[GlobalISel] Always direct-call IFuncs and Aliases (llvm#74902)

This is safe because for both cases, the use must be in the same TU as the definition, and they cannot be forward declared.

Author: jroelofs

llvm/lib/CodeGen/GlobalISel/CallLowering.cpp

@@ -144,7 +144,12 @@ bool CallLowering::lowerCall(MachineIRBuilder &MIRBuilder, const CallBase &CB,
   const Value *CalleeV = CB.getCalledOperand()->stripPointerCasts();
   if (const Function *F = dyn_cast<Function>(CalleeV))
     Info.Callee = MachineOperand::CreateGA(F, 0);
-  else
+  else if (isa<GlobalIFunc>(CalleeV) || isa<GlobalAlias>(CalleeV)) {
+    // IR IFuncs and Aliases can't be forward declared (only defined), so the
+    // callee must be in the same TU and therefore we can direct-call it without
+    // worrying about it being out of range.
+    Info.Callee = MachineOperand::CreateGA(cast<GlobalValue>(CalleeV), 0);
+  } else
     Info.Callee = MachineOperand::CreateReg(GetCalleeReg(), false);
 
   Register ReturnHintAlignReg;

llvm/test/CodeGen/AArch64/GlobalISel/call-lowering-alias.ll

@@ -0,0 +1,27 @@
+; NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
+; RUN: llc -mtriple=aarch64-elf -global-isel -stop-after=irtranslator -verify-machineinstrs -o - %s | FileCheck %s
+
+@foo_alias = alias ptr, ptr @callee
+
+define internal ptr @callee() {
+  ; CHECK-LABEL: name: callee
+  ; CHECK: bb.1.entry:
+  ; CHECK-NEXT:   [[C:%[0-9]+]]:_(p0) = G_CONSTANT i64 0
+  ; CHECK-NEXT:   $x0 = COPY [[C]](p0)
+  ; CHECK-NEXT:   RET_ReallyLR implicit $x0
+entry:
+  ret ptr null
+}
+
+define void @caller() {
+  ; CHECK-LABEL: name: caller
+  ; CHECK: bb.1.entry:
+  ; CHECK-NEXT:   ADJCALLSTACKDOWN 0, 0, implicit-def $sp, implicit $sp
+  ; CHECK-NEXT:   BL @foo_alias, csr_aarch64_aapcs, implicit-def $lr, implicit $sp, implicit-def $w0
+  ; CHECK-NEXT:   ADJCALLSTACKUP 0, 0, implicit-def $sp, implicit $sp
+  ; CHECK-NEXT:   [[COPY:%[0-9]+]]:_(s32) = COPY $w0
+  ; CHECK-NEXT:   RET_ReallyLR
+entry:
+  %0 = call i32 @foo_alias()
+  ret void
+}

llvm/test/CodeGen/AArch64/GlobalISel/call-lowering-ifunc.ll

@@ -0,0 +1,28 @@
+; NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
+; RUN: llc -mtriple=aarch64-macho -global-isel -stop-after=irtranslator -verify-machineinstrs -o - %s | FileCheck %s
+; RUN: llc -mtriple=aarch64-elf -global-isel -stop-after=irtranslator -verify-machineinstrs -o - %s | FileCheck %s
+
+@foo_ifunc = ifunc i32 (i32), ptr @foo_resolver
+
+define internal ptr @foo_resolver() {
+  ; CHECK-LABEL: name: foo_resolver
+  ; CHECK: bb.1.entry:
+  ; CHECK-NEXT:   [[C:%[0-9]+]]:_(p0) = G_CONSTANT i64 0
+  ; CHECK-NEXT:   $x0 = COPY [[C]](p0)
+  ; CHECK-NEXT:   RET_ReallyLR implicit $x0
+entry:
+  ret ptr null
+}
+
+define void @caller() {
+  ; CHECK-LABEL: name: caller
+  ; CHECK: bb.1.entry:
+  ; CHECK-NEXT:   ADJCALLSTACKDOWN 0, 0, implicit-def $sp, implicit $sp
+  ; CHECK-NEXT:   BL @foo_ifunc, csr_aarch64_aapcs, implicit-def $lr, implicit $sp, implicit-def $w0
+  ; CHECK-NEXT:   ADJCALLSTACKUP 0, 0, implicit-def $sp, implicit $sp
+  ; CHECK-NEXT:   [[COPY:%[0-9]+]]:_(s32) = COPY $w0
+  ; CHECK-NEXT:   RET_ReallyLR
+entry:
+  %0 = call i32 @foo_ifunc()
+  ret void
+}