[InstCombine] Combine const GEP chains

[dtcxzyw]

Summary

This patch reverts rGae739aefd7473517d3f08b5c8d08a66c7f469198 to address performance regressions reported by our CI after rG2ec1d0f427c7822540352c0c14d057e7bfe4f77b.

For example:

define ptr @const_gep_chain(ptr %p, i64 %a) {
    %p1 = getelementptr inbounds i8, ptr %p, i64 %a
    %p2 = getelementptr inbounds i8, ptr %p1, i64 1
    %p3 = getelementptr inbounds i8, ptr %p2, i64 2
    %p4 = getelementptr inbounds i8, ptr %p3, i64 3
    ret ptr %p4
}

The last three GEPs will not be folded since rG2ec1d0f427c7822540352c0c14d057e7bfe4f77b.

I think it is appropriate to remove this code because there is no compile-time regression reported in our benchmarks.

[nikic]

LGTM. If we need to bring this check back, it will need a stronger condition.

[dtcxzyw]

Update tests

[nikic]

llvm/test/Transforms/LoopVectorize/AArch64/vector-reverse-mask4.ll

1

What's going on with the test changes in this file? I don't really get how this patch could cause them.

[dtcxzyw]

Update tests

[dtcxzyw]

llvm/test/Transforms/LoopVectorize/AArch64/vector-reverse-mask4.ll

1

Sorry, I just forgot to build the AArch64 target.

[nikic]

llvm/test/Transforms/LoopVectorize/consecutive-ptr-uniforms.ll

454

Would it be enough to only update these two lines in this test, rather than delete the whole block?

[dtcxzyw]

Update tests

[nikic]

LGTM

[nikic]

Do you have commit access? If not, can you let me know the Name <email> to use for the commit?

[dtcxzyw]

Resolve conflicts before committing

llvm/lib/Transforms/InstCombine/InstructionCombining.cpp

 Instruction *InstCombinerImpl::visitGEPOfGEP(GetElementPtrInst &GEP,
                                              GEPOperator *Src) {
   // Combine Indices - If the source pointer to this getelementptr instruction
   // is a getelementptr instruction with matching element type, combine the
   // indices of the two getelementptr instructions into a single instruction.
   if (!shouldMergeGEPs(*cast<GEPOperator>(&GEP), *Src))
     return nullptr;
 
-  // Note that if our source is a gep chain itself then we wait for that
-  // chain to be resolved before we perform this transformation.  This
-  // avoids us creating a TON of code in some cases.
-  if (auto *SrcGEP = dyn_cast<GEPOperator>(Src->getOperand(0)))
-    if (SrcGEP->getNumOperands() == 2 && shouldMergeGEPs(*Src, *SrcGEP))
-      return nullptr;   // Wait until our source is folded to completion.
-
   // For constant GEPs, use a more general offset-based folding approach.
   Type *PtrTy = Src->getType()->getScalarType();
   if (GEP.hasAllConstantIndices() &&
       (Src->hasOneUse() || Src->hasAllConstantIndices())) {
     // Split Src into a variable part and a constant suffix.
     gep_type_iterator GTI = gep_type_begin(*Src);
     Type *BaseType = GTI.getIndexedType();
     bool IsFirstType = true;

llvm/test/Transforms/InstCombine/getelementptr.ll

 
 define ptr @const_gep_0xi8_global() {
 ; CHECK-LABEL: @const_gep_0xi8_global(
 ; CHECK-NEXT:    ret ptr getelementptr ([0 x i8], ptr @g_0xi8_e, i64 0, i64 10)
 ;
   ret ptr getelementptr ([0 x i8], ptr @g_0xi8_e, i64 0, i64 10)
 }
 
+define ptr @const_gep_chain(ptr %p, i64 %a) {
+; CHECK-LABEL: @const_gep_chain(
+; CHECK-NEXT:    [[P1:%.*]] = getelementptr inbounds i8, ptr [[P:%.*]], i64 [[A:%.*]]
+; CHECK-NEXT:    [[P4:%.*]] = getelementptr inbounds i8, ptr [[P1]], i64 6
+; CHECK-NEXT:    ret ptr [[P4]]
+;
+  %p1 = getelementptr inbounds i8, ptr %p, i64 %a
+  %p2 = getelementptr inbounds i8, ptr %p1, i64 1
+  %p3 = getelementptr inbounds i8, ptr %p2, i64 2
+  %p4 = getelementptr inbounds i8, ptr %p3, i64 3
+  ret ptr %p4
+}
+
 !0 = !{!"branch_weights", i32 2, i32 10}

llvm/test/Transforms/LoopVectorize/AArch64/vector-reverse-mask4.ll

 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
 ; This is the loop in c++ being vectorize in this file with
 ; shuffle reverse
 
