From 701a4aef7fa0ece4dc1fdbc88b981820564cb4e4 Mon Sep 17 00:00:00 2001
From: Dan Gohman <gohman@apple.com>
Date: Thu, 8 Apr 2010 05:57:57 +0000
Subject: [PATCH] When expanding expressions which are using post-inc mode for
 multiple loops, ensure that the expansion is dominated by the increments of
 those loops.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@100748 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/Scalar/LoopStrengthReduce.cpp | 16 ++++++++++++
 test/CodeGen/X86/multiple-loop-post-inc.ll   | 27 ++++++++++++++++++++
 2 files changed, 43 insertions(+)

diff --git a/lib/Transforms/Scalar/LoopStrengthReduce.cpp b/lib/Transforms/Scalar/LoopStrengthReduce.cpp
index 631092b3260..6eaa93d2aa0 100644
--- a/lib/Transforms/Scalar/LoopStrengthReduce.cpp
+++ b/lib/Transforms/Scalar/LoopStrengthReduce.cpp
@@ -2820,6 +2820,22 @@ Value *LSRInstance::Expand(const LSRFixup &LF,
     else
       Inputs.push_back(IVIncInsertPos);
   }
+  // The expansion must also be dominated by the increment positions of any
+  // loops it for which it is using post-inc mode.
+  for (PostIncLoopSet::const_iterator I = LF.PostIncLoops.begin(),
+       E = LF.PostIncLoops.end(); I != E; ++I) {
+    const Loop *PIL = *I;
+    if (PIL == L) continue;
+
+    SmallVector<BasicBlock *, 4> ExitingBlocks;
+    PIL->getExitingBlocks(ExitingBlocks);
+    if (!ExitingBlocks.empty()) {
+      BasicBlock *BB = ExitingBlocks[0];
+      for (unsigned i = 1, e = ExitingBlocks.size(); i != e; ++i)
+        BB = DT.findNearestCommonDominator(BB, ExitingBlocks[i]);
+      Inputs.push_back(BB->getTerminator());
+    }
+  }
 
   // Then, climb up the immediate dominator tree as far as we can go while
   // still being dominated by the input positions.
diff --git a/test/CodeGen/X86/multiple-loop-post-inc.ll b/test/CodeGen/X86/multiple-loop-post-inc.ll
index 5feab18579d..51a06112aad 100644
--- a/test/CodeGen/X86/multiple-loop-post-inc.ll
+++ b/test/CodeGen/X86/multiple-loop-post-inc.ll
@@ -275,3 +275,30 @@ bb14:                                             ; preds = %bb12, %bb11
 return:                                           ; preds = %entry
   ret void
 }
+
+; Codegen shouldn't crash on this testcase.
+
+define void @bar(i32 %a, i32 %b) nounwind {
+entry:                           ; preds = %bb1, %entry, %for.end204
+  br label %outer
+
+outer:                                     ; preds = %bb1, %entry
+  %i6 = phi i32 [ %storemerge171, %bb1 ], [ %a, %entry ] ; <i32> [#uses=2]
+  %storemerge171 = add i32 %i6, 1      ; <i32> [#uses=1]
+  br label %inner
+
+inner:                                       ; preds = %bb0, %if.end275
+  %i8 = phi i32 [ %a, %outer ], [ %indvar.next159, %bb0 ] ; <i32> [#uses=2]
+  %t338 = load i32* undef                     ; <i32> [#uses=1]
+  %t191 = mul i32 %i8, %t338        ; <i32> [#uses=1]
+  %t179 = add i32 %i6, %t191        ; <i32> [#uses=1]
+  br label %bb0
+
+bb0:                                     ; preds = %for.body332
+  %indvar.next159 = add i32 %i8, 1     ; <i32> [#uses=1]
+  br i1 undef, label %bb1, label %inner
+
+bb1:                                     ; preds = %bb0, %outer
+  %midx.4 = phi i32 [ %t179, %bb0 ] ; <i32> [#uses=0]
+  br label %outer
+}