL: t1: diff --git a/llvm/test/Transforms/SimplifyCFG/2008-07-13-InfLoopMiscompile.ll b/llvm/test/Transforms/SimplifyCFG/2008-07-13-InfLoopMiscompile.ll index 2e9e7b19c73e2..44d92e1a1c210 100644 --- a/llvm/test/Transforms/SimplifyCFG/2008-07-13-InfLoopMiscompile.ll +++ b/llvm/test/Transforms/SimplifyCFG/2008-07-13-InfLoopMiscompile.ll @@ -1,5 +1,5 @@ ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py -; RUN: opt < %s -passes=simplifycfg -simplifycfg-require-and-preserve-domtree=1 -S | FileCheck %s +; RUN: opt < %s -passes=simplifycfg -simplifycfg-require-and-preserve-domtree=1 -keep-loops="false" -S | FileCheck %s ; PR2540 ; Outval should end up with a select from 0/2, not all constants. @@ -52,4 +52,3 @@ func_1.exit: ; preds = %cowblock, %entry } declare i32 @printf(ptr, ...) nounwind - diff --git a/llvm/test/Transforms/SimplifyCFG/2025-07-29-non-canoncial-loop.ll b/llvm/test/Transforms/SimplifyCFG/2025-07-29-non-canoncial-loop.ll new file mode 100644 index 0000000000000..322dd98f48df1 --- /dev/null +++ b/llvm/test/Transforms/SimplifyCFG/2025-07-29-non-canoncial-loop.ll @@ -0,0 +1,62 @@ +; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5 +; RUN: opt < %s -passes=simplifycfg -simplifycfg-require-and-preserve-domtree=1 --keep-loops="true" -S | FileCheck --check-prefix=NO-THREADING %s +; Checks that we do not thread the control flow through the loop header loop_header as +; that will introduce a non-canonical loop. + +; RUN: opt < %s -passes=simplifycfg -simplifycfg-require-and-preserve-domtree=1 --keep-loops="false" -S | FileCheck --check-prefix=THREADING %s +; Checks that we thread the control flow through the loop header loop_header since we +; do not request --keep-loops. + +define void @__start(i1 %cond) { +; NO-THREADING-LABEL: define void @__start( +; NO-THREADING-SAME: i1 [[COND:%.*]]) { +; NO-THREADING-NEXT: [[ENTRY:.*:]] +; NO-THREADING-NEXT: br label %[[LOOP_HEADER:.*]] +; NO-THREADING: [[LOOP_HEADER]]: +; NO-THREADING-NEXT: br i1 [[COND]], label %[[LOOP_BODY_1:.*]], label %[[LOOP_BODY_0:.*]] +; NO-THREADING: [[LOOP_BODY_0]]: +; NO-THREADING-NEXT: [[_0_:%.*]] = add i16 0, 0 +; NO-THREADING-NEXT: br label %[[LOOP_EXIT:.*]] +; NO-THREADING: [[LOOP_BODY_1]]: +; NO-THREADING-NEXT: [[_1_:%.*]] = add i32 0, 1 +; NO-THREADING-NEXT: br label %[[LOOP_EXIT]] +; NO-THREADING: [[LOOP_EXIT]]: +; NO-THREADING-NEXT: br i1 [[COND]], label %[[LOOP_HEADER]], label %[[EXIT:.*]] +; NO-THREADING: [[EXIT]]: +; NO-THREADING-NEXT: ret void +; +; THREADING-LABEL: define void @__start( +; THREADING-SAME: i1 [[COND:%.*]]) { +; THREADING-NEXT: [[ENTRY:.*:]] +; THREADING-NEXT: br i1 [[COND]], label %[[LOOP_BODY_1:.*]], label %[[LOOP_BODY_0:.*]] +; THREADING: [[LOOP_BODY_0]]: +; THREADING-NEXT: [[_0_:%.*]] = add i16 0, 0 +; THREADING-NEXT: br label %[[LOOP_EXIT:.*]] +; THREADING: [[LOOP_BODY_1]]: +; THREADING-NEXT: [[_1_:%.*]] = add i32 0, 1 +; THREADING-NEXT: br label %[[LOOP_EXIT]] +; THREADING: [[LOOP_EXIT]]: +; THREADING-NEXT: br i1 [[COND]], label %[[LOOP_BODY_1]], label %[[EXIT:.*]] +; THREADING: [[EXIT]]: +; THREADING-NEXT: ret void +; +entry: + br label %loop_header + +loop_header: ; preds = %loop_exit, %entry + br i1 %cond, label %loop_body_1, label %loop_body_0 + +loop_body_0: ; preds = %loop_header + %_0_ = add i16 0, 0 + br label %loop_exit + +loop_body_1: ; preds = %loop_header + %_1_ = add i32 0, 1 + br label %loop_exit + +loop_exit: ; preds = %loop_body_1, %loop_body_0 + br i1 %cond, label %loop_header, label %exit + +exit: ; preds = %loop_exit + ret void +} diff --git a/llvm/test/Transforms/SimplifyCFG/branch-phi-thread.ll b/llvm/test/Transforms/SimplifyCFG/branch-phi-thread.ll index 0afec05ecbd6a..ec9423bd81675 100644 --- a/llvm/test/Transforms/SimplifyCFG/branch-phi-thread.ll +++ b/llvm/test/Transforms/SimplifyCFG/branch-phi-thread.ll @@ -1,5 +1,5 @@ ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py -; RUN: opt < %s -passes=simplifycfg,adce -simplifycfg-require-and-preserve-domtree=1 -S | FileCheck %s +; RUN: opt < %s -passes=simplifycfg,adce -simplifycfg-require-and-preserve-domtree=1 -keep-loops="false" -S | FileCheck %s declare void @f1() diff --git a/llvm/test/Transforms/SimplifyCFG/jump-threading.ll b/llvm/test/Transforms/SimplifyCFG/jump-threading.ll index 50a32413a0551..a4073ae6eb0b4 100644 --- a/llvm/test/Transforms/SimplifyCFG/jump-threading.ll +++ b/llvm/test/Transforms/SimplifyCFG/jump-threading.ll @@ -1,5 +1,5 @@ ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py -; RUN: opt -S -passes=simplifycfg < %s | FileCheck %s +; RUN: opt -S -passes=simplifycfg -keep-loops="false" < %s | FileCheck %s declare void @foo() declare void @bar() diff --git a/llvm/test/Transforms/SimplifyCFG/two-entry-phi-return.ll b/llvm/test/Transforms/SimplifyCFG/two-entry-phi-return.ll index 57930c91b9796..f6d71ddda74fe 100644 --- a/llvm/test/Transforms/SimplifyCFG/two-entry-phi-return.ll +++ b/llvm/test/Transforms/SimplifyCFG/two-entry-phi-return.ll @@ -1,5 +1,5 @@ ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py -; RUN: opt < %s -passes=simplifycfg -simplifycfg-require-and-preserve-domtree=1 -S | FileCheck %s +; RUN: opt < %s -passes=simplifycfg -simplifycfg-require-and-preserve-domtree=1 -keep-loops="false" -S | FileCheck %s define i1 @qux(ptr %m, ptr %n, ptr %o, ptr %p) nounwind { ; CHECK-LABEL: @qux(