[LoopInterchange] Fix crash when dbg_value exists right after PHI (llvm#208147)

When enabling reduction2mem with `-loop-interchange-reduction-to-mem`
and the input IR contains `dbg_value`s immediately after a certain PHI
node, assertion failure could be triggered due to the insertion position
of newly created PHI node. This patch fixes the issue by changing
IRBuilder ctor to be called. TBH, I'm not entirely sure what the
difference is between `IRBuilder::IRBuilder(Instruction *)` and
`IRBuilder::IRBuilder(BasicBlock *, BasicBlock::iterator)`, but judging
from the generated code, the behavior with this patch seems reasonable.

Taken over from llvm#183273

Author: kasuga-fj

llvm/lib/Transforms/Scalar/LoopInterchange.cpp

@@ -2074,7 +2074,7 @@ void LoopInterchangeTransform::reduction2Memory() {
 
   LoopInterchangeLegality::InnerReduction SR = InnerReductions[0];
   BasicBlock *InnerLoopHeader = InnerLoop->getHeader();
-  IRBuilder<> Builder(&*(InnerLoopHeader->getFirstNonPHIIt()));
+  IRBuilder<> Builder(InnerLoopHeader, InnerLoopHeader->getFirstNonPHIIt());
 
   // Check if it's the first iteration.
   LLVMContext &Context = InnerLoopHeader->getContext();

