[IR] Use Min behavior for module flag "PIC Level"

Using Max for both "PIC Level" and "PIE Level" is inconsistent. PIC imposes less
restriction while PIE imposes more restriction. The result generally
picks the more restrictive behavior: Min for PIC.

This choice matches `ld -r`: a non-pic object and a pic object merge into a
result which should be treated as non-pic.

To allow linking "PIC Level" using Error/Max from old bitcode files, upgrade
Error/Max to Min.

Reviewed By: tejohnson

Differential Revision: https://reviews.llvm.org/D130531

clang/test/CodeGen/piclevels.c

@@ -4,9 +4,9 @@
 // RUN: %clang_cc1 -emit-llvm -pic-level 1 -pic-is-pie %s -o - | FileCheck %s -check-prefix=CHECK-SMALLPIC -check-prefix=CHECK-SMALLPIE
 
 // CHECK-BIGPIC: !llvm.module.flags = !{{{.*}}}
-// CHECK-BIGPIC: !{{[0-9]+}} = !{i32 7, !"PIC Level", i32 2}
+// CHECK-BIGPIC: ![[#]] = !{i32 8, !"PIC Level", i32 2}
 // CHECK-SMALLPIC: !llvm.module.flags = !{{{.*}}}
-// CHECK-SMALLPIC: !{{[0-9]+}} = !{i32 7, !"PIC Level", i32 1}
+// CHECK-SMALLPIC: ![[#]] = !{i32 8, !"PIC Level", i32 1}
 // CHECK-NOPIE-NOT: PIE Level
-// CHECK-BIGPIE: !{{[0-9]+}} = !{i32 7, !"PIE Level", i32 2}
-// CHECK-SMALLPIE: !{{[0-9]+}} = !{i32 7, !"PIE Level", i32 1}
+// CHECK-BIGPIE: ![[#]] = !{i32 7, !"PIE Level", i32 2}
+// CHECK-SMALLPIE: ![[#]] = !{i32 7, !"PIE Level", i32 1}

llvm/lib/IR/AutoUpgrade.cpp

@@ -4391,26 +4391,34 @@ bool llvm::UpgradeModuleFlags(Module &M) {
     MDString *ID = dyn_cast_or_null<MDString>(Op->getOperand(1));
     if (!ID)
       continue;
+    auto SetBehavior = [&](Module::ModFlagBehavior B) {
+      Metadata *Ops[3] = {ConstantAsMetadata::get(ConstantInt::get(
+                              Type::getInt32Ty(M.getContext()), B)),
+                          MDString::get(M.getContext(), ID->getString()),
+                          Op->getOperand(2)};
+      ModFlags->setOperand(I, MDNode::get(M.getContext(), Ops));
+      Changed = true;
+    };
+
     if (ID->getString() == "Objective-C Image Info Version")
       HasObjCFlag = true;
     if (ID->getString() == "Objective-C Class Properties")
       HasClassProperties = true;
-    // Upgrade PIC/PIE Module Flags. The module flag behavior for these two
-    // field was Error and now they are Max.
-    if (ID->getString() == "PIC Level" || ID->getString() == "PIE Level") {
+    // Upgrade PIC from Error/Max to Min.
+    if (ID->getString() == "PIC Level") {
       if (auto *Behavior =
               mdconst::dyn_extract_or_null<ConstantInt>(Op->getOperand(0))) {
-        if (Behavior->getLimitedValue() == Module::Error) {
-          Type *Int32Ty = Type::getInt32Ty(M.getContext());
-          Metadata *Ops[3] = {
-              ConstantAsMetadata::get(ConstantInt::get(Int32Ty, Module::Max)),
-              MDString::get(M.getContext(), ID->getString()),
-              Op->getOperand(2)};
-          ModFlags->setOperand(I, MDNode::get(M.getContext(), Ops));
-          Changed = true;
-        }
+        uint64_t V = Behavior->getLimitedValue();
+        if (V == Module::Error || V == Module::Max)
+          SetBehavior(Module::Min);
       }
     }
+    // Upgrade "PIE Level" from Error to Max.
+    if (ID->getString() == "PIE Level")
+      if (auto *Behavior =
+              mdconst::dyn_extract_or_null<ConstantInt>(Op->getOperand(0)))
+        if (Behavior->getLimitedValue() == Module::Error)
+          SetBehavior(Module::Max);
 
