[llvm] [SelectionDAG] Salvage debuginfo when combining load and sext instrs. (PR #169779)

[Matt Arsenault via llvm-commits]

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@@ -0,0 +1,55 @@
+# This test checks that after SelectionDAG runs, it preserves the debug info that is lost due to the DAGCombiner combining a load and a sext instruction, where the #dbg_value is pointing to the result of the load.
+
+# RUN: llc -O2 %s -mtriple=x86_64-unkown-linux -start-before=x86-isel -stop-after=x86-isel -o - | FileCheck %s --check-prefix=MIR
+# RUN: llc -O2 %s -start-before=x86-isel -mtriple=x86_64-unkown-linux --filetype=obj -o %t.o 
+# RUN: llvm-dwarfdump %t.o --name Idx | FileCheck %s --check-prefix=DUMP
+
+# MIR: ![[IDX:[0-9]+]] = !DILocalVariable(name: "Idx"
+# MIR-LABEL: bb.0
+# MIR: %{{[0-9a-f]+}}{{.*}} = MOVSX64rm32 ${{.*}}, 1, $noreg, @GlobArr, $noreg, debug-instr-number [[INSTR_NUM:[0-9]+]]
+# MIR-NEXT: DBG_INSTR_REF ![[IDX]], !DIExpression(DW_OP_LLVM_arg, 0), dbg-instr-ref([[INSTR_NUM]], 0)
+# MIR-NEXT: DBG_INSTR_REF ![[IDX]], !DIExpression(DW_OP_LLVM_arg, 0,  DW_OP_LLVM_convert, 32, DW_ATE_signed, DW_OP_LLVM_convert, 64, DW_ATE_signed), dbg-instr-ref([[INSTR_NUM]], 0)
+
+# DUMP: DW_AT_location	(indexed ({{[0-9a-f]+}}x{{[0-9a-f]+}}) loclist = 0x{{[0-9]+}}: 
+# DUMP-NEXT: [0x{{[0-9a-f]+}}, 0x{{[0-9a-f]+}}): DW_OP_breg0 RAX+0, DW_OP_convert (0x{{[0-9a-f]+}}) "DW_ATE_signed_32", DW_OP_convert (0x{{[0-9a-f]+}}) "DW_ATE_signed_64")
+
+--- |
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arsenm wrote:

Having a SelectionDAG mir test doesn't make any sense 

https://github.com/llvm/llvm-project/pull/169779