llvm/test/Transforms/LoopInterchange/debug-record-after-phi.ll

@@ -0,0 +1,96 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 6
+; RUN: opt < %s -passes=loop-interchange -loop-interchange-profitabilities=ignore -loop-interchange-reduction-to-mem -S | FileCheck %s
+
+define void @f(ptr %A) {
+; CHECK-LABEL: define void @f(
+; CHECK-SAME: ptr [[A:%.*]]) {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    br label %[[FOR_J_PREHEADER:.*]]
+; CHECK:       [[FOR_I_HEADER_PREHEADER:.*]]:
+; CHECK-NEXT:    br label %[[FOR_I_HEADER:.*]]
+; CHECK:       [[FOR_I_HEADER]]:
+; CHECK-NEXT:    [[I:%.*]] = phi i64 [ [[I_NEXT:%.*]], %[[FOR_I_LATCH:.*]] ], [ 0, %[[FOR_I_HEADER_PREHEADER]] ]
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr double, ptr [[A]], i64 [[I]]
+; CHECK-NEXT:    br label %[[FOR_J_SPLIT1:.*]]
+; CHECK:       [[FOR_J_PREHEADER]]:
+; CHECK-NEXT:    br label %[[FOR_J:.*]]
+; CHECK:       [[FOR_J]]:
+; CHECK-NEXT:    [[J:%.*]] = phi i64 [ [[TMP1:%.*]], %[[FOR_J_SPLIT:.*]] ], [ 0, %[[FOR_J_PREHEADER]] ]
+; CHECK-NEXT:    [[RED:%.*]] = phi double [ [[RED_NEXT_LCSSA2:%.*]], %[[FOR_J_SPLIT]] ], [ 0.000000e+00, %[[FOR_J_PREHEADER]] ]
+; CHECK-NEXT:    [[FIRST_ITER:%.*]] = phi i1 [ false, %[[FOR_J_SPLIT]] ], [ true, %[[FOR_J_PREHEADER]] ]
+; CHECK-NEXT:    br label %[[FOR_I_HEADER_PREHEADER]]
+; CHECK:       [[FOR_J_SPLIT1]]:
+; CHECK-NEXT:    [[TMP0:%.*]] = load double, ptr [[GEP]], align 8
+; CHECK-NEXT:    [[NEW_VAR:%.*]] = select i1 [[FIRST_ITER]], double 0.000000e+00, double [[TMP0]]
+; CHECK-NEXT:      #dbg_value(i64 [[J]], [[META3:![0-9]+]], !DIExpression(), [[META10:![0-9]+]])
+; CHECK-NEXT:    [[J_NEXT:%.*]] = add i64 [[J]], 1
+; CHECK-NEXT:    [[RED_NEXT:%.*]] = fadd reassoc double 1.000000e+00, [[NEW_VAR]]
+; CHECK-NEXT:    store double [[RED_NEXT]], ptr [[GEP]], align 8
+; CHECK-NEXT:    [[EC_J:%.*]] = icmp eq i64 [[J_NEXT]], 10
+; CHECK-NEXT:    br label %[[FOR_I_LATCH]]
+; CHECK:       [[FOR_J_SPLIT]]:
+; CHECK-NEXT:    [[RED_NEXT_LCSSA2]] = phi double [ [[RED_NEXT]], %[[FOR_I_LATCH]] ]
+; CHECK-NEXT:    [[RED_NEXT_LCSSA:%.*]] = phi double [ [[RED_NEXT]], %[[FOR_I_LATCH]] ]
+; CHECK-NEXT:    [[TMP1]] = add i64 [[J]], 1
+; CHECK-NEXT:    [[TMP2:%.*]] = icmp eq i64 [[TMP1]], 10
+; CHECK-NEXT:    br i1 [[TMP2]], label %[[EXIT:.*]], label %[[FOR_J]]
+; CHECK:       [[FOR_I_LATCH]]:
+; CHECK-NEXT:    [[I_NEXT]] = add i64 [[I]], 1
+; CHECK-NEXT:    [[EC_I:%.*]] = icmp eq i64 [[I_NEXT]], 10
+; CHECK-NEXT:    br i1 [[EC_I]], label %[[FOR_J_SPLIT]], label %[[FOR_I_HEADER]]
+; CHECK:       [[EXIT]]:
+; CHECK-NEXT:    ret void
+;
+entry:
+  br label %for.i.header
+
+for.i.header:
+  %i = phi i64 [ 0, %entry ], [ %i.next, %for.i.latch ]
+  %gep = getelementptr double, ptr %A, i64 %i
+  br label %for.j
+
+for.j:
+  %j = phi i64 [ 0, %for.i.header ], [ %j.next, %for.j ]
+  %red = phi double [ 0.000000e+00, %for.i.header ], [ %red.next, %for.j ]
+    #dbg_value(i64 %j, !3, !DIExpression(), !13)
+  %j.next = add i64 %j, 1
+  %red.next = fadd reassoc double 1.000000e+00, %red
+  %ec.j = icmp eq i64 %j.next, 10
+  br i1 %ec.j, label %for.i.latch, label %for.j
+
+for.i.latch:
+  store double %red.next, ptr %gep
+  %i.next = add i64 %i, 1
+  %ec.i = icmp eq i64 %i.next, 10
+  br i1 %ec.i, label %exit, label %for.i.header
+
+exit:
+  ret void
+}
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!2}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C11, file: !1, isOptimized: false, runtimeVersion: 0, emissionKind: NoDebug)
+!1 = !DIFile(filename: "test.c", directory: "/home/abc/wyy/test/FirstIter_DbgRecords", checksumkind: CSK_MD5, checksum: "69b1c47396b37bc8b48d5517efe4fb54")
+!2 = !{i32 2, !"Debug Info Version", i32 3}
+!3 = !DILocalVariable(name: "j", scope: !4, file: !1, line: 7, type: !12)
+!4 = distinct !DILexicalBlock(scope: !8, file: !1, line: 7, column: 5)
+!8 = distinct !DISubprogram(name: "func", scope: !1, file: !1, line: 2, type: !9, scopeLine: 2, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !11, keyInstructions: true)
+!9 = !DISubroutineType(types: !10)
+!10 = !{null}
+!11 = !{}
+!12 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!13 = !DILocation(line: 0, scope: !4)
+;.
+; CHECK: [[META0:![0-9]+]] = distinct !DICompileUnit(language: DW_LANG_C11, file: [[META1:![0-9]+]], isOptimized: false, runtimeVersion: 0, emissionKind: NoDebug)
+; CHECK: [[META1]] = !DIFile(filename: "{{.*}}test.c", directory: {{.*}}, checksumkind: CSK_MD5, checksum: "69b1c47396b37bc8b48d5517efe4fb54")
+; CHECK: [[META3]] = !DILocalVariable(name: "j", scope: [[META4:![0-9]+]], file: [[META1]], line: 7, type: [[META9:![0-9]+]])
+; CHECK: [[META4]] = distinct !DILexicalBlock(scope: [[META5:![0-9]+]], file: [[META1]], line: 7, column: 5)
+; CHECK: [[META5]] = distinct !DISubprogram(name: "func", scope: [[META1]], file: [[META1]], line: 2, type: [[META6:![0-9]+]], scopeLine: 2, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: [[META0]], retainedNodes: [[META8:![0-9]+]], keyInstructions: true)
+; CHECK: [[META6]] = !DISubroutineType(types: [[META7:![0-9]+]])
+; CHECK: [[META7]] = !{null}
+; CHECK: [[META8]] = !{}
+; CHECK: [[META9]] = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+; CHECK: [[META10]] = !DILocation(line: 0, scope: [[META4]])
+;.