     // Upgrade branch protection and return address signing module flags. The
     // module flag behavior for these fields were Error and now they are Min.

llvm/lib/IR/Module.cpp

@@ -596,7 +596,9 @@ PICLevel::Level Module::getPICLevel() const {
 }
 
 void Module::setPICLevel(PICLevel::Level PL) {
-  addModuleFlag(ModFlagBehavior::Max, "PIC Level", PL);
+  // The merge result of a non-PIC object and a PIC object can only be reliably
+  // used as a non-PIC object, so use the Min merge behavior.
+  addModuleFlag(ModFlagBehavior::Min, "PIC Level", PL);
 }
 
 PIELevel::Level Module::getPIELevel() const {

llvm/test/Bitcode/upgrade-module-flag.ll

@@ -8,7 +8,7 @@
 !2 = !{i32 1, !"Objective-C Image Info Version", i32 0}
 !3 = !{i32 1, !"Objective-C Image Info Section", !"__DATA, __objc_imageinfo, regular, no_dead_strip"}
 
-; CHECK: !0 = !{i32 7, !"PIC Level", i32 1}
+; CHECK: !0 = !{i32 8, !"PIC Level", i32 1}
 ; CHECK: !1 = !{i32 7, !"PIE Level", i32 1}
 ; CHECK: !2 = !{i32 1, !"Objective-C Image Info Version", i32 0}
 ; CHECK: !3 = !{i32 1, !"Objective-C Image Info Section", !"__DATA,__objc_imageinfo,regular,no_dead_strip"}

llvm/test/Bitcode/upgrade-pic-level.ll

@@ -0,0 +1,8 @@
+; RUN: llvm-as < %s | llvm-dis | FileCheck %s
+; RUN: verify-uselistorder < %s
+
+!llvm.module.flags = !{!0}
+
+; CHECK: !0 = !{i32 8, !"PIC Level", i32 1}
+
+!0 = !{i32 7, !"PIC Level", i32 1}

llvm/test/Linker/Inputs/module-flags-pic-2-b.ll

@@ -1,4 +1,4 @@
-!0 = !{ i32 7, !"PIC Level", i32 2 }
+!0 = !{ i32 8, !"PIC Level", i32 2 }
 !1 = !{ i32 7, !"PIE Level", i32 2 }
 
 !llvm.module.flags = !{!0, !1}

llvm/test/Linker/module-flags-pic-1-a.ll

@@ -6,4 +6,4 @@
 
 !llvm.module.flags = !{!0}
 ; CHECK: !llvm.module.flags = !{!0}
-; CHECK: !0 = !{i32 7, !"PIC Level", i32 1}
+; CHECK: !0 = !{i32 8, !"PIC Level", i32 1}

llvm/test/Linker/module-flags-pic-2-a.ll

@@ -2,10 +2,10 @@
 
 ; test linking modules with two different PIC and PIE levels
 
-!0 = !{ i32 7, !"PIC Level", i32 1 }
+!0 = !{ i32 8, !"PIC Level", i32 1 }
 !1 = !{ i32 7, !"PIE Level", i32 1 }
 
 !llvm.module.flags = !{!0, !1}
 
-; CHECK: !0 = !{i32 7, !"PIC Level", i32 2}
+; CHECK: !0 = !{i32 8, !"PIC Level", i32 1}
 ; CHECK: !1 = !{i32 7, !"PIE Level", i32 2}

llvm/test/Transforms/Attributor/value-simplify-dbg.ll

@@ -58,7 +58,7 @@ declare i32 @speculatable() speculatable readnone
 !7 = !{i32 7, !"Dwarf Version", i32 5}
 !8 = !{i32 2, !"Debug Info Version", i32 3}
 !9 = !{i32 1, !"wchar_size", i32 4}
-!10 = !{i32 7, !"PIC Level", i32 2}
+!10 = !{i32 8, !"PIC Level", i32 2}
 !11 = !{i32 7, !"PIE Level", i32 2}
 !12 = !{i32 7, !"uwtable", i32 2}
 !13 = !{i32 7, !"frame-pointer", i32 2}
@@ -88,7 +88,7 @@ declare i32 @speculatable() speculatable readnone
 ; CHECK: [[META7:![0-9]+]] = !{i32 7, !"Dwarf Version", i32 5}
 ; CHECK: [[META8:![0-9]+]] = !{i32 2, !"Debug Info Version", i32 3}
 ; CHECK: [[META9:![0-9]+]] = !{i32 1, !"wchar_size", i32 4}
-; CHECK: [[META10:![0-9]+]] = !{i32 7, !"PIC Level", i32 2}
+; CHECK: [[META10:![0-9]+]] = !{i32 8, !"PIC Level", i32 2}
 ; CHECK: [[META11:![0-9]+]] = !{i32 7, !"PIE Level", i32 2}
 ; CHECK: [[META12:![0-9]+]] = !{i32 7, !"uwtable", i32 2}
 ; CHECK: [[META13:![0-9]+]] = !{i32 7, !"frame-pointer", i32 2}

llvm/test/Transforms/Attributor/value-simplify-local-remote.ll

@@ -769,7 +769,7 @@ entry:
 !1 = !{i32 1, !"wchar_size", i32 4}
 !2 = !{i32 7, !"openmp", i32 50}
 !3 = !{i32 7, !"openmp-device", i32 50}
-!4 = !{i32 7, !"PIC Level", i32 2}
+!4 = !{i32 8, !"PIC Level", i32 2}
 !5 = !{i32 7, !"frame-pointer", i32 2}
 !6 = !{i32 7, !"Dwarf Version", i32 2}
 !7 = !{i32 2, !"Debug Info Version", i32 3}
@@ -795,7 +795,7 @@ entry:
 ; CHECK: [[META1:![0-9]+]] = !{i32 1, !"wchar_size", i32 4}
 ; CHECK: [[META2:![0-9]+]] = !{i32 7, !"openmp", i32 50}
 ; CHECK: [[META3:![0-9]+]] = !{i32 7, !"openmp-device", i32 50}
-; CHECK: [[META4:![0-9]+]] = !{i32 7, !"PIC Level", i32 2}
+; CHECK: [[META4:![0-9]+]] = !{i32 8, !"PIC Level", i32 2}
 ; CHECK: [[META5:![0-9]+]] = !{i32 7, !"frame-pointer", i32 2}
 ; CHECK: [[META6:![0-9]+]] = !{i32 7, !"Dwarf Version", i32 2}
 ; CHECK: [[META7:![0-9]+]] = !{i32 2, !"Debug Info Version", i32 3}

llvm/test/Transforms/OpenMP/spmdization.ll

@@ -2395,7 +2395,7 @@ attributes #11 = { convergent }
 !12 = !{i32 1, !"wchar_size", i32 4}
 !13 = !{i32 7, !"openmp", i32 50}
 !14 = !{i32 7, !"openmp-device", i32 50}
-!15 = !{i32 7, !"PIC Level", i32 2}
+!15 = !{i32 8, !"PIC Level", i32 2}
 !16 = !{i32 7, !"frame-pointer", i32 2}
 !17 = !{!"clang version 14.0.0"}
 !18 = !{!19, !19, i64 0}
@@ -2481,7 +2481,7 @@ attributes #11 = { convergent }
 ; AMDGPU: [[META12:![0-9]+]] = !{i32 1, !"wchar_size", i32 4}
 ; AMDGPU: [[META13:![0-9]+]] = !{i32 7, !"openmp", i32 50}
 ; AMDGPU: [[META14:![0-9]+]] = !{i32 7, !"openmp-device", i32 50}
-; AMDGPU: [[META15:![0-9]+]] = !{i32 7, !"PIC Level", i32 2}
+; AMDGPU: [[META15:![0-9]+]] = !{i32 8, !"PIC Level", i32 2}
 ; AMDGPU: [[META16:![0-9]+]] = !{i32 7, !"frame-pointer", i32 2}
 ; AMDGPU: [[META17:![0-9]+]] = !{!"clang version 14.0.0"}
 ; AMDGPU: [[TBAA18]] = !{!19, !19, i64 0}
@@ -2515,7 +2515,7 @@ attributes #11 = { convergent }
 ; NVPTX: [[META12:![0-9]+]] = !{i32 1, !"wchar_size", i32 4}
 ; NVPTX: [[META13:![0-9]+]] = !{i32 7, !"openmp", i32 50}
 ; NVPTX: [[META14:![0-9]+]] = !{i32 7, !"openmp-device", i32 50}
-; NVPTX: [[META15:![0-9]+]] = !{i32 7, !"PIC Level", i32 2}
+; NVPTX: [[META15:![0-9]+]] = !{i32 8, !"PIC Level", i32 2}
 ; NVPTX: [[META16:![0-9]+]] = !{i32 7, !"frame-pointer", i32 2}
 ; NVPTX: [[META17:![0-9]+]] = !{!"clang version 14.0.0"}
 ; NVPTX: [[TBAA18]] = !{!19, !19, i64 0}
@@ -2549,7 +2549,7 @@ attributes #11 = { convergent }
 ; AMDGPU-DISABLED: [[META12:![0-9]+]] = !{i32 1, !"wchar_size", i32 4}
 ; AMDGPU-DISABLED: [[META13:![0-9]+]] = !{i32 7, !"openmp", i32 50}
 ; AMDGPU-DISABLED: [[META14:![0-9]+]] = !{i32 7, !"openmp-device", i32 50}
-; AMDGPU-DISABLED: [[META15:![0-9]+]] = !{i32 7, !"PIC Level", i32 2}
+; AMDGPU-DISABLED: [[META15:![0-9]+]] = !{i32 8, !"PIC Level", i32 2}
 ; AMDGPU-DISABLED: [[META16:![0-9]+]] = !{i32 7, !"frame-pointer", i32 2}
 ; AMDGPU-DISABLED: [[META17:![0-9]+]] = !{!"clang version 14.0.0"}
 ; AMDGPU-DISABLED: [[TBAA18]] = !{!19, !19, i64 0}
@@ -2583,7 +2583,7 @@ attributes #11 = { convergent }
 ; NVPTX-DISABLED: [[META12:![0-9]+]] = !{i32 1, !"wchar_size", i32 4}
 ; NVPTX-DISABLED: [[META13:![0-9]+]] = !{i32 7, !"openmp", i32 50}
 ; NVPTX-DISABLED: [[META14:![0-9]+]] = !{i32 7, !"openmp-device", i32 50}
-; NVPTX-DISABLED: [[META15:![0-9]+]] = !{i32 7, !"PIC Level", i32 2}
+; NVPTX-DISABLED: [[META15:![0-9]+]] = !{i32 8, !"PIC Level", i32 2}
 ; NVPTX-DISABLED: [[META16:![0-9]+]] = !{i32 7, !"frame-pointer", i32 2}
 ; NVPTX-DISABLED: [[META17:![0-9]+]] = !{!"clang version 14.0.0"}
 ; NVPTX-DISABLED: [[TBAA18]] = !{!19, !19, i64 0}

llvm/test/Transforms/OpenMP/spmdization_assumes.ll

@@ -137,7 +137,7 @@ attributes #6 = { convergent nounwind "llvm.assume"="ompx_spmd_amenable" }
 !2 = !{i32 1, !"wchar_size", i32 4}
 !3 = !{i32 7, !"openmp", i32 50}
 !4 = !{i32 7, !"openmp-device", i32 50}
-!5 = !{i32 7, !"PIC Level", i32 2}
+!5 = !{i32 8, !"PIC Level", i32 2}
 !6 = !{i32 7, !"frame-pointer", i32 2}
 !7 = !{!"clang version 14.0.0"}
 !8 = !{!9, !9, i64 0}
@@ -159,7 +159,7 @@ attributes #6 = { convergent nounwind "llvm.assume"="ompx_spmd_amenable" }
 ; CHECK: [[META2:![0-9]+]] = !{i32 1, !"wchar_size", i32 4}
 ; CHECK: [[META3:![0-9]+]] = !{i32 7, !"openmp", i32 50}
 ; CHECK: [[META4:![0-9]+]] = !{i32 7, !"openmp-device", i32 50}
-; CHECK: [[META5:![0-9]+]] = !{i32 7, !"PIC Level", i32 2}
+; CHECK: [[META5:![0-9]+]] = !{i32 8, !"PIC Level", i32 2}
 ; CHECK: [[META6:![0-9]+]] = !{i32 7, !"frame-pointer", i32 2}
 ; CHECK: [[META7:![0-9]+]] = !{!"clang version 14.0.0"}
 ; CHECK: [[TBAA8]] = !{!9, !9, i64 0}

llvm/test/Transforms/OpenMP/spmdization_guarding.ll

@@ -381,7 +381,7 @@ attributes #5 = { convergent nounwind "llvm.assume"="omp_no_openmp,ompx_spmd_ame
 !2 = !{i32 1, !"wchar_size", i32 4}
 !3 = !{i32 7, !"openmp", i32 50}
 !4 = !{i32 7, !"openmp-device", i32 50}
-!5 = !{i32 7, !"PIC Level", i32 2}
+!5 = !{i32 8, !"PIC Level", i32 2}
 !6 = !{i32 7, !"frame-pointer", i32 2}
 !7 = !{!"clang version 14.0.0"}
 !8 = !{!9}
@@ -419,7 +419,7 @@ attributes #5 = { convergent nounwind "llvm.assume"="omp_no_openmp,ompx_spmd_ame
 ; CHECK: [[META2:![0-9]+]] = !{i32 1, !"wchar_size", i32 4}
 ; CHECK: [[META3:![0-9]+]] = !{i32 7, !"openmp", i32 50}
 ; CHECK: [[META4:![0-9]+]] = !{i32 7, !"openmp-device", i32 50}
-; CHECK: [[META5:![0-9]+]] = !{i32 7, !"PIC Level", i32 2}
+; CHECK: [[META5:![0-9]+]] = !{i32 8, !"PIC Level", i32 2}
 ; CHECK: [[META6:![0-9]+]] = !{i32 7, !"frame-pointer", i32 2}
 ; CHECK: [[META7:![0-9]+]] = !{!"clang version 14.0.0"}
 ; CHECK: [[META8:![0-9]+]] = !{!9}
@@ -433,7 +433,7 @@ attributes #5 = { convergent nounwind "llvm.assume"="omp_no_openmp,ompx_spmd_ame
 ; CHECK-DISABLED: [[META2:![0-9]+]] = !{i32 1, !"wchar_size", i32 4}
 ; CHECK-DISABLED: [[META3:![0-9]+]] = !{i32 7, !"openmp", i32 50}
 ; CHECK-DISABLED: [[META4:![0-9]+]] = !{i32 7, !"openmp-device", i32 50}
-; CHECK-DISABLED: [[META5:![0-9]+]] = !{i32 7, !"PIC Level", i32 2}
+; CHECK-DISABLED: [[META5:![0-9]+]] = !{i32 8, !"PIC Level", i32 2}
 ; CHECK-DISABLED: [[META6:![0-9]+]] = !{i32 7, !"frame-pointer", i32 2}
 ; CHECK-DISABLED: [[META7:![0-9]+]] = !{!"clang version 14.0.0"}
 ; CHECK-DISABLED: [[META8:![0-9]+]] = !{!9}

llvm/test/Transforms/OpenMP/spmdization_guarding_two_reaching_kernels.ll

@@ -265,7 +265,7 @@ attributes #5 = { convergent }
 !4 = !{i32 1, !"wchar_size", i32 4}
 !5 = !{i32 7, !"openmp", i32 50}
 !6 = !{i32 7, !"openmp-device", i32 50}
-!7 = !{i32 7, !"PIC Level", i32 2}
+!7 = !{i32 8, !"PIC Level", i32 2}
 !8 = !{i32 7, !"frame-pointer", i32 2}
 !9 = !{!"clang version 14.0.0"}
 ;.
@@ -285,7 +285,7 @@ attributes #5 = { convergent }
 ; CHECK: [[META4:![0-9]+]] = !{i32 1, !"wchar_size", i32 4}
 ; CHECK: [[META5:![0-9]+]] = !{i32 7, !"openmp", i32 50}
 ; CHECK: [[META6:![0-9]+]] = !{i32 7, !"openmp-device", i32 50}
-; CHECK: [[META7:![0-9]+]] = !{i32 7, !"PIC Level", i32 2}
+; CHECK: [[META7:![0-9]+]] = !{i32 8, !"PIC Level", i32 2}
 ; CHECK: [[META8:![0-9]+]] = !{i32 7, !"frame-pointer", i32 2}
 ; CHECK: [[META9:![0-9]+]] = !{!"clang version 14.0.0"}
 ;.