[TargetMachine] Don't imply dso_local on global variable declarations in Reloc::Static model

clang/lib/CodeGen/CodeGenModule sets dso_local on applicable global variables,
we don't need to duplicate the work in TargetMachine:shouldAssumeDSOLocal.
(Actually the long-term goal (started by r324535) is to remove as much
additional implied dso_local in TargetMachine:shouldAssumeDSOLocal as possible.)

By not implying dso_local, we will respect dso_local/dso_preemptable specifiers
set by the frontend. This allows the proposed -fno-direct-access-external-data
option to work with -fno-pic and prevent copy relocations.

This patch should be NFC in terms of the Clang behavior because the case we
don't set dso_local is a case Clang sets dso_local. However, some tests don't
set dso_local on some `external global` and expose some differences. Most tests
have been fixed to be more robust in previous commits.

Author: MaskRay

llvm/lib/Target/TargetMachine.cpp

@@ -190,9 +190,18 @@ bool TargetMachine::shouldAssumeDSOLocal(const Module &M,
     if (Arch == Triple::ppc || TT.isPPC64())
       return false;
 
-    // Check if we can use copy relocations.
-    if (!(GV && GV->isThreadLocal()) && RM == Reloc::Static)
-      return true;
+    // dso_local is traditionally implied for Reloc::Static. Eventually we shall
+    // drop the if block entirely and respect dso_local/dso_preemptable
+    // specifiers set by the frontend.
+    if (RM == Reloc::Static) {
+      // We currently respect dso_local/dso_preemptable specifiers for
+      // variables.
+      if (!GV || F)
+        return true;
+      // TODO Remove the special case for x86-32 and wasm.
+      if ((Arch == Triple::x86 || TT.isWasm()) && !GV->isThreadLocal())
+        return true;
+    }
   } else if (TT.isOSBinFormatELF()) {
     // If dso_local allows AsmPrinter::getSymbolPreferLocal to use a local
     // alias, set the flag. We cannot set dso_local for other global values,

llvm/test/CodeGen/AArch64/extern-weak.ll

@@ -39,12 +39,10 @@ define i32* @bar() {
 
   ret i32* %addr
 
-  ; In the large model, the usual relocations are absolute and can
-  ; materialise 0.
-; CHECK-LARGE: movz [[ADDR:x[0-9]+]], #:abs_g0_nc:arr_var
-; CHECK-LARGE: movk [[ADDR]], #:abs_g1_nc:arr_var
-; CHECK-LARGE: movk [[ADDR]], #:abs_g2_nc:arr_var
-; CHECK-LARGE: movk [[ADDR]], #:abs_g3:arr_var
+  ; Note, In the large model, if dso_local, the relocations are absolute and can materialise 0.
+; CHECK-LARGE:      adrp x[[ADDR:[0-9]+]], :got:arr_var
+; CHECK-LARGE-NEXT: ldr x[[ADDR]], [x[[ADDR]], :got_lo12:arr_var]
+; CHECK-LARGE-NEXT: add x0, x[[ADDR]], #20
 
 ; CHECK-TINY: ldr [[BASE:x[0-9]+]], :got:arr_var
 ; CHECK-TINY: add x0, [[BASE]], #20

llvm/test/CodeGen/AArch64/tiny_model.ll

@@ -15,17 +15,17 @@
 define void @foo1() {
 ; CHECK-LABEL: foo1:
 ; CHECK:       // %bb.0: // %entry
-; CHECK-NEXT:    adr x8, src
+; CHECK-NEXT:    ldr x8, :got:src
 ; CHECK-NEXT:    ldrb w8, [x8]
-; CHECK-NEXT:    adr x9, dst
+; CHECK-NEXT:    ldr x9, :got:dst
 ; CHECK-NEXT:    strb w8, [x9]
 ; CHECK-NEXT:    ret
 ;
 ; CHECK-GLOBISEL-LABEL: foo1:
 ; CHECK-GLOBISEL:       // %bb.0: // %entry
-; CHECK-GLOBISEL-NEXT:    adr x8, src
+; CHECK-GLOBISEL-NEXT:    ldr x8, :got:src
 ; CHECK-GLOBISEL-NEXT:    ldrb w8, [x8]
-; CHECK-GLOBISEL-NEXT:    adr x9, dst
+; CHECK-GLOBISEL-NEXT:    ldr x9, :got:dst
 ; CHECK-GLOBISEL-NEXT:    strb w8, [x9]
 ; CHECK-GLOBISEL-NEXT:    ret
 ;
@@ -53,15 +53,15 @@ entry:
 define void @foo2() {
 ; CHECK-LABEL: foo2:
 ; CHECK:       // %bb.0: // %entry
-; CHECK-NEXT:    adr x8, ptr
-; CHECK-NEXT:    adr x9, dst
+; CHECK-NEXT:    ldr x8, :got:ptr
+; CHECK-NEXT:    ldr x9, :got:dst
 ; CHECK-NEXT:    str x9, [x8]
 ; CHECK-NEXT:    ret
 ;
 ; CHECK-GLOBISEL-LABEL: foo2:
 ; CHECK-GLOBISEL:       // %bb.0: // %entry
-; CHECK-GLOBISEL-NEXT:    adr x8, ptr
-; CHECK-GLOBISEL-NEXT:    adr x9, dst
+; CHECK-GLOBISEL-NEXT:    ldr x8, :got:ptr
+; CHECK-GLOBISEL-NEXT:    ldr x9, :got:dst
 ; CHECK-GLOBISEL-NEXT:    str x9, [x8]
 ; CHECK-GLOBISEL-NEXT:    ret
 ;
@@ -88,16 +88,17 @@ define void @foo3() {
 ;
 ; CHECK-LABEL: foo3:
 ; CHECK:       // %bb.0: // %entry
-; CHECK-NEXT:    adr x8, src
+; CHECK-NEXT:    ldr x8, :got:src
+; CHECK-NEXT:    ldr x9, :got:ptr
 ; CHECK-NEXT:    ldrb w8, [x8]
-; CHECK-NEXT:    ldr x9, ptr
+; CHECK-NEXT:    ldr x9, [x9]
 ; CHECK-NEXT:    strb w8, [x9]
 ; CHECK-NEXT:    ret
 ;
 ; CHECK-GLOBISEL-LABEL: foo3:
 ; CHECK-GLOBISEL:       // %bb.0: // %entry
-; CHECK-GLOBISEL-NEXT:    adr x8, src
-; CHECK-GLOBISEL-NEXT:    adr x9, ptr
+; CHECK-GLOBISEL-NEXT:    ldr x8, :got:src
+; CHECK-GLOBISEL-NEXT:    ldr x9, :got:ptr
 ; CHECK-GLOBISEL-NEXT:    ldrb w8, [x8]
 ; CHECK-GLOBISEL-NEXT:    ldr x9, [x9]
 ; CHECK-GLOBISEL-NEXT:    strb w8, [x9]