GlobalISel: Fix IRTranslator for constantexpr selects

[arsenm]

Summary

This was assuming a select is always an instruction, which is not
true.

[foad]

Seems obvious.

[arsenm]

a7759d178508771a5ccec2b02ca3f3bd40af4409

llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp

 
 bool IRTranslator::translateSelect(const User &U,
                                    MachineIRBuilder &MIRBuilder) {
   Register Tst = getOrCreateVReg(*U.getOperand(0));
   ArrayRef<Register> ResRegs = getOrCreateVRegs(U);
   ArrayRef<Register> Op0Regs = getOrCreateVRegs(*U.getOperand(1));
   ArrayRef<Register> Op1Regs = getOrCreateVRegs(*U.getOperand(2));
 
-  const SelectInst &SI = cast<SelectInst>(U);
   uint16_t Flags = 0;
-  if (const CmpInst *Cmp = dyn_cast<CmpInst>(SI.getCondition()))
+  if (const SelectInst *SI = dyn_cast<SelectInst>(&U)) {
+    if (const CmpInst *Cmp = dyn_cast<CmpInst>(SI->getCondition()))
       Flags = MachineInstr::copyFlagsFromInstruction(*Cmp);
+  }
 
   for (unsigned i = 0; i < ResRegs.size(); ++i) {
     MIRBuilder.buildSelect(ResRegs[i], Tst, Op0Regs[i], Op1Regs[i], Flags);
   }
 
   return true;
 }
 

llvm/test/CodeGen/AMDGPU/GlobalISel/irtranslator-constantexpr.ll

+; NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
+; RUN: llc -global-isel -mtriple=amdgcn-amd-amdhsa -mcpu=gfx900 -stop-after=irtranslator -o - %s | FileCheck %s
+
+@gint = external addrspace(1) global i8, align 4
+
+; Technically we should be able to fold away the compare to true, but
+; currently constexpr doesn't understand null in non-0 address spaces.
+define amdgpu_kernel void @constantexpr_select_0() {
+  ; CHECK-LABEL: name: constantexpr_select_0
+  ; CHECK: bb.1 (%ir-block.0):
+  ; CHECK:   [[GV:%[0-9]+]]:_(p1) = G_GLOBAL_VALUE @gint
+  ; CHECK:   [[C:%[0-9]+]]:_(p1) = G_CONSTANT i64 0
+  ; CHECK:   [[ICMP:%[0-9]+]]:_(s1) = G_ICMP intpred(eq), [[GV]](p1), [[C]]
+  ; CHECK:   [[C1:%[0-9]+]]:_(s32) = G_CONSTANT i32 1
+  ; CHECK:   [[C2:%[0-9]+]]:_(s32) = G_CONSTANT i32 0
+  ; CHECK:   [[SELECT:%[0-9]+]]:_(s32) = G_SELECT [[ICMP]](s1), [[C1]], [[C2]]
+  ; CHECK:   [[DEF:%[0-9]+]]:_(p1) = G_IMPLICIT_DEF
+  ; CHECK:   G_STORE [[SELECT]](s32), [[DEF]](p1) :: (store 4 into `i32 addrspace(1)* undef`, addrspace 1)
+  ; CHECK:   S_ENDPGM 0
+  store i32 select (i1 icmp eq (i8 addrspace(1)* @gint, i8 addrspace(1)* null), i32 1, i32 0), i32 addrspace(1)* undef, align 4
+  ret void
+}
+
+define amdgpu_kernel void @constantexpr_select_1() {
+  ; CHECK-LABEL: name: constantexpr_select_1
+  ; CHECK: bb.1 (%ir-block.0):
+  ; CHECK:   [[C:%[0-9]+]]:_(s64) = G_CONSTANT i64 1024
+  ; CHECK:   [[INTTOPTR:%[0-9]+]]:_(p1) = G_INTTOPTR [[C]](s64)
+  ; CHECK:   [[GV:%[0-9]+]]:_(p1) = G_GLOBAL_VALUE @gint
+  ; CHECK:   [[ICMP:%[0-9]+]]:_(s1) = G_ICMP intpred(eq), [[INTTOPTR]](p1), [[GV]]
+  ; CHECK:   [[C1:%[0-9]+]]:_(s32) = G_CONSTANT i32 1
+  ; CHECK:   [[C2:%[0-9]+]]:_(s32) = G_CONSTANT i32 0
+  ; CHECK:   [[SELECT:%[0-9]+]]:_(s32) = G_SELECT [[ICMP]](s1), [[C1]], [[C2]]
+  ; CHECK:   [[DEF:%[0-9]+]]:_(p1) = G_IMPLICIT_DEF
+  ; CHECK:   G_STORE [[SELECT]](s32), [[DEF]](p1) :: (store 4 into `i32 addrspace(1)* undef`, addrspace 1)
+  ; CHECK:   S_ENDPGM 0
+  store i32 select (i1 icmp eq (i8 addrspace(1)* @gint, i8 addrspace(1)* inttoptr (i64 1024 to i8 addrspace(1)*)), i32 1, i32 0), i32 addrspace(1)* undef, align 4
+  ret void
+}