 ;#pragma clang loop vectorize_width(4, fixed)
 ;  for (long int i = N - 1; i >= 0; i--)
 ;  {
 ;    if (cond[i])
 ;      a[i] += 1;

 ; CHECK:       vector.body:
 ; CHECK-NEXT:    [[INDEX:%.*]] = phi i64 [ 0, [[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], [[VECTOR_BODY]] ]
 ; CHECK-NEXT:    [[TMP0:%.*]] = xor i64 [[INDEX]], -1
 ; CHECK-NEXT:    [[TMP1:%.*]] = add i64 [[TMP0]], [[N]]
 ; CHECK-NEXT:    [[TMP2:%.*]] = getelementptr inbounds double, ptr [[COND:%.*]], i64 [[TMP1]]
 ; CHECK-NEXT:    [[TMP3:%.*]] = getelementptr inbounds double, ptr [[TMP2]], i64 -3
 ; CHECK-NEXT:    [[WIDE_LOAD:%.*]] = load <4 x double>, ptr [[TMP3]], align 8
 ; CHECK-NEXT:    [[REVERSE:%.*]] = shufflevector <4 x double> [[WIDE_LOAD]], <4 x double> poison, <4 x i32> <i32 3, i32 2, i32 1, i32 0>
-; CHECK-NEXT:    [[TMP5:%.*]] = getelementptr inbounds double, ptr [[TMP2]], i64 -4
-; CHECK-NEXT:    [[TMP6:%.*]] = getelementptr inbounds double, ptr [[TMP5]], i64 -3
-; CHECK-NEXT:    [[WIDE_LOAD1:%.*]] = load <4 x double>, ptr [[TMP6]], align 8
+; CHECK-NEXT:    [[TMP4:%.*]] = getelementptr inbounds double, ptr [[TMP2]], i64 -7
+; CHECK-NEXT:    [[WIDE_LOAD1:%.*]] = load <4 x double>, ptr [[TMP4]], align 8
 ; CHECK-NEXT:    [[REVERSE2:%.*]] = shufflevector <4 x double> [[WIDE_LOAD1]], <4 x double> poison, <4 x i32> <i32 3, i32 2, i32 1, i32 0>
-; CHECK-NEXT:    [[TMP8:%.*]] = fcmp une <4 x double> [[REVERSE]], zeroinitializer
-; CHECK-NEXT:    [[TMP9:%.*]] = fcmp une <4 x double> [[REVERSE2]], zeroinitializer
-; CHECK-NEXT:    [[TMP10:%.*]] = getelementptr double, ptr [[A:%.*]], i64 [[TMP1]]
-; CHECK-NEXT:    [[TMP11:%.*]] = getelementptr double, ptr [[TMP10]], i64 -3
-; CHECK-NEXT:    [[REVERSE3:%.*]] = shufflevector <4 x i1> [[TMP8]], <4 x i1> poison, <4 x i32> <i32 3, i32 2, i32 1, i32 0>
-; CHECK-NEXT:    [[WIDE_MASKED_LOAD:%.*]] = call <4 x double> @llvm.masked.load.v4f64.p0(ptr [[TMP11]], i32 8, <4 x i1> [[REVERSE3]], <4 x double> poison)
-; CHECK-NEXT:    [[TMP13:%.*]] = getelementptr double, ptr [[TMP10]], i64 -4
-; CHECK-NEXT:    [[TMP14:%.*]] = getelementptr double, ptr [[TMP13]], i64 -3
-; CHECK-NEXT:    [[REVERSE5:%.*]] = shufflevector <4 x i1> [[TMP9]], <4 x i1> poison, <4 x i32> <i32 3, i32 2, i32 1, i32 0>
-; CHECK-NEXT:    [[WIDE_MASKED_LOAD6:%.*]] = call <4 x double> @llvm.masked.load.v4f64.p0(ptr [[TMP14]], i32 8, <4 x i1> [[REVERSE5]], <4 x double> poison)
