[FunctionAttrs] Fix incorrect nonnull inference for non-inbounds GEP (#91180)

For inbounds GEPs, if the source pointer is non-null, the result must
also be non-null. However, this does not hold for non-inbounds GEPs.

Fixes #91177.

(cherry picked from commit f34d30c)

Author: nikic

llvm/lib/Transforms/IPO/FunctionAttrs.cpp

@@ -1186,10 +1186,15 @@ static bool isReturnNonNull(Function *F, const SCCNodeSet &SCCNodes,
     switch (RVI->getOpcode()) {
     // Extend the analysis by looking upwards.
     case Instruction::BitCast:
-    case Instruction::GetElementPtr:
     case Instruction::AddrSpaceCast:
       FlowsToReturn.insert(RVI->getOperand(0));
       continue;
+    case Instruction::GetElementPtr:
+      if (cast<GEPOperator>(RVI)->isInBounds()) {
+        FlowsToReturn.insert(RVI->getOperand(0));
+        continue;
+      }
+      return false;
     case Instruction::Select: {
       SelectInst *SI = cast<SelectInst>(RVI);
       FlowsToReturn.insert(SI->getTrueValue());

llvm/test/Transforms/FunctionAttrs/nocapture.ll

@@ -197,7 +197,7 @@ declare i32 @__gxx_personality_v0(...)
 
 define ptr @lookup_bit(ptr %q, i32 %bitno) readnone nounwind {
 ; FNATTRS: Function Attrs: mustprogress nofree norecurse nosync nounwind willreturn memory(none)
-; FNATTRS-LABEL: define nonnull ptr @lookup_bit
+; FNATTRS-LABEL: define ptr @lookup_bit
 ; FNATTRS-SAME: (ptr [[Q:%.*]], i32 [[BITNO:%.*]]) #[[ATTR0]] {
 ; FNATTRS-NEXT:    [[TMP:%.*]] = ptrtoint ptr [[Q]] to i32
 ; FNATTRS-NEXT:    [[TMP2:%.*]] = lshr i32 [[TMP]], [[BITNO]]

llvm/test/Transforms/FunctionAttrs/nonnull.ll

@@ -905,26 +905,26 @@ define i1 @parent8(ptr %a, ptr %bogus1, ptr %b) personality ptr @esfp{
 ; FNATTRS-SAME: ptr nonnull [[A:%.*]], ptr nocapture readnone [[BOGUS1:%.*]], ptr nonnull [[B:%.*]]) #[[ATTR7]] personality ptr @esfp {
 ; FNATTRS-NEXT:  entry:
 ; FNATTRS-NEXT:    invoke void @use2nonnull(ptr [[A]], ptr [[B]])
-; FNATTRS-NEXT:    to label [[CONT:%.*]] unwind label [[EXC:%.*]]
+; FNATTRS-NEXT:            to label [[CONT:%.*]] unwind label [[EXC:%.*]]
 ; FNATTRS:       cont:
 ; FNATTRS-NEXT:    [[NULL_CHECK:%.*]] = icmp eq ptr [[B]], null
 ; FNATTRS-NEXT:    ret i1 [[NULL_CHECK]]
 ; FNATTRS:       exc:
 ; FNATTRS-NEXT:    [[LP:%.*]] = landingpad { ptr, i32 }
-; FNATTRS-NEXT:    filter [0 x ptr] zeroinitializer
+; FNATTRS-NEXT:            filter [0 x ptr] zeroinitializer
 ; FNATTRS-NEXT:    unreachable
 ;
 ; ATTRIBUTOR-LABEL: define i1 @parent8(
 ; ATTRIBUTOR-SAME: ptr nonnull [[A:%.*]], ptr nocapture nofree readnone [[BOGUS1:%.*]], ptr nonnull [[B:%.*]]) #[[ATTR8]] personality ptr @esfp {
 ; ATTRIBUTOR-NEXT:  entry:
 ; ATTRIBUTOR-NEXT:    invoke void @use2nonnull(ptr nonnull [[A]], ptr nonnull [[B]])
-; ATTRIBUTOR-NEXT:    to label [[CONT:%.*]] unwind label [[EXC:%.*]]
+; ATTRIBUTOR-NEXT:            to label [[CONT:%.*]] unwind label [[EXC:%.*]]
 ; ATTRIBUTOR:       cont:
 ; ATTRIBUTOR-NEXT:    [[NULL_CHECK:%.*]] = icmp eq ptr [[B]], null
 ; ATTRIBUTOR-NEXT:    ret i1 [[NULL_CHECK]]
 ; ATTRIBUTOR:       exc:
 ; ATTRIBUTOR-NEXT:    [[LP:%.*]] = landingpad { ptr, i32 }
-; ATTRIBUTOR-NEXT:    filter [0 x ptr] zeroinitializer
+; ATTRIBUTOR-NEXT:            filter [0 x ptr] zeroinitializer
 ; ATTRIBUTOR-NEXT:    unreachable
 ;
 
@@ -1415,5 +1415,20 @@ define void @PR43833_simple(ptr %0, i32 %1) {
   br i1 %11, label %7, label %8
 }
 
+define ptr @pr91177_non_inbounds_gep(ptr nonnull %arg) {
+; FNATTRS-LABEL: define ptr @pr91177_non_inbounds_gep(
+; FNATTRS-SAME: ptr nonnull readnone [[ARG:%.*]]) #[[ATTR0]] {
+; FNATTRS-NEXT:    [[RES:%.*]] = getelementptr i8, ptr [[ARG]], i64 -8
+; FNATTRS-NEXT:    ret ptr [[RES]]
+;
+; ATTRIBUTOR-LABEL: define ptr @pr91177_non_inbounds_gep(
+; ATTRIBUTOR-SAME: ptr nofree nonnull readnone [[ARG:%.*]]) #[[ATTR0]] {
+; ATTRIBUTOR-NEXT:    [[RES:%.*]] = getelementptr i8, ptr [[ARG]], i64 -8
+; ATTRIBUTOR-NEXT:    ret ptr [[RES]]
+;
+  %res = getelementptr i8, ptr %arg, i64 -8
+  ret ptr %res
+}
+
 attributes #0 = { null_pointer_is_valid }
 attributes #1 = { nounwind willreturn}