[MergeICmp] Fix a bug in entry block shuffled to middle of the chain

[trentxintong]

Summary

Fix a bug in entry block shuffled to middle of the chain.

[courbet]

Thanks for the fix.

lib/Transforms/Scalar/MergeICmps.cpp

406 ↗

(On Diff #138980)

s/./,/

llvm/trunk/lib/Transforms/Scalar/MergeICmps.cpp

bool BCECmpChain::simplify(const TargetLibraryInfo *const TLI) {
   }
 
   // Remove phi references to comparison blocks, they will be rebuilt as we
   // merge the blocks.
   for (const auto &Comparison : Comparisons_) {
     Phi_.removeIncomingValue(Comparison.BB, false);
   }
 
+  // If entry block is part of the chain, we need to make the first block
+  // of the chain the new entry block of the function.
+  BasicBlock *Entry = &Comparisons_[0].BB->getParent()->getEntryBlock();
+  for (size_t I = 1; I < Comparisons_.size(); ++I) {
+    if (Entry == Comparisons_[I].BB) {
+      BasicBlock *NEntryBB = BasicBlock::Create(Entry->getContext(), "",
+                                                Entry->getParent(), Entry);
+      BranchInst::Create(Entry, NEntryBB);
+    }
+  }
+
   // Point the predecessors of the chain to the first comparison block (which is
   // the new entry point).
   if (EntryBlock_ != Comparisons_[0].BB)
     EntryBlock_->replaceAllUsesWith(Comparisons_[0].BB);
 
   // Effectively merge blocks.
   int NumMerged = 1;
   for (size_t I = 1; I < Comparisons_.size(); ++I) {

llvm/trunk/test/Transforms/MergeICmps/X86/entry-block-shuffled.ll

+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -mergeicmps -mtriple=x86_64-unknown-unknown -S | FileCheck %s
+
+%"struct.std::pair" = type { i32, i32, i32, i32 }
+
+; The entry block is part of the chain. It however can not be merged. We need to make the
+; first comparison block in the chain the new entry block of the function.
+
+define zeroext i1 @opeq1(
+; CHECK-LABEL: @opeq1(
+; CHECK-NEXT:    br label [[LAND_RHS_I:%.*]]
+; CHECK:       land.rhs.i:
+; CHECK-NEXT:    [[SECOND_I:%.*]] = getelementptr inbounds %"struct.std::pair", %"struct.std::pair"* %a, i64 0, i32 0 
+; CHECK-NEXT:    [[SECOND2_I:%.*]] = getelementptr inbounds %"struct.std::pair", %"struct.std::pair"* %b, i64 0, i32 0
+; CHECK-NEXT:    [[CSTR:%.*]] = bitcast i32* [[SECOND_I]] to i8*
+; CHECK-NEXT:    [[CSTR1:%.*]] = bitcast i32* [[SECOND2_I]] to i8*
+; CHECK-NEXT:    [[MEMCMP:%.*]] = call i32 @memcmp(i8* [[CSTR]], i8* [[CSTR1]], i64 8)
+;
+  %"struct.std::pair"* nocapture readonly dereferenceable(16) %a,
+  %"struct.std::pair"* nocapture readonly dereferenceable(16) %b) local_unnamed_addr #0 {
+entry:
+  %first.i = getelementptr inbounds %"struct.std::pair", %"struct.std::pair"* %a, i64 0, i32 3 
+  %0 = load i32, i32* %first.i, align 4
+  %first1.i = getelementptr inbounds %"struct.std::pair", %"struct.std::pair"* %b, i64 0, i32 2 
+  %1 = load i32, i32* %first1.i, align 4
+  %cmp.i = icmp eq i32 %0, %1
+  br i1 %cmp.i, label %land.rhs.i, label %opeq1.exit
+
+land.rhs.i:
+  %second.i = getelementptr inbounds %"struct.std::pair", %"struct.std::pair"* %a, i64 0, i32 0
+  %2 = load i32, i32* %second.i, align 4
+  %second2.i = getelementptr inbounds %"struct.std::pair", %"struct.std::pair"* %b, i64 0, i32 0
+  %3 = load i32, i32* %second2.i, align 4
+  %cmp3.i = icmp eq i32 %2, %3
+  br i1 %cmp3.i, label %land.rhs.i.2, label %opeq1.exit
+
+land.rhs.i.2:
+  %third.i = getelementptr inbounds %"struct.std::pair", %"struct.std::pair"* %a, i64 0, i32 1 
+  %4 = load i32, i32* %third.i, align 4
+  %third2.i = getelementptr inbounds %"struct.std::pair", %"struct.std::pair"* %b, i64 0, i32 1
+  %5 = load i32, i32* %third2.i, align 4
+  %cmp4.i = icmp eq i32 %4, %5
+  br i1 %cmp4.i, label %land.rhs.i.3, label %opeq1.exit
+
+land.rhs.i.3:
+  %fourth.i = getelementptr inbounds %"struct.std::pair", %"struct.std::pair"* %a, i64 0, i32 3 
+  %6 = load i32, i32* %fourth.i, align 4
+  %fourth2.i = getelementptr inbounds %"struct.std::pair", %"struct.std::pair"* %b, i64 0, i32 3
+  %7 = load i32, i32* %fourth2.i, align 4
+  %cmp5.i = icmp eq i32 %6, %7
+  br label %opeq1.exit
+
+opeq1.exit:
+  %8 = phi i1 [ false, %entry ], [ false,  %land.rhs.i], [ false, %land.rhs.i.2 ], [ %cmp5.i, %land.rhs.i.3 ]
+  ret i1 %8
+}

llvm/trunk/test/Transforms/MergeICmps/X86/pair-int32-int32.ll

 ; The two 4 byte loads and compares are replaced with a single 8-byte memcmp.
 ; The branch is now a direct branch; the other block has been removed.
 ; The phi is updated.
 }
 
 ; Same as above, but the two blocks are in inverse order.
 define zeroext i1 @opeq1_inverse(
 ; X86-LABEL: @opeq1_inverse(
-; X86-NEXT:  land.rhs.i:
+; X86-NEXT:    br label [[LAND_RHS_I:%.*]]
+; X86:       land.rhs.i:
 ; X86-NEXT:    [[SECOND_I:%.*]] = getelementptr inbounds %"struct.std::pair", %"struct.std::pair"* [[A:%.*]], i64 0, i32 0
 ; X86-NEXT:    [[SECOND2_I:%.*]] = getelementptr inbounds %"struct.std::pair", %"struct.std::pair"* [[B:%.*]], i64 0, i32 0
 ; X86-NEXT:    [[CSTR:%.*]] = bitcast i32* [[SECOND_I]] to i8*
 ; X86-NEXT:    [[CSTR1:%.*]] = bitcast i32* [[SECOND2_I]] to i8*
 ; X86-NEXT:    [[MEMCMP:%.*]] = call i32 @memcmp(i8* [[CSTR]], i8* [[CSTR1]], i64 8)
 ; X86-NEXT:    [[TMP0:%.*]] = icmp eq i32 [[MEMCMP]], 0
 ; X86-NEXT:    br label [[OPEQ1_EXIT:%.*]]
 ; X86:       opeq1.exit: