[IRSim] Ignore debug instructions when creating canonical numbering

When constructing canonical relationships between two regions, the first instruction of a basic block from the first region is used to find the corresponding basic block from the second region. However, debug instructions are not included in similarity matching, and therefore do not have a canonical numbering. This patch makes sure to ignore the debug instructions when finding the first instruction in a basic block.

Reviewer: paquette

Differential Revision: https://reviews.llvm.org/D123903

Author: AndrewLitteken

llvm/lib/Analysis/IRSimilarityIdentifier.cpp

@@ -1039,8 +1039,9 @@ void IRSimilarityCandidate::createCanonicalRelationFrom(
     // If the basic block is the starting block, then the shared instruction may
     // not be the first instruction in the block, it will be the first
     // instruction in the similarity region.
-    Value *FirstOutlineInst =
-        BB == getStartBB() ? frontInstruction() : &BB->front();
+    Value *FirstOutlineInst = BB == getStartBB()
+                                  ? frontInstruction()
+                                  : &*BB->instructionsWithoutDebug().begin();
 
     unsigned FirstInstGVN = *getGVN(FirstOutlineInst);
     unsigned FirstInstCanonNum = *getCanonicalNum(FirstInstGVN);

llvm/test/Analysis/IRSimilarityIdentifier/debug-inst-starts-block.ll

@@ -0,0 +1,74 @@
+; RUN: opt -disable-output -S -passes=print-ir-similarity < %s 2>&1 | FileCheck %s
+
+; When a debug instruction is the first instruction in a block, when that block
+; has not been given a canonical numbering, since debug instructions are not
+; counted in similarity matching they must be ignored when creating canonical
+; relations from one region to another.  This checks that this is enforced.
+
+; CHECK: 2 candidates of length 3.  Found in: 
+; CHECK-NEXT:   Function: main, Basic Block: entry
+; CHECK-NEXT:     Start Instruction:   br label %for.body169
+; CHECK-NEXT:       End Instruction:   %1 = sub i32 1, 4
+; CHECK-NEXT:   Function: main, Basic Block: for.body169
+; CHECK-NEXT:     Start Instruction:   br label %for.end122
+; CHECK-NEXT:       End Instruction:   %3 = sub i32 1, 4
+; CHECK-NEXT: 2 candidates of length 2.  Found in: 
+; CHECK-NEXT:   Function: main, Basic Block: for.end122
+; CHECK-NEXT:     Start Instruction:   store i32 30, ptr undef, align 1
+; CHECK-NEXT:       End Instruction:   %1 = sub i32 1, 4
+; CHECK-NEXT:   Function: main, Basic Block: for.end246
+; CHECK-NEXT:     Start Instruction:   store i32 0, ptr undef, align 1
+; CHECK-NEXT:       End Instruction:   %3 = sub i32 1, 4
+; CHECK-NEXT: 2 candidates of length 4.  Found in: 
+; CHECK-NEXT:   Function: main, Basic Block: entry
+; CHECK-NEXT:     Start Instruction:   %0 = add i32 1, 4
+; CHECK-NEXT:       End Instruction:   %1 = sub i32 1, 4
+; CHECK-NEXT:   Function: main, Basic Block: for.body169
+; CHECK-NEXT:     Start Instruction:   %2 = add i32 1, 4
+; CHECK-NEXT:       End Instruction:   %3 = sub i32 1, 4
+
+source_filename = "irsimilarity_crash.ll"
+
+@v_13 = external dso_local global ptr, align 1
+
+; Function Attrs: nocallback nofree nosync nounwind readnone speculatable willreturn
+declare void @llvm.dbg.declare(metadata, metadata, metadata) #0
+
+define dso_local i16 @main() {
+entry:
+  %0 = add i32 1, 4
+  br label %for.body169
+
+for.end122:                                       ; preds = %for.cond108
+  store i32 30, ptr undef, align 1
+  %1 = sub i32 1, 4
+  ret i16 1
+
+for.body169:                                      ; preds = %for.cond167
+  %2 = add i32 1, 4
+  br label %for.end122
+
+for.end246:                                     ; preds = %for.cond167
+  call void @llvm.dbg.declare(metadata ptr undef, metadata !1, metadata !DIExpression()), !dbg !11
+  store i32 0, ptr undef, align 1
+  %3 = sub i32 1, 4
+  unreachable
+}
+
+attributes #0 = { nocallback nofree nosync nounwind readnone speculatable willreturn }
+
+!llvm.dbg.cu = !{}
+!llvm.module.flags = !{!0}
+
+!0 = !{i32 2, !"Debug Info Version", i32 3}
+!1 = !DILocalVariable(name: "v_68", scope: !2, file: !3, line: 522, type: !10)
+!2 = distinct !DILexicalBlock(scope: !4, file: !3, line: 522, column: 9)
+!3 = !DIFile(filename: "41097217.c", directory: "rt.outdir")
+!4 = distinct !DISubprogram(name: "main", scope: !3, file: !3, line: 480, type: !5, scopeLine: 481, spFlags: DISPFlagDefinition, unit: !8, retainedNodes: !9)
+!5 = !DISubroutineType(types: !6)
+!6 = !{!7}
+!7 = !DIBasicType(name: "int", size: 16, encoding: DW_ATE_signed)
+!8 = distinct !DICompileUnit(language: DW_LANG_C99, file: !3, producer: "clang version 15.0.0.prerel", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, retainedTypes: !9, globals: !9, splitDebugInlining: false, nameTableKind: None)
+!9 = !{}
+!10 = !DIBasicType(name: "long", size: 32, encoding: DW_ATE_signed)
+!11 = !DILocation(line: 522, column: 23, scope: !2)