AMDGPU: Don't add same instruction multiple times to worklist

[arsenm]

Summary

When the instruction is processed the first time, it may be
deleted resulting in crashes. While the new test adds the same
user to the worklist twice, this particular case doesn't crash
but I'm not sure why.

[• tstellarAMD]

LGTM.

[arsenm]

r290191

lib/Target/AMDGPU/SIInstrInfo.cpp

void SIInstrInfo::splitScalar64BitBFE(SmallVectorImpl<MachineInstr *> &Worklist,
   addUsersToMoveToVALUWorklist(ResultReg, MRI, Worklist);
 }
 
 void SIInstrInfo::addUsersToMoveToVALUWorklist(
   unsigned DstReg,
   MachineRegisterInfo &MRI,
   SmallVectorImpl<MachineInstr *> &Worklist) const {
   for (MachineRegisterInfo::use_iterator I = MRI.use_begin(DstReg),
-         E = MRI.use_end(); I != E; ++I) {
+         E = MRI.use_end(); I != E;) {
     MachineInstr &UseMI = *I->getParent();
     if (!canReadVGPR(UseMI, I.getOperandNo())) {
       Worklist.push_back(&UseMI);
+
+      do {
+        ++I;
+      } while (I != E && I->getParent() == &UseMI);
+    } else {
+      ++I;
     }
   }
 }
 
 void SIInstrInfo::addSCCDefUsersToVALUWorklist(
     MachineInstr &SCCDefInst, SmallVectorImpl<MachineInstr *> &Worklist) const {
   // This assumes that all the users of SCC are in the same block
   // as the SCC def.

test/CodeGen/AMDGPU/sminmax.ll

define void @v_abs_i32(i32 addrspace(1)* %out, i32 addrspace(1)* %src) nounwind {
   %neg = sub i32 0, %val
   %cond = icmp sgt i32 %val, %neg
   %res = select i1 %cond, i32 %val, i32 %neg
   %res2 = add i32 %res, 2
   store i32 %res2, i32 addrspace(1)* %out, align 4
   ret void
 }
 
+; GCN-LABEL: {{^}}v_abs_i32_repeat_user:
+; GCN: v_sub_i32_e32 [[NEG:v[0-9]+]], vcc, 0, [[SRC:v[0-9]+]]
+; GCN: v_max_i32_e32 [[MAX:v[0-9]+]], [[NEG]], [[SRC]]
+; GCN: v_mul_lo_i32 v{{[0-9]+}}, [[MAX]], [[MAX]]
+define void @v_abs_i32_repeat_user(i32 addrspace(1)* %out, i32 addrspace(1)* %src) nounwind {
+  %val = load i32, i32 addrspace(1)* %src, align 4
+  %neg = sub i32 0, %val
+  %cond = icmp sgt i32 %val, %neg
+  %res = select i1 %cond, i32 %val, i32 %neg
+  %mul = mul i32 %res, %res
+  store i32 %mul, i32 addrspace(1)* %out, align 4
+  ret void
+}
+
 ; FUNC-LABEL: {{^}}s_abs_v2i32:
 ; GCN: s_abs_i32
 ; GCN: s_abs_i32
 ; GCN: s_add_i32
 ; GCN: s_add_i32
 
 ; EG: MAX_INT
 ; EG: MAX_INT