-; CHECK-NEXT:    [[TMP16:%.*]] = fadd <4 x double> [[WIDE_MASKED_LOAD]], <double 1.000000e+00, double 1.000000e+00, double 1.000000e+00, double 1.000000e+00>
-; CHECK-NEXT:    [[TMP17:%.*]] = fadd <4 x double> [[WIDE_MASKED_LOAD6]], <double 1.000000e+00, double 1.000000e+00, double 1.000000e+00, double 1.000000e+00>
-; CHECK-NEXT:    call void @llvm.masked.store.v4f64.p0(<4 x double> [[TMP16]], ptr [[TMP11]], i32 8, <4 x i1> [[REVERSE3]])
-; CHECK-NEXT:    call void @llvm.masked.store.v4f64.p0(<4 x double> [[TMP17]], ptr [[TMP14]], i32 8, <4 x i1> [[REVERSE5]])
+; CHECK-NEXT:    [[TMP5:%.*]] = fcmp une <4 x double> [[REVERSE]], zeroinitializer
+; CHECK-NEXT:    [[TMP6:%.*]] = fcmp une <4 x double> [[REVERSE2]], zeroinitializer
+; CHECK-NEXT:    [[TMP7:%.*]] = getelementptr double, ptr [[A:%.*]], i64 [[TMP1]]
+; CHECK-NEXT:    [[TMP8:%.*]] = getelementptr double, ptr [[TMP7]], i64 -3
+; CHECK-NEXT:    [[REVERSE3:%.*]] = shufflevector <4 x i1> [[TMP5]], <4 x i1> poison, <4 x i32> <i32 3, i32 2, i32 1, i32 0>
+; CHECK-NEXT:    [[WIDE_MASKED_LOAD:%.*]] = call <4 x double> @llvm.masked.load.v4f64.p0(ptr [[TMP8]], i32 8, <4 x i1> [[REVERSE3]], <4 x double> poison)
+; CHECK-NEXT:    [[TMP9:%.*]] = getelementptr double, ptr [[TMP7]], i64 -7
+; CHECK-NEXT:    [[REVERSE5:%.*]] = shufflevector <4 x i1> [[TMP6]], <4 x i1> poison, <4 x i32> <i32 3, i32 2, i32 1, i32 0>
+; CHECK-NEXT:    [[WIDE_MASKED_LOAD6:%.*]] = call <4 x double> @llvm.masked.load.v4f64.p0(ptr [[TMP9]], i32 8, <4 x i1> [[REVERSE5]], <4 x double> poison)
+; CHECK-NEXT:    [[TMP10:%.*]] = fadd <4 x double> [[WIDE_MASKED_LOAD]], <double 1.000000e+00, double 1.000000e+00, double 1.000000e+00, double 1.000000e+00>
+; CHECK-NEXT:    [[TMP11:%.*]] = fadd <4 x double> [[WIDE_MASKED_LOAD6]], <double 1.000000e+00, double 1.000000e+00, double 1.000000e+00, double 1.000000e+00>
+; CHECK-NEXT:    call void @llvm.masked.store.v4f64.p0(<4 x double> [[TMP10]], ptr [[TMP8]], i32 8, <4 x i1> [[REVERSE3]])
+; CHECK-NEXT:    call void @llvm.masked.store.v4f64.p0(<4 x double> [[TMP11]], ptr [[TMP9]], i32 8, <4 x i1> [[REVERSE5]])
 ; CHECK-NEXT:    [[INDEX_NEXT]] = add nuw i64 [[INDEX]], 8
-; CHECK-NEXT:    [[TMP20:%.*]] = icmp eq i64 [[INDEX_NEXT]], [[N_VEC]]
