AMDGPU: Fix verifier error in SIFoldOperands

[arsenm]

Summary

There may be other use operands that also need their kill flags cleared.

This happens in a few tests when SIFoldOperands is moved after
PeepholeOptimizer.

PeepholeOptimizer rewrites cases that look like:
%vreg0 = ...
%vreg1 = COPY %vreg0
use %vreg1<kill>
%vreg2 = COPY %vreg0
use %vreg2<kill>

to use the earlier source to
%vreg0 = ...
use %vreg0
use %vreg0

Currently SIFoldOperands sees the copied registers, so there is
only one use. So far I haven't managed to come up with a test
that currently has multiple uses of a foldable VGPR -> VGPR copy.

[• tstellarAMD]

LGTM.

[arsenm]

r250960

lib/Target/AMDGPU/SIFoldOperands.cpp

for (I = MBB.begin(); I != MBB.end(); I = Next) {
       for (MachineInstr *Copy : CopiesToReplace)
         Copy->addImplicitDefUseOperands(MF);
 
       for (FoldCandidate &Fold : FoldList) {
         if (updateOperand(Fold, TRI)) {
           // Clear kill flags.
           if (!Fold.isImm()) {
             assert(Fold.OpToFold && Fold.OpToFold->isReg());
-            Fold.OpToFold->setIsKill(false);
+            // FIXME: Probably shouldn't bother trying to fold if not an
+            // SGPR. PeepholeOptimizer can eliminate redundant VGPR->VGPR
+            // copies.
+            MRI.clearKillFlags(Fold.OpToFold->getReg());
           }
           DEBUG(dbgs() << "Folded source from " << MI << " into OpNo " <<
                 Fold.UseOpNo << " of " << *Fold.UseMI << '\n');
         }
       }
     }
   }
   return false;
 }

test/CodeGen/AMDGPU/si-instr-info-correct-implicit-operands.ll

 ; RUN: llc -o /dev/null %s -march=amdgcn -mcpu=verde -verify-machineinstrs -stop-after expand-isel-pseudos 2>&1 | FileCheck %s
 ; This test verifies that the instruction selection will add the implicit
 ; register operands in the correct order when modifying the opcode of an
 ; instruction to V_ADD_I32_e32.
 
-; CHECK: %19 = V_ADD_I32_e32 killed %13, killed %12, implicit-def %vcc, implicit %exec
+; CHECK: %19 = V_ADD_I32_e32 %13, %12, implicit-def %vcc, implicit %exec
 
 define void @test(i32 addrspace(1)* %out, i32 addrspace(1)* %in) {
 entry:
   %b_ptr = getelementptr i32, i32 addrspace(1)* %in, i32 1
   %a = load i32, i32 addrspace(1)* %in
   %b = load i32, i32 addrspace(1)* %b_ptr
   %result = add i32 %a, %b
   store i32 %result, i32 addrspace(1)* %out
   ret void
 }