[GVN] Excluding dead blocks before full redundancy eliminations

llvm/lib/Transforms/Scalar/GVN.cpp

@@ -1888,6 +1888,17 @@ bool GVNPass::processNonLocalLoad(LoadInst *Load) {
   // load, then it is fully redundant and we can use PHI insertion to compute
   // its value.  Insert PHIs and remove the fully redundant value now.
   if (UnavailableBlocks.empty()) {
+    // Excluding dead blocks, whose available values are undef. Note that we
+    // can't do this removal for partial redundancy.
+    auto AVEndIt = ValuesPerBlock.end();
+    auto AVBeginIt =
+        llvm::remove_if(ValuesPerBlock, [](const auto &AV) -> bool {
+          return AV.AV.isUndefValue();
+        });
+    ValuesPerBlock.erase(AVBeginIt, AVEndIt);
+    if (ValuesPerBlock.empty())
+      return Changed;
+
     LLVM_DEBUG(dbgs() << "GVN REMOVING NONLOCAL LOAD: " << *Load << '\n');
 
     // Perform PHI construction.

llvm/test/Transforms/GVN/pr88051.ll

@@ -0,0 +1,91 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 4
+; RUN: opt -S --passes='gvn' < %s | FileCheck %s
+
+@g = external global i32
+@e = external global [1 x i32]
+
+define signext i32 @main() nounwind {
+; CHECK-LABEL: define signext i32 @main(
+; CHECK-SAME: ) #[[ATTR0:[0-9]+]] {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label [[WHILE_BODY:%.*]]
+; CHECK:       while.body:
+; CHECK-NEXT:    [[DOTPRE15:%.*]] = phi i32 [ [[DOTPRE16:%.*]], [[FOR_END54:%.*]] ], [ undef, [[ENTRY:%.*]] ]
+; CHECK-NEXT:    [[DOTPRE2:%.*]] = phi i32 [ [[DOTPRE3:%.*]], [[FOR_END54]] ], [ undef, [[ENTRY]] ]
+; CHECK-NEXT:    [[TMP0:%.*]] = phi i32 [ [[TMP3:%.*]], [[FOR_END54]] ], [ undef, [[ENTRY]] ]
+; CHECK-NEXT:    [[TMP1:%.*]] = phi i32 [ [[TMP4:%.*]], [[FOR_END54]] ], [ undef, [[ENTRY]] ]
+; CHECK-NEXT:    br label [[FOR_BODY3:%.*]]
+; CHECK:       for.body3:
+; CHECK-NEXT:    br i1 false, label [[IF_ELSE:%.*]], label [[FOR_COND6_PREHEADER:%.*]]
+; CHECK:       for.cond6.preheader:
+; CHECK-NEXT:    br label [[IF_END49:%.*]]
+; CHECK:       if.else:
+; CHECK-NEXT:    [[TMP2:%.*]] = load ptr, ptr null, align 8
+; CHECK-NEXT:    store volatile i32 0, ptr [[TMP2]], align 4
+; CHECK-NEXT:    br i1 false, label [[IF_END:%.*]], label [[FOR_END54SPLITSPLIT:%.*]]
+; CHECK:       if.end:
+; CHECK-NEXT:    br i1 false, label [[IF_END_IF_END49_CRIT_EDGE:%.*]], label [[IF_END_FOR_END54_CRIT_EDGE:%.*]]
+; CHECK:       if.end.if.end49_crit_edge:
+; CHECK-NEXT:    br label [[IF_END49]]
+; CHECK:       if.end.for.end54_crit_edge:
+; CHECK-NEXT:    [[DOTPRE9:%.*]] = sext i32 [[TMP1]] to i64
+; CHECK-NEXT:    br label [[FOR_END54]]
+; CHECK:       if.end49:
+; CHECK-NEXT:    br i1 true, label [[FOR_BODY3]], label [[IF_END49_FOR_END54SPLIT_CRIT_EDGE:%.*]]
+; CHECK:       if.end49.for.end54split_crit_edge:
+; CHECK-NEXT:    [[DOTPRE_PRE:%.*]] = load i32, ptr @g, align 4
+; CHECK-NEXT:    [[DOTPRE8:%.*]] = sext i32 [[DOTPRE_PRE]] to i64
+; CHECK-NEXT:    br label [[FOR_END54SPLIT:%.*]]
+; CHECK:       for.end54splitsplit:
+; CHECK-NEXT:    [[IDXPROM55_PHI_TRANS_INSERT_PHI_TRANS_INSERT:%.*]] = sext i32 [[DOTPRE2]] to i64