-; CHECK-NEXT:    br i1 [[TMP20]], label [[MIDDLE_BLOCK:%.*]], label [[VECTOR_BODY]], !llvm.loop [[LOOP0:![0-9]+]]
+; CHECK-NEXT:    [[TMP12:%.*]] = icmp eq i64 [[INDEX_NEXT]], [[N_VEC]]
+; CHECK-NEXT:    br i1 [[TMP12]], label [[MIDDLE_BLOCK:%.*]], label [[VECTOR_BODY]], !llvm.loop [[LOOP0:![0-9]+]]
 ; CHECK:       middle.block:
 ; CHECK-NEXT:    [[CMP_N:%.*]] = icmp eq i64 [[N_VEC]], [[N]]
 ; CHECK-NEXT:    br i1 [[CMP_N]], label [[FOR_COND_CLEANUP_LOOPEXIT:%.*]], label [[SCALAR_PH]]
 ; CHECK:       scalar.ph:
 ; CHECK-NEXT:    [[BC_RESUME_VAL:%.*]] = phi i64 [ [[IND_END]], [[MIDDLE_BLOCK]] ], [ [[N]], [[FOR_BODY_PREHEADER]] ]
 ; CHECK-NEXT:    br label [[FOR_BODY:%.*]]
 ; CHECK:       for.cond.cleanup.loopexit:
 ; CHECK-NEXT:    br label [[FOR_COND_CLEANUP]]
 ; CHECK:       for.cond.cleanup:
 ; CHECK-NEXT:    ret void
 ; CHECK:       for.body:
 ; CHECK-NEXT:    [[I_08_IN:%.*]] = phi i64 [ [[I_08:%.*]], [[FOR_INC:%.*]] ], [ [[BC_RESUME_VAL]], [[SCALAR_PH]] ]
 ; CHECK-NEXT:    [[I_08]] = add nsw i64 [[I_08_IN]], -1
 ; CHECK-NEXT:    [[ARRAYIDX:%.*]] = getelementptr inbounds double, ptr [[COND]], i64 [[I_08]]
-; CHECK-NEXT:    [[TMP21:%.*]] = load double, ptr [[ARRAYIDX]], align 8
-; CHECK-NEXT:    [[TOBOOL:%.*]] = fcmp une double [[TMP21]], 0.000000e+00
+; CHECK-NEXT:    [[TMP13:%.*]] = load double, ptr [[ARRAYIDX]], align 8
+; CHECK-NEXT:    [[TOBOOL:%.*]] = fcmp une double [[TMP13]], 0.000000e+00
 ; CHECK-NEXT:    br i1 [[TOBOOL]], label [[IF_THEN:%.*]], label [[FOR_INC]]
 ; CHECK:       if.then:
 ; CHECK-NEXT:    [[ARRAYIDX1:%.*]] = getelementptr inbounds double, ptr [[A]], i64 [[I_08]]
-; CHECK-NEXT:    [[TMP22:%.*]] = load double, ptr [[ARRAYIDX1]], align 8
-; CHECK-NEXT:    [[ADD:%.*]] = fadd double [[TMP22]], 1.000000e+00
+; CHECK-NEXT:    [[TMP14:%.*]] = load double, ptr [[ARRAYIDX1]], align 8
+; CHECK-NEXT:    [[ADD:%.*]] = fadd double [[TMP14]], 1.000000e+00
 ; CHECK-NEXT:    store double [[ADD]], ptr [[ARRAYIDX1]], align 8
 ; CHECK-NEXT:    br label [[FOR_INC]]
 ; CHECK:       for.inc:
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt i64 [[I_08_IN]], 1
-; CHECK-NEXT:    br i1 [[CMP]], label [[FOR_BODY]], label [[FOR_COND_CLEANUP_LOOPEXIT]], !llvm.loop [[LOOP3:![0-9]+]]
+; CHECK-NEXT:    br i1 [[CMP]], label [[FOR_BODY]], label [[FOR_COND_CLEANUP_LOOPEXIT]], !llvm.loop [[LOOP4:![0-9]+]]
 ;
 
