[DebugInfo][InstrRef] Fix a broken substitution method, add test coverage

This patch fixes a clearly-broken function that I absent-mindedly bodged
many months ago.

Over in D85749 I landed the substituteDebugValuesForInst, that creates
substitution records for all the def operands from one debug-labelled
instruction to the new one. Unfortunately it would crash if the two
instructions had different numbers of operands; I tried to fix this in
537f0fbe82 by adding a "max operand" parameter to the method, but then
didn't actually change the loop bound to take account of this. It passed
all the tests because.... well there wasn't any real test coverage of this
method.

This patch fixes up the loop to be bounded by the MaxOperand bound; and
adds test coverage for the x86-fixup-LEAs calls to this method, so that
it's actually tested.

Differential Revision: https://reviews.llvm.org/D105820

lib/CodeGen/MachineFunction.cpp

@@ -990,7 +990,7 @@ void MachineFunction::substituteDebugValuesForInst(const MachineInstr &Old,
   // MIR output.
   // Examine all the operands, or the first N specified by the caller.
   MaxOperand = std::min(MaxOperand, Old.getNumOperands());
-  for (unsigned int I = 0; I < Old.getNumOperands(); ++I) {
+  for (unsigned int I = 0; I < MaxOperand; ++I) {
     const auto &OldMO = Old.getOperand(I);
     auto &NewMO = New.getOperand(I);
     (void)NewMO;

test/DebugInfo/MIR/InstrRef/x86-lea-fixup-2.mir

@@ -0,0 +1,62 @@
+# RUN: llc -run-pass x86-fixup-LEAs -mtriple=i386 -verify-machineinstrs -mcpu=corei7-avx -o - %s | FileCheck %s
+#
+# Test that several LEA => ADD transforms get substitutions applied to them,
+# for corner cases that we can only hit with -mtriple=i386.
+---
+name:            test2add_32
+# CHECK: name: test2add_32
+alignment:       16
+tracksRegLiveness: true
+liveins:
+  - { reg: '$eax' }
+  - { reg: '$ebp' }
+# CHECK:       debugValueSubstitutions:
+# CHECK-NAME:  - { srcinst: 1, srcop: 0, dstinst: 2, dstop: 0, subreg: 0 }
+body:             |
+  bb.0:
+    liveins: $eax, $ebp
+
+    ; CHECK: $eax = ADD32ri8 {{.*}} debug-instr-number 2
+    $eax = LEA32r killed $eax, 1, killed $ebp, -5, $noreg, debug-instr-number 1
+    RETQ $eax
+
+...
+---
+name:            test1mov1add_ebp_32
+# CHECK-LABEL: name: test1mov1add_ebp_32
+alignment:       16
+tracksRegLiveness: true
+liveins:
+  - { reg: '$eax' }
+  - { reg: '$ebx' }
+  - { reg: '$ebp' }
+# CHECK:       debugValueSubstitutions:
+# CHECK-NEXT:  - { srcinst: 1, srcop: 0, dstinst: 2, dstop: 0, subreg: 0 }
+body:             |
+  bb.0:
+    liveins: $eax, $ebp, $ebx
+
+    ; CHECK: $ebx = ADD32rr {{.*}} debug-instr-number 2
+    $ebx = LEA32r killed $ebp, 1, $ebp, 0, $noreg, debug-instr-number 1
+    RETQ $ebx
+
+...
+---
+name:            testleaadd_ebp_index_32
+# CHECK-LABEL: name: testleaadd_ebp_index_32
+alignment:       16
+tracksRegLiveness: true
+liveins:
+  - { reg: '$ebx' }
+  - { reg: '$ebp' }
+# CHECK:       debugValueSubstitutions:
+# CHECK-NEXT:  - { srcinst: 1, srcop: 0, dstinst: 2, dstop: 0, subreg: 0 }
+body:             |
+  bb.0:
+    liveins: $eax, $ebp, $ebx
+
+    ; CHECK: $ebx = ADD32rr {{.*}} debug-instr-number 2
+    $ebx = LEA32r $ebp, 1, $ebp, 5, $noreg, debug-instr-number 1
+    RETQ $ebx
+
+...

