[PATCH] D100640: [SimplifyCFG] Skip dbg intrinsics when checking for branch-only BBs.

[Florian Hahn via Phabricator via llvm-commits]

fhahn created this revision.
fhahn added reviewers: reames, spatel, mkazantsev, lebedev.ri.
Herald added a subscriber: hiraditya.
fhahn requested review of this revision.
Herald added a project: LLVM.

Debug intrinsics are free to hoist and should be skipped when looking
for terminator-only blocks. As a consequence, we have to delegate to the
main hoisting loop to hoist any dbg intrinsics instead of jumping to the
terminator case directly.

This fixes PR49982.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D100640

Files:
  llvm/lib/Transforms/Utils/SimplifyCFG.cpp
  llvm/test/Transforms/SimplifyCFG/hoist-dbgvalue.ll


Index: llvm/test/Transforms/SimplifyCFG/hoist-dbgvalue.ll
===================================================================
--- llvm/test/Transforms/SimplifyCFG/hoist-dbgvalue.ll
+++ llvm/test/Transforms/SimplifyCFG/hoist-dbgvalue.ll
@@ -45,8 +45,10 @@
 ; CHECK-LABEL: @hoist_with_debug2(
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[TOBOOL_NOT:%.*]] = icmp ugt i32 [[X:%.*]], 2
-; CHECK-NEXT:    [[P:%.*]] = select i1 [[TOBOOL_NOT]], i1 false, i1 true
-; CHECK-NEXT:    ret i1 [[P]]
+; CHECK-NEXT:    call void @llvm.dbg.value(metadata i32 [[X]], metadata [[META21:![0-9]+]], metadata !DIExpression()), !dbg [[DBG23:![0-9]+]]
+; CHECK-NEXT:    call void @llvm.dbg.value(metadata i32 [[X]], metadata [[META21]], metadata !DIExpression()), !dbg [[DBG23]]
+; CHECK-NEXT:    [[DOT:%.*]] = select i1 [[TOBOOL_NOT]], i1 false, i1 true
+; CHECK-NEXT:    ret i1 [[DOT]]
 ;
 entry:
   %tobool.not = icmp ugt i32 %x, 2
@@ -72,15 +74,11 @@
 ; CHECK-NEXT:    br label [[FOR_COND:%.*]]
 ; CHECK:       for.cond:
 ; CHECK-NEXT:    [[C_0:%.*]] = icmp sgt i32 [[X:%.*]], 0
-; CHECK-NEXT:    br i1 [[C_0]], label [[CHECK:%.*]], label [[LATCH:%.*]]
-; CHECK:       check:
-; CHECK-NEXT:    [[C_1:%.*]] = icmp ugt i32 [[X]], 2
-; CHECK-NEXT:    br label [[EXIT_1:%.*]]
-; CHECK:       latch:
-; CHECK-NEXT:    br i1 [[C_2:%.*]], label [[EXIT_1]], label [[FOR_COND]]
+; CHECK-NEXT:    [[BRMERGE:%.*]] = or i1 [[C_0]], [[C_2:%.*]]
+; CHECK-NEXT:    [[DOTMUX:%.*]] = select i1 [[C_0]], i16 0, i16 20
+; CHECK-NEXT:    br i1 [[BRMERGE]], label [[EXIT_1:%.*]], label [[FOR_COND]]
 ; CHECK:       exit.1:
-; CHECK-NEXT:    [[MERGE:%.*]] = phi i16 [ 20, [[LATCH]] ], [ 0, [[CHECK]] ]
-; CHECK-NEXT:    ret i16 [[MERGE]]
+; CHECK-NEXT:    ret i16 [[DOTMUX]]
 ;
 entry:
   br label %for.cond
Index: llvm/lib/Transforms/Utils/SimplifyCFG.cpp
===================================================================
--- llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -1434,11 +1434,14 @@
   // Check if only hoisting terminators is allowed. This does not add new
   // instructions to the hoist location.
   if (EqTermsOnly) {
-    if (!I1->isIdenticalToWhenDefined(I2))
+    // Skip any debug intrinsics, as they are free to hoist.
+    auto *I1NonDbg = &*skipDebugIntrinsics(I1->getIterator());
+    auto *I2NonDbg = &*skipDebugIntrinsics(I2->getIterator());
+    if (!I1NonDbg->isIdenticalToWhenDefined(I2NonDbg))
       return false;
-    if (!I1->isTerminator())
+    if (!I2NonDbg->isTerminator())
       return false;
-    goto HoistTerminator;
+    // Now we know that we only need to hoist debug instrinsics and the terminator. Let the loop below handle those 2 cases.
   }
 
   do {


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D100640.338061.patch
Type: text/x-patch
Size: 2703 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20210416/eab6885b/attachment.bin>