 entry:
   %cmp7 = icmp sgt i64 %N, 0
   br i1 %cmp7, label %for.body, label %for.cond.cleanup
 
 for.cond.cleanup:                                 ; preds = %for.cond.cleanup, %entry
   ret void

llvm/test/Transforms/LoopVectorize/consecutive-ptr-uniforms.ll

 ; INTER-NEXT:  LV: Found uniform instruction: %tmp6 = getelementptr inbounds i8, ptr %B, i64 %i
 ; INTER-NEXT:  LV: Found uniform instruction: %tmp0 = getelementptr inbounds i64, ptr %A, i64 %i
 ; INTER-NEXT:  LV: Found uniform instruction: %i = phi i64 [ 0, %entry ], [ %i.next, %for.body ]
 ; INTER-NEXT:  LV: Found uniform instruction: %i.next = add nuw nsw i64 %i, 1
 ; INTER:       define void @pointer_operand_geps_with_different_indexed_types(
 ; INTER:       vector.body:
 ; INTER-NEXT:    [[INDEX:%.*]] = phi i64 [ 0, %vector.ph ], [ [[INDEX_NEXT:%.*]], %vector.body ]
 ; INTER-NEXT:    [[TMP4:%.*]] = getelementptr inbounds i64, ptr %A, i64 [[INDEX]]
-; INTER-NEXT:    [[TMP5:%.*]] = getelementptr inbounds i8, ptr [[TMP4]], i64 3
-; INTER-NEXT:    [[TMP6:%.*]] = getelementptr inbounds i8, ptr [[TMP5]], i64 -3
-; INTER-NEXT:    [[WIDE_VEC:%.*]] = load <32 x i8>, ptr [[TMP6]], align 1
+; INTER-NEXT:    [[WIDE_VEC:%.*]] = load <32 x i8>, ptr [[TMP4]], align 1
 ; INTER-NEXT:    [[STRIDED_VEC:%.*]] = shufflevector <32 x i8> [[WIDE_VEC]], <32 x i8> poison, <4 x i32> <i32 0, i32 8, i32 16, i32 24>
-; INTER-NEXT:    [[STRIDED_VEC5:%.*]] = shufflevector <32 x i8> [[WIDE_VEC]], <32 x i8> poison, <4 x i32> <i32 3, i32 11, i32 19, i32 27>
-; INTER-NEXT:    [[TMP6:%.*]] = xor <4 x i8> [[STRIDED_VEC5]], [[STRIDED_VEC]]
-; INTER-NEXT:    [[TMP7:%.*]] = getelementptr inbounds i8, ptr %B, i64 [[INDEX]]
-; INTER-NEXT:    store <4 x i8> [[TMP6]], ptr [[TMP7]], align 1
+; INTER-NEXT:    [[STRIDED_VEC3:%.*]] = shufflevector <32 x i8> [[WIDE_VEC]], <32 x i8> poison, <4 x i32> <i32 3, i32 11, i32 19, i32 27>
+; INTER-NEXT:    [[TMP5:%.*]] = xor <4 x i8> [[STRIDED_VEC3]], [[STRIDED_VEC]]
+; INTER-NEXT:    [[TMP6:%.*]] = getelementptr inbounds i8, ptr %B, i64 [[INDEX]]
+; INTER-NEXT:    store <4 x i8> [[TMP5]], ptr [[TMP6]], align 1
 ; INTER-NEXT:    [[INDEX_NEXT]] = add nuw i64 [[INDEX]], 4
 ; INTER:         br i1 {{.*}}, label %middle.block, label %vector.body
 ;
 define void @pointer_operand_geps_with_different_indexed_types(i64* %A, i8* %B, i64 %n) {
 entry:
   br label %for.body
 
 for.body:

