[VPlan] Remove dead recipes before simplifying blends (#157622)

In simplifyBlends, when normalizing a blend recipe, the first mask that
is used only by the blend and is not all-false is chosen, and its
corresponding incoming value becomes the initial value, with the others
blended into it. At the same time, the mask that is chosen can be
eliminated. However, a multi-user mask might be used by a dead recipe,
which prevents this optimization. This patch moves removeDeadRecipes
before simplifyBlends to eliminate dead recipes, allowing simplifyBlends
to remove more dead masks.

Author: Mel-Chen

llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp

@@ -2215,8 +2215,8 @@ void VPlanTransforms::optimize(VPlan &Plan) {
   runPass(removeRedundantInductionCasts, Plan);
 
   runPass(simplifyRecipes, Plan);
-  runPass(simplifyBlends, Plan);
   runPass(removeDeadRecipes, Plan);
+  runPass(simplifyBlends, Plan);
   runPass(narrowToSingleScalarRecipes, Plan);
   runPass(legalizeAndOptimizeInductions, Plan);
   runPass(removeRedundantExpandSCEVRecipes, Plan);

llvm/test/Transforms/LoopVectorize/if-pred-non-void.ll

@@ -562,9 +562,7 @@ define void @pr30172(ptr nocapture %asd, ptr nocapture %bsd) !dbg !5 {;
 ; CHECK-NEXT:    br label [[PRED_SDIV_CONTINUE4]]
 ; CHECK:       pred.sdiv.continue4:
 ; CHECK-NEXT:    [[TMP28:%.*]] = phi <2 x i32> [ [[TMP19]], [[PRED_SDIV_CONTINUE]] ], [ [[TMP26]], [[PRED_SDIV_IF3]] ]
-; CHECK-NEXT:    [[TMP27:%.*]] = xor <2 x i1> [[TMP8]], splat (i1 true), !dbg [[DBG35]]
-; CHECK-NEXT:    [[TMP30:%.*]] = select <2 x i1> [[TMP4]], <2 x i1> [[TMP27]], <2 x i1> zeroinitializer, !dbg [[DBG35]]
-; CHECK-NEXT:    [[PREDPHI:%.*]] = select <2 x i1> [[TMP30]], <2 x i32> [[TMP5]], <2 x i32> [[TMP28]]
+; CHECK-NEXT:    [[PREDPHI:%.*]] = select <2 x i1> [[TMP10]], <2 x i32> [[TMP28]], <2 x i32> [[TMP5]]
 ; CHECK-NEXT:    store <2 x i32> [[PREDPHI]], ptr [[TMP1]], align 4, !alias.scope [[META29]], !noalias [[META32]]
 ; CHECK-NEXT:    [[INDEX_NEXT]] = add nuw i64 [[INDEX]], 2
 ; CHECK-NEXT:    [[TMP32:%.*]] = icmp eq i64 [[INDEX_NEXT]], 128
@@ -642,12 +640,8 @@ define void @pr30172(ptr nocapture %asd, ptr nocapture %bsd) !dbg !5 {;
 ; UNROLL-NO-VF-NEXT:    br label [[PRED_SDIV_CONTINUE3]]
 ; UNROLL-NO-VF:       pred.sdiv.continue3:
 ; UNROLL-NO-VF-NEXT:    [[TMP29:%.*]] = phi i32 [ poison, [[PRED_SDIV_CONTINUE]] ], [ [[TMP27]], [[PRED_SDIV_IF2]] ]
-; UNROLL-NO-VF-NEXT:    [[TMP30:%.*]] = xor i1 [[TMP15]], true, !dbg [[DBG35]]
-; UNROLL-NO-VF-NEXT:    [[TMP28:%.*]] = xor i1 [[TMP16]], true, !dbg [[DBG35]]
-; UNROLL-NO-VF-NEXT:    [[TMP32:%.*]] = select i1 [[TMP17]], i1 [[TMP30]], i1 false, !dbg [[DBG35]]
-; UNROLL-NO-VF-NEXT:    [[TMP33:%.*]] = select i1 [[TMP14]], i1 [[TMP28]], i1 false, !dbg [[DBG35]]
-; UNROLL-NO-VF-NEXT:    [[PREDPHI:%.*]] = select i1 [[TMP32]], i32 [[TMP10]], i32 [[TMP25]]
-; UNROLL-NO-VF-NEXT:    [[PREDPHI4:%.*]] = select i1 [[TMP33]], i32 [[TMP11]], i32 [[TMP29]]
+; UNROLL-NO-VF-NEXT:    [[PREDPHI:%.*]] = select i1 [[TMP20]], i32 [[TMP25]], i32 [[TMP10]]
+; UNROLL-NO-VF-NEXT:    [[PREDPHI4:%.*]] = select i1 [[TMP21]], i32 [[TMP29]], i32 [[TMP11]]
 ; UNROLL-NO-VF-NEXT:    store i32 [[PREDPHI]], ptr [[TMP2]], align 4, !alias.scope [[META29]], !noalias [[META32]]
 ; UNROLL-NO-VF-NEXT:    store i32 [[PREDPHI4]], ptr [[TMP3]], align 4, !alias.scope [[META29]], !noalias [[META32]]
 ; UNROLL-NO-VF-NEXT:    [[INDEX_NEXT]] = add nuw i64 [[INDEX]], 2

llvm/test/Transforms/LoopVectorize/vplan-printing.ll

@@ -374,9 +374,7 @@ define void @debug_loc_vpinstruction(ptr nocapture %asd, ptr nocapture %bsd) !db
 ; CHECK-NEXT:  Successor(s): if.then.0
 ; CHECK-EMPTY:
 ; CHECK-NEXT:  if.then.0:
-; CHECK-NEXT:    EMIT vp<[[NOT2:%.+]]> = not ir<%cmp2>
-; CHECK-NEXT:    EMIT vp<[[SEL2:%.+]]> = logical-and vp<[[NOT1]]>, vp<[[NOT2]]>
-; CHECK-NEXT:    BLEND ir<%ysd.0> = vp<[[PHI]]> ir<%psd>/vp<[[SEL2]]>
+; CHECK-NEXT:    BLEND ir<%ysd.0> = ir<%psd> vp<[[PHI]]>/vp<[[OR1]]>
 ; CHECK-NEXT:    vp<[[VEC_PTR2:%.+]]> = vector-pointer ir<%isd>
 ; CHECK-NEXT:    WIDEN store vp<[[VEC_PTR2]]>, ir<%ysd.0>
 ; CHECK-NEXT:    EMIT vp<[[CAN_IV_NEXT]]> = add nuw vp<[[CAN_IV]]>, vp<[[VFxUF]]>