From 5a57dbef33ec2d336de2a2e9da4e477a4969fe57 Mon Sep 17 00:00:00 2001
From: David Majnemer <david.majnemer@gmail.com>
Date: Tue, 4 Jun 2013 17:51:58 +0000
Subject: [PATCH] IndVarSimplