[Inliner] Preserve maynotprogress function attribute

[atmnpatel]

Summary

When inlining a function with the maynotprogress function attribute,
semantically, the caller function must also inherit the maynotprogress
attribute.

[atmnpatel]

Renamed.

[atmnpatel]

On second thought, we don't need this for mustprogress. If the callee is` mustprogress`, the caller cannot become mustprogress as well without changing program behavior as a result of inlining.

[nikic]

Abandon this as no longer necessary for mustprogress?

[atmnpatel]

Yep I wasn't entirely sure before but I am now.

llvm/include/llvm/IR/Attributes.td

 
 /// Function only writes to memory.
 def WriteOnly : EnumAttr<"writeonly">;
 
 /// Zero extended before/after call.
 def ZExt : EnumAttr<"zeroext">;
 
 /// Function is permitted to not make Forward Progress.
-def MayNotProgress : TypeAttr<"maynotprogress">;
+def MustProgress : TypeAttr<"mustprogress">;
 
 /// Target-independent string attributes.
 def LessPreciseFPMAD : StrBoolAttr<"less-precise-fpmad">;
 def NoInfsFPMath : StrBoolAttr<"no-infs-fp-math">;
 def NoNansFPMath : StrBoolAttr<"no-nans-fp-math">;
 def NoSignedZerosFPMath : StrBoolAttr<"no-signed-zeros-fp-math">;
 def UnsafeFPMath : StrBoolAttr<"unsafe-fp-math">;
 def NoJumpTables : StrBoolAttr<"no-jump-tables">;

 def : MergeRule<"setOR<NoJumpTablesAttr>">;
 def : MergeRule<"setOR<ProfileSampleAccurateAttr>">;
 def : MergeRule<"setOR<SpeculativeLoadHardeningAttr>">;
 def : MergeRule<"adjustCallerSSPLevel">;
 def : MergeRule<"adjustCallerStackProbes">;
 def : MergeRule<"adjustCallerStackProbeSize">;
 def : MergeRule<"adjustMinLegalVectorWidth">;
 def : MergeRule<"adjustNullPointerValidAttr">;
+def : MergeRule<"setOR<MustProgressAttr>">;

llvm/test/Transforms/Inline/mustprogress.ll

+; RUN: opt -inline -S < %s | FileCheck %s
+
+;; Original C Code:
+;; void callee(int a, int b) {
+;;  for (;a < b;) ;
+;;  while(1) ;
+;; }
+;; void caller() {
+;;  callee(0, 5);
+;; }
+
+define void @callee(i32 %a, i32 %b) #0 {
+entry:
+  br label %for.cond
+for.cond:
+  %cmp = icmp slt i32 %a, %b
+  br i1 %cmp, label %for.body, label %for.end
+for.body:
+  br label %for.cond
+for.end:
+  br label %while.body
+while.body:
+  br label %while.body
+}
+
+; CHECK: define void @caller() [[ATTR0:#.*]] {
+; CHECK: entry:
+; CHECK:    br label %[[FOR_COND:.*]]
+; CHECK: [[FOR_COND]]:
+; CHECK:    br label %[[FOR_COND]]
+; CHECK:    ret void
+; CHECK: }
+
+define void @caller() {
+entry:
+  call void @callee(i32 0, i32 5)
+  ret void
+}
+
+; CHECK: attributes [[ATTR0]] = { mustprogress }
+
+attributes #0 = { mustprogress }