[Statepoints] FixupStatepoint: Clear isKill flag if COPY is not deleted.

[dantrushin]

Summary

When spilling CSRs, FixupStatepoint pass does simple copy propagation,
trying to find COPY instruction which defines register being spilled
and spill COPY source instead. I.e., if we have CSR $x and found

$x = COPY $y

we will spill $y instead.
But we may be unable to delete COPY instruction for some reason.
Then, spill will be inserted after it, adding another use of $y.
If COPY instruction was last use of $y (killed it), after insertion of
the spill it is not, so isKill flag must be cleared. We failed to do
so and this patch fixes this issue.

[skatkov]

Can you please land the test first and in this patch upload the diff what changed.

[dantrushin]

Rebase on top of precommitted test

[dantrushin]

Fix spaces in test to minimize differences

[skatkov]

Thanks!

llvm/lib/CodeGen/FixupStatepointCallerSaved.cpp

static Register performCopyPropagation(Register Reg,
   LLVM_DEBUG(dbgs() << "spillRegisters: perform copy propagation "
                     << printReg(Reg, &TRI) << " -> " << printReg(SrcReg, &TRI)
                     << "\n");
 
   // Insert spill immediately after Def
   RI = ++MachineBasicBlock::iterator(Def);
   IsKill = DestSrc->Source->isKill();
 
+  if (!Use) {
     // There are no uses of original register between COPY and STATEPOINT.
     // There can't be any after STATEPOINT, so we can eliminate Def.
-  if (!Use) {
     LLVM_DEBUG(dbgs() << "spillRegisters: removing dead copy " << *Def);
     Def->eraseFromParent();
+  } else if (IsKill) {
+    // COPY will remain in place, spill will be inserted *after* it, so it is
+    // not a kill of source anymore.
+    const_cast<MachineOperand *>(DestSrc->Source)->setIsKill(false);
   }
+
   return SrcReg;
 }
 
 namespace {
 // Pair {Register, FrameIndex}
 using RegSlotPair = std::pair<Register, int>;
 
 // Keeps track of what reloads were inserted in MBB.

llvm/test/CodeGen/X86/statepoint-fixup-copy-prop.mir

-# RUN: not --crash llc -o - %s -run-pass fixup-statepoint-caller-saved -verify-machineinstrs 2>&1 | FileCheck %s
+# RUN: llc -o - %s -run-pass fixup-statepoint-caller-saved -verify-machineinstrs | FileCheck %s
 
 --- |
   target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
   target triple = "x86_64-pc-linux-gnu"
 
   declare void @foo(i64)
 
   define i8 addrspace(1)* @test_cp(i64 %a, i64 %b, i64 %c, i8 addrspace(1)* %p) gc "statepoint-example" {
     ret i8 addrspace(1)* undef
   }
 ...
 ---
 name:            test_cp
 alignment:       16
 tracksRegLiveness: true
 liveins:
   - { reg: '$rdi', virtual-reg: '' }
 frameInfo:
 body:             |
   bb.0:
     liveins: $rax, $rdi, $rbp
 
-
-    ; CHECK: # After Fixup Statepoint Caller Saved
-    ; CHECK: # Machine code for function test_cp:
-    ; CHECK:   bb.0:
-    ; CHECK:     liveins: $rax, $rdi, $rbp
-    ; CHECK:   renamable $rdi = COPY killed renamable $rax
+    ; CHECK:   renamable $rdi = COPY renamable $rax
     ; CHECK:   MOV64mr %stack.1, 1, $noreg, 0, $noreg, killed $rax :: (store (s64) into %stack.1)
     ; CHECK:   renamable $rax = MOV64rm renamable $rdi, 1, $noreg, 16, $noreg
     ; CHECK:   MOV64mr %stack.0, 1, $noreg, 0, $noreg, killed $rax :: (store (s64) into %stack.0)
-    ; CHECK:   STATEPOINT 0, 0, 0, @foo, 2, 0, 2, 0, 2, 1, 1, 8, %stack.0, 0, 2, 1, 1, 8, %stack.1, 0, 2, 0, 2, 1, 0, 0, <regmask $bh $bl $bp $bph $bpl $bx $ebp $ebx $hbp $hbx $rbp $rbx $r12 $r13 $r14 $r15 $r12b $r13b $r14b $r15b $r12bh $r13bh $r14bh $r15bh $r12d $r13d $r14d $r15d $r12w $r13w $r14w $r15w $r12wh and 3 more...>, implicit-def $rsp, implicit-def $ssp
-    ; CHECK: *** Bad machine code: Using an undefined physical register ***
-    ; CHECK: - function:    test_cp
-    ; CHECK: - basic block: %bb.0
-    ; CHECK: - instruction: MOV64mr %stack.1, 1, $noreg, 0, $noreg, killed $rax :: (store (s64) into %stack.1)
-    ; CHECK: - operand 5:   killed $rax
-    ; CHECK: LLVM ERROR: Found 1 machine code errors.
+    ; CHECK:   STATEPOINT 0, 0, 0, @foo, 2, 0, 2, 0, 2, 1, 1, 8, %stack.0, 0, 2, 1, 1, 8, %stack.1, 0, 2, 0, 2, 1, 0, 0, csr_64, implicit-def $rsp, implicit-def $ssp :: (load (s64) from %stack.0), (load store (s64) on %stack.1)
     renamable $rdi = COPY killed renamable $rax
     renamable $rax = MOV64rm renamable $rdi, 1, $noreg, 16, $noreg
     renamable $rdi = STATEPOINT 0, 0, 0, @foo, 2, 0, 2, 0, 2, 1, renamable $rax, 2, 1, killed renamable $rdi(tied-def 0), 2, 0, 2, 1, 0, 0, csr_64, implicit-def $rsp, implicit-def $ssp
     $rax = COPY killed renamable $rdi
     RET 0, killed $rax
 ...