From c303463dcceb6a3b15e6f4d11d7c31c1ac2ce276 Mon Sep 17 00:00:00 2001
From: Chandler Carruth <chandlerc@gmail.com>
Date: Tue, 25 Sep 2012 10:03:40 +0000
Subject: [PATCH] Fix a case where SROA did not correctly detect dead PHI or
 selects due to chains or cycles between PHIs and/or selects. Also add a
 couple of really nice test cases reduced from Kostya's reports in PR13905 and
 PR13906. Both are fixed by this patch.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@164596 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/Scalar/SROA.cpp         | 15 ++++++---
 test/Transforms/SROA/phi-and-select.ll | 45 ++++++++++++++++++++++++++
 2 files changed, 55 insertions(+), 5 deletions(-)

diff --git a/lib/Transforms/Scalar/SROA.cpp b/lib/Transforms/Scalar/SROA.cpp
index dbda6270725..b3e63ae355d 100644
--- a/lib/Transforms/Scalar/SROA.cpp
+++ b/lib/Transforms/Scalar/SROA.cpp
@@ -522,8 +522,10 @@ private:
 
   void insertUse(Instruction &I, int64_t Offset, uint64_t Size,
                  bool IsSplittable = false) {
-    // Completely skip uses which don't overlap the allocation.
-    if ((Offset >= 0 && (uint64_t)Offset >= AllocSize) ||
+    // Completely skip uses which have a zero size or don't overlap the
+    // allocation.
+    if (Size == 0 ||
+        (Offset >= 0 && (uint64_t)Offset >= AllocSize) ||
         (Offset < 0 && (uint64_t)-Offset >= Size)) {
       DEBUG(dbgs() << "WARNING: Ignoring " << Size << " byte use @" << Offset
                    << " which starts past the end of the " << AllocSize
@@ -697,6 +699,9 @@ private:
     SmallVector<std::pair<Instruction *, Instruction *>, 4> Uses;
     Visited.insert(Root);
     Uses.push_back(std::make_pair(cast<Instruction>(*U), Root));
+    // If there are no loads or stores, the access is dead. We mark that as
+    // a size zero access.
+    Size = 0;
     do {
       Instruction *I, *UsedI;
       llvm::tie(UsedI, I) = Uses.pop_back_val();
@@ -824,9 +829,9 @@ private:
   }
 
   void insertUse(Instruction &User, int64_t Offset, uint64_t Size) {
-    // If the use extends outside of the allocation, record it as a dead use
-    // for elimination later.
-    if ((uint64_t)Offset >= AllocSize ||
+    // If the use has a zero size or extends outside of the allocation, record
+    // it as a dead use for elimination later.
+    if (Size == 0 || (uint64_t)Offset >= AllocSize ||
         (Offset < 0 && (uint64_t)-Offset >= Size))
       return markAsDead(User);
 
diff --git a/test/Transforms/SROA/phi-and-select.ll b/test/Transforms/SROA/phi-and-select.ll
index ad0c55748dd..b55d917f728 100644
--- a/test/Transforms/SROA/phi-and-select.ll
+++ b/test/Transforms/SROA/phi-and-select.ll
@@ -327,3 +327,48 @@ exit:
   %load = load i32* %a
   ret i32 %load
 }
+
+define i32 @PR13905() {
+; Check a pattern where we have a chain of dead phi nodes to ensure they are
+; deleted and promotion can proceed.
+; CHECK: @PR13905
+; CHECK-NOT: alloca i32
+; CHECK: ret i32 undef
+
+entry:
+  %h = alloca i32
+  store i32 0, i32* %h
+  br i1 undef, label %loop1, label %exit
+
+loop1:
+  %phi1 = phi i32* [ null, %entry ], [ %h, %loop1 ], [ %h, %loop2 ]
+  br i1 undef, label %loop1, label %loop2
+
+loop2:
+  br i1 undef, label %loop1, label %exit
+
+exit:
+  %phi2 = phi i32* [ %phi1, %loop2 ], [ null, %entry ]
+  ret i32 undef
+}
+
+define i32 @PR13906() {
+; Another pattern which can lead to crashes due to failing to clear out dead
+; PHI nodes or select nodes. This triggers subtly differently from the above
+; cases because the PHI node is (recursively) alive, but the select is dead.
+; CHECK: @PR13906
+; CHECK-NOT: alloca
+
+entry:
+  %c = alloca i32
+  store i32 0, i32* %c
+  br label %for.cond
+
+for.cond:
+  %d.0 = phi i32* [ undef, %entry ], [ %c, %if.then ], [ %d.0, %for.cond ]
+  br i1 undef, label %if.then, label %for.cond
+
+if.then:
+  %tmpcast.d.0 = select i1 undef, i32* %c, i32* %d.0
+  br label %for.cond
+}