[InstCombine] Preserve metadata from orig load in select fold. (#115605)

When replacing load with a select on the address with a select and 2
loads of the values, copy poison-generating metadata from the original
load to the newly created loads, which are placed at the same place as
the original loads. We cannot copy metadata that may trigger UB.

PR: #115605

Author: fhahn

llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp

@@ -1060,6 +1060,10 @@ Instruction *InstCombinerImpl::visitLoadInst(LoadInst &LI) {
         V1->setAtomic(LI.getOrdering(), LI.getSyncScopeID());
         V2->setAlignment(Alignment);
         V2->setAtomic(LI.getOrdering(), LI.getSyncScopeID());
+        // It is safe to copy any metadata that does not trigger UB. Copy any
+        // poison-generating metadata.
+        V1->copyMetadata(LI, Metadata::PoisonGeneratingIDs);
+        V2->copyMetadata(LI, Metadata::PoisonGeneratingIDs);
         return SelectInst::Create(SI->getCondition(), V1, V2);
       }
 

llvm/test/Transforms/InstCombine/loadstore-metadata.ll

@@ -186,12 +186,12 @@ entry:
   ret i32 %c
 }
 
-; FIXME: Should preserve none-UB metadata on loads.
+; Preserve none-UB metadata on loads.
 define ptr @preserve_load_metadata_after_select_transform1(i1 %c, ptr dereferenceable(8) %a, ptr dereferenceable(8) %b) {
 ; CHECK-LABEL: @preserve_load_metadata_after_select_transform1(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[B_VAL:%.*]] = load ptr, ptr [[B:%.*]], align 1
-; CHECK-NEXT:    [[A_VAL:%.*]] = load ptr, ptr [[A:%.*]], align 1
+; CHECK-NEXT:    [[B_VAL:%.*]] = load ptr, ptr [[B:%.*]], align 1, !nonnull [[META6]], !align [[META8]]
+; CHECK-NEXT:    [[A_VAL:%.*]] = load ptr, ptr [[A:%.*]], align 1, !nonnull [[META6]], !align [[META8]]
 ; CHECK-NEXT:    [[L_SEL:%.*]] = select i1 [[C:%.*]], ptr [[B_VAL]], ptr [[A_VAL]]
 ; CHECK-NEXT:    ret ptr [[L_SEL]]
 ;
@@ -201,12 +201,12 @@ entry:
   ret ptr %l.sel
 }
 
-; FIXME: Should preserve none-UB metadata on loads.
+; Preserve none-UB metadata on loads.
 define i32 @preserve_load_metadata_after_select_transform_range(i1 %c, ptr dereferenceable(8) %a, ptr dereferenceable(8) %b) {
 ; CHECK-LABEL: @preserve_load_metadata_after_select_transform_range(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[B_VAL:%.*]] = load i32, ptr [[B:%.*]], align 1
-; CHECK-NEXT:    [[A_VAL:%.*]] = load i32, ptr [[A:%.*]], align 1
+; CHECK-NEXT:    [[B_VAL:%.*]] = load i32, ptr [[B:%.*]], align 1, !range [[RNG10:![0-9]+]]
+; CHECK-NEXT:    [[A_VAL:%.*]] = load i32, ptr [[A:%.*]], align 1, !range [[RNG10]]
 ; CHECK-NEXT:    [[L_SEL:%.*]] = select i1 [[C:%.*]], i32 [[B_VAL]], i32 [[A_VAL]]
 ; CHECK-NEXT:    ret i32 [[L_SEL]]
 ;
@@ -294,7 +294,7 @@ define double @preserve_load_metadata_after_select_transform_metadata_missing_4(
 ; CHECK-LABEL: @preserve_load_metadata_after_select_transform_metadata_missing_4(
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[L_A:%.*]] = load double, ptr [[A:%.*]], align 8, !tbaa [[TBAA0]], !alias.scope [[META3]], !noalias [[META3]], !llvm.access.group [[META6]]
-; CHECK-NEXT:    [[L_B:%.*]] = load double, ptr [[B:%.*]], align 8, !tbaa [[TBAA0]], !alias.scope [[META10:![0-9]+]], !noalias [[META10]], !llvm.access.group [[ACC_GRP13:![0-9]+]]
+; CHECK-NEXT:    [[L_B:%.*]] = load double, ptr [[B:%.*]], align 8, !tbaa [[TBAA0]], !alias.scope [[META11:![0-9]+]], !noalias [[META11]], !llvm.access.group [[ACC_GRP14:![0-9]+]]
 ; CHECK-NEXT:    [[CMP_I:%.*]] = fcmp fast olt double [[L_A]], [[L_B]]
 ; CHECK-NEXT:    [[L_SEL:%.*]] = select i1 [[CMP_I]], double [[L_B]], double [[L_A]]
 ; CHECK-NEXT:    ret double [[L_SEL]]
@@ -337,8 +337,9 @@ entry:
 ; CHECK: [[META7]] = !{i32 1}
 ; CHECK: [[META8]] = !{i64 8}
 ; CHECK: [[ACC_GRP9]] = distinct !{}
-; CHECK: [[META10]] = !{[[META11:![0-9]+]]}
-; CHECK: [[META11]] = distinct !{[[META11]], [[META12:![0-9]+]]}
-; CHECK: [[META12]] = distinct !{[[META12]]}
-; CHECK: [[ACC_GRP13]] = distinct !{}
+; CHECK: [[RNG10]] = !{i32 0, i32 42}
+; CHECK: [[META11]] = !{[[META12:![0-9]+]]}
+; CHECK: [[META12]] = distinct !{[[META12]], [[META13:![0-9]+]]}
+; CHECK: [[META13]] = distinct !{[[META13]]}
+; CHECK: [[ACC_GRP14]] = distinct !{}
 ;.