+; CHECK-NEXT:    [[ARRAYIDX56_PHI_TRANS_INSERT_PHI_TRANS_INSERT:%.*]] = getelementptr inbounds [1 x i32], ptr @e, i64 0, i64 [[IDXPROM55_PHI_TRANS_INSERT_PHI_TRANS_INSERT]]
+; CHECK-NEXT:    [[DOTPRE1_PRE:%.*]] = load i32, ptr [[ARRAYIDX56_PHI_TRANS_INSERT_PHI_TRANS_INSERT]], align 4
+; CHECK-NEXT:    br label [[FOR_END54SPLIT]]
+; CHECK:       for.end54split:
+; CHECK-NEXT:    [[IDXPROM55_PHI_TRANS_INSERT_PRE_PHI:%.*]] = phi i64 [ [[IDXPROM55_PHI_TRANS_INSERT_PHI_TRANS_INSERT]], [[FOR_END54SPLITSPLIT]] ], [ [[DOTPRE8]], [[IF_END49_FOR_END54SPLIT_CRIT_EDGE]] ]
+; CHECK-NEXT:    [[DOTPRE1:%.*]] = phi i32 [ [[DOTPRE1_PRE]], [[FOR_END54SPLITSPLIT]] ], [ [[DOTPRE15]], [[IF_END49_FOR_END54SPLIT_CRIT_EDGE]] ]
+; CHECK-NEXT:    [[DOTPRE:%.*]] = phi i32 [ [[DOTPRE2]], [[FOR_END54SPLITSPLIT]] ], [ [[DOTPRE_PRE]], [[IF_END49_FOR_END54SPLIT_CRIT_EDGE]] ]
+; CHECK-NEXT:    [[ARRAYIDX56_PHI_TRANS_INSERT:%.*]] = getelementptr inbounds [1 x i32], ptr @e, i64 0, i64 [[IDXPROM55_PHI_TRANS_INSERT_PRE_PHI]]
+; CHECK-NEXT:    br label [[FOR_END54]]
+; CHECK:       for.end54:
+; CHECK-NEXT:    [[IDXPROM55_PRE_PHI:%.*]] = phi i64 [ [[IDXPROM55_PHI_TRANS_INSERT_PRE_PHI]], [[FOR_END54SPLIT]] ], [ [[DOTPRE9]], [[IF_END_FOR_END54_CRIT_EDGE]] ]
+; CHECK-NEXT:    [[DOTPRE16]] = phi i32 [ [[DOTPRE1]], [[FOR_END54SPLIT]] ], [ [[DOTPRE15]], [[IF_END_FOR_END54_CRIT_EDGE]] ]
+; CHECK-NEXT:    [[DOTPRE3]] = phi i32 [ [[DOTPRE]], [[FOR_END54SPLIT]] ], [ [[DOTPRE2]], [[IF_END_FOR_END54_CRIT_EDGE]] ]
+; CHECK-NEXT:    [[TMP3]] = phi i32 [ [[DOTPRE1]], [[FOR_END54SPLIT]] ], [ [[TMP0]], [[IF_END_FOR_END54_CRIT_EDGE]] ]
+; CHECK-NEXT:    [[TMP4]] = phi i32 [ [[DOTPRE]], [[FOR_END54SPLIT]] ], [ [[TMP1]], [[IF_END_FOR_END54_CRIT_EDGE]] ]
+; CHECK-NEXT:    [[ARRAYIDX56:%.*]] = getelementptr inbounds [1 x i32], ptr @e, i64 0, i64 [[IDXPROM55_PRE_PHI]]
+; CHECK-NEXT:    tail call void null(i32 noundef signext [[TMP3]])
+; CHECK-NEXT:    br label [[WHILE_BODY]]
+;
+entry:
+  br label %while.body
+
+while.body:                                       ; preds = %for.end54, %entry
+  br label %for.body3
+
+for.body3:                                        ; preds = %if.end49, %while.body
+  br i1 false, label %if.else, label %for.cond6.preheader
+
+for.cond6.preheader:                              ; preds = %for.body3
+  br label %if.end49
+
+if.else:                                          ; preds = %for.body3
+  %0 = load ptr, ptr null, align 8
+  store volatile i32 0, ptr %0, align 4
+  br i1 false, label %if.end, label %for.end54
+
+if.end:                                           ; preds = %if.else
+  br i1 false, label %if.end49, label %for.end54
+
+if.end49:                                         ; preds = %if.end, %for.cond6.preheader
+  br i1 true, label %for.body3, label %for.end54
+
+for.end54:                                        ; preds = %if.end49, %if.end, %if.else
+  %1 = load i32, ptr @g, align 4
+  %idxprom55 = sext i32 %1 to i64
+  %arrayidx56 = getelementptr inbounds [1 x i32], ptr @e, i64 0, i64 %idxprom55
+  %2 = load i32, ptr %arrayidx56, align 4
+  tail call void null(i32 noundef signext %2)
+  br label %while.body
+}
+