llvm/test/Transforms/LoopVectorize/interleaved-accesses.ll

 ; CHECK-NEXT:    [[VEC_IND:%.*]] = phi <4 x i32> [ <i32 0, i32 1, i32 2, i32 3>, [[VECTOR_PH]] ], [ [[VEC_IND_NEXT:%.*]], [[VECTOR_BODY]] ]
 ; CHECK-NEXT:    [[TMP0:%.*]] = mul i64 [[INDEX]], 12
 ; CHECK-NEXT:    [[NEXT_GEP:%.*]] = getelementptr i8, ptr [[A:%.*]], i64 [[TMP0]]
 ; CHECK-NEXT:    [[WIDE_VEC:%.*]] = load <12 x i32>, ptr [[NEXT_GEP]], align 4
 ; CHECK-NEXT:    [[STRIDED_VEC:%.*]] = shufflevector <12 x i32> [[WIDE_VEC]], <12 x i32> poison, <4 x i32> <i32 0, i32 3, i32 6, i32 9>
 ; CHECK-NEXT:    [[STRIDED_VEC2:%.*]] = shufflevector <12 x i32> [[WIDE_VEC]], <12 x i32> poison, <4 x i32> <i32 1, i32 4, i32 7, i32 10>
 ; CHECK-NEXT:    [[STRIDED_VEC3:%.*]] = shufflevector <12 x i32> [[WIDE_VEC]], <12 x i32> poison, <4 x i32> <i32 2, i32 5, i32 8, i32 11>
 ; CHECK-NEXT:    [[TMP1:%.*]] = add <4 x i32> [[STRIDED_VEC]], [[VEC_IND]]
-; CHECK-NEXT:    [[TMP2:%.*]] = getelementptr inbounds i32, ptr [[NEXT_GEP]], i64 2
-; CHECK-NEXT:    [[TMP3:%.*]] = add <4 x i32> [[STRIDED_VEC2]], [[VEC_IND]]
-; CHECK-NEXT:    [[TMP4:%.*]] = add <4 x i32> [[STRIDED_VEC3]], [[VEC_IND]]
-; CHECK-NEXT:    [[TMP5:%.*]] = getelementptr inbounds i32, ptr [[TMP2]], i64 -2
-; CHECK-NEXT:    [[TMP6:%.*]] = shufflevector <4 x i32> [[TMP1]], <4 x i32> [[TMP3]], <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7>
-; CHECK-NEXT:    [[TMP7:%.*]] = shufflevector <4 x i32> [[TMP4]], <4 x i32> poison, <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 poison, i32 poison, i32 poison, i32 poison>
-; CHECK-NEXT:    [[INTERLEAVED_VEC:%.*]] = shufflevector <8 x i32> [[TMP6]], <8 x i32> [[TMP7]], <12 x i32> <i32 0, i32 4, i32 8, i32 1, i32 5, i32 9, i32 2, i32 6, i32 10, i32 3, i32 7, i32 11>
-; CHECK-NEXT:    store <12 x i32> [[INTERLEAVED_VEC]], ptr [[TMP5]], align 4
+; CHECK-NEXT:    [[TMP2:%.*]] = add <4 x i32> [[STRIDED_VEC2]], [[VEC_IND]]
+; CHECK-NEXT:    [[TMP3:%.*]] = add <4 x i32> [[STRIDED_VEC3]], [[VEC_IND]]
+; CHECK-NEXT:    [[TMP4:%.*]] = shufflevector <4 x i32> [[TMP1]], <4 x i32> [[TMP2]], <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7>
+; CHECK-NEXT:    [[TMP5:%.*]] = shufflevector <4 x i32> [[TMP3]], <4 x i32> poison, <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 poison, i32 poison, i32 poison, i32 poison>
+; CHECK-NEXT:    [[INTERLEAVED_VEC:%.*]] = shufflevector <8 x i32> [[TMP4]], <8 x i32> [[TMP5]], <12 x i32> <i32 0, i32 4, i32 8, i32 1, i32 5, i32 9, i32 2, i32 6, i32 10, i32 3, i32 7, i32 11>
+; CHECK-NEXT:    store <12 x i32> [[INTERLEAVED_VEC]], ptr [[NEXT_GEP]], align 4
 ; CHECK-NEXT:    [[INDEX_NEXT]] = add nuw i64 [[INDEX]], 4
 ; CHECK-NEXT:    [[VEC_IND_NEXT]] = add <4 x i32> [[VEC_IND]], <i32 4, i32 4, i32 4, i32 4>
-; CHECK-NEXT:    [[TMP8:%.*]] = icmp eq i64 [[INDEX_NEXT]], 1024
-; CHECK-NEXT:    br i1 [[TMP8]], label [[MIDDLE_BLOCK:%.*]], label [[VECTOR_BODY]], !llvm.loop [[LOOP20:![0-9]+]]
+; CHECK-NEXT:    [[TMP6:%.*]] = icmp eq i64 [[INDEX_NEXT]], 1024
+; CHECK-NEXT:    br i1 [[TMP6]], label [[MIDDLE_BLOCK:%.*]], label [[VECTOR_BODY]], !llvm.loop [[LOOP20:![0-9]+]]
 ; CHECK:       middle.block:
 ; CHECK-NEXT:    br i1 true, label [[FOR_COND_CLEANUP:%.*]], label [[SCALAR_PH]]
 ; CHECK:       scalar.ph:
 ; CHECK-NEXT:    br label [[FOR_BODY:%.*]]
 ; CHECK:       for.cond.cleanup:
 ; CHECK-NEXT:    ret void
 ; CHECK:       for.body:
 ; CHECK-NEXT:    br i1 poison, label [[FOR_COND_CLEANUP]], label [[FOR_BODY]], !llvm.loop [[LOOP21:![0-9]+]]