[llvm] [InstrRef] Preserve debug instr num in aarch64-ldst-opt. (PR #136009)

[Shubham Sandeep Rastogi via llvm-commits]

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@@ -1227,6 +1249,79 @@ AArch64LoadStoreOpt::mergePairedInsns(MachineBasicBlock::iterator I,
             .addImm(0)
             .addImm(31);
     (void)MIBSXTW;
+
+    // In the case of a sign-extend, where we have something like:
+    // debugValueSubstitutions:[]
+    // $w1 = LDRWui $x0, 1, debug-instr-number 1
+    // DBG_INSTR_REF !7, dbg-instr-ref(1, 0), debug-location !9
+    // $x0 = LDRSWui $x0, 0, debug-instr-number 2
+    // DBG_INSTR_REF !8, dbg-instr-ref(2, 0), debug-location !9
+
+    // It will be converted to:
+    // debugValueSubstitutions:[]
+    // $w0, $w1 = LDPWi $x0, 0
+    // $w0 = KILL $w0, implicit-def $x0
+    // $x0 = SBFMXri $x0, 0, 31
+    // DBG_INSTR_REF !7, dbg-instr-ref(1, 0), debug-location !9
+    // DBG_INSTR_REF !8, dbg-instr-ref(2, 0), debug-location !9
+
+    // $x0 is where the final value is stored, so the sign extend (SBFMXri)
+    // instruction contains the final value we care about we give it a new
+    // debug-instr-number 3. Whereas, $w1 contains the final value that we care
+    // about, therefore the LDP instruction is also given a new
+    // debug-instr-number 4. We have to add these subsitutions to the
+    // debugValueSubstitutions table. However, we also have to ensure that the
+    // OpIndex that pointed to debug-instr-number 1 gets updated to 1, because
+    // $w1 is the second operand of the LDP instruction.
+
+    // We want the final result to look like:
+    // debugValueSubstitutions:
+    // - { srcinst: 1, srcop: 0, dstinst: 4, dstop: 1, subreg: 0 }
+    // - { srcinst: 2, srcop: 0, dstinst: 3, dstop: 0, subreg: 0 }
+    // $w0, $w1 = LDPWi $x0, 0, debug-instr-number 4
+    // $w0 = KILL $w0, implicit-def $x0
+    // $x0 = SBFMXri $x0, 0, 31, debug-instr-number 3
+    // DBG_INSTR_REF !7, dbg-instr-ref(1, 0), debug-location !9
+    // DBG_INSTR_REF !8, dbg-instr-ref(2, 0), debug-location !9
----------------
rastogishubham wrote:

I think that sounds good

https://github.com/llvm/llvm-project/pull/136009