test/DebugInfo/MIR/InstrRef/x86-lea-fixup.mir

@@ -0,0 +1,77 @@
+# RUN: llc -run-pass x86-fixup-LEAs -mtriple=x86_64-gnu-unknown -verify-machineinstrs -mcpu=corei7-avx -o - %s | FileCheck %s --check-prefix=COREI7
+# RUN: llc -run-pass x86-fixup-LEAs -mtriple=x86_64-gnu-unknown -verify-machineinstrs -mcpu=haswell -o - %s | FileCheck %s --check-prefix=HASWELL
+# RUN: llc -run-pass x86-fixup-LEAs -mtriple=x86_64-unknown-unknown -verify-machineinstrs -mcpu=atom -o - %s | FileCheck %s --check-prefix=ATOM
+#
+# Test several LEA <=> ADD transformations that the fixup-leas pass performs,
+# and check that any debug-instr-number attached to the original instruction
+# is substituted onto the new instruction.
+# Some are only reachable under specific CPU modes it seems -- each function
+# in this file is only tested by one prefix / CPU mode. Some i386 specific
+# behaviours are in the -2 flavour of this file.
+---
+# COREI7-LABE: name: pr43758
+name:            pr43758
+alignment:       16
+tracksRegLiveness: true
+liveins:
+  - { reg: '$rax' }
+  - { reg: '$rbp' }
+# COREI7:      debugValueSubstitutions:
+# COREI7-NEXT: - { srcinst: 1, srcop: 0, dstinst: 2, dstop: 0, subreg: 0 }
+body:             |
+  bb.0:
+    liveins: $rax, $rbp
+
+    $ebp = LEA64_32r killed $rbp, 1, killed $rax, 0, $noreg, debug-instr-number 1
+    ; COREI7: ADD32rr {{.*}} debug-instr-number 2
+    RETQ $ebp
+
+...
+---
+name:            test_mul_spec
+# HASWELL-LABEL: name: test_mul_spec
+alignment:       16
+tracksRegLiveness: true
+liveins:
+  - { reg: '$edi' }
+frameInfo:
+  maxAlignment:    1
+  maxCallFrameSize: 0
+machineFunctionInfo: {}
+# HASWELL:      debugValueSubstitutions:
+# HASWELL-NEXT:  - { srcinst: 1, srcop: 0, dstinst: 3, dstop: 0, subreg: 0 }
+# HASWELL-NEXT:  - { srcinst: 2, srcop: 0, dstinst: 4, dstop: 0, subreg: 0 }
+body:             |
+  bb.0:
+    liveins: $edi
+  
+    renamable $edi = KILL $edi, implicit-def $rdi
+    renamable $ecx = nsw LEA64_32r renamable $rdi, 8, renamable $rdi, 42, $noreg, debug-instr-number 1
+    ; HASWELL: ADD32ri8 {{.*}} debug-instr-number 3
+    renamable $eax = nsw LEA64_32r killed renamable $rdi, 4, renamable $rdi, 2, $noreg, debug-instr-number 2
+    ; HASWELL: ADD32ri8 {{.*}} debug-instr-number 4
+    renamable $eax = nsw IMUL32rr killed renamable $eax, killed renamable $ecx, implicit-def dead $eflags
+    RETQ $eax
+
+...
+---
+name:            testthree
+# ATOM-LABEL: name: testthree
+alignment:       16
+tracksRegLiveness: true
+frameInfo:
+  maxAlignment:    1
+  maxCallFrameSize: 0
+machineFunctionInfo: {}
+# ATOM:       debugValueSubstitutions:
+# ATOM-NEXT:  - { srcinst: 1, srcop: 0, dstinst: 2, dstop: 0, subreg: 0 }
+body:             |
+  bb.0.entry:
+    renamable $ecx = MOV32ri 0
+    renamable $eax = XOR32rr undef $eax, undef $eax, implicit-def dead $eflags
+    renamable $ecx = nsw ADD32rr renamable $ecx, renamable $eax, implicit-def dead $eflags, implicit killed $rax, implicit killed $rcx, implicit-def $rcx, debug-instr-number 1
+    ; ATOM: LEA64_32r {{.*}} debug-instr-number 2
+    renamable $eax = MOV32rm killed renamable $rcx, 1, $noreg, 0, $noreg :: (load (s32) from `i32 *undef`)
+    RETQ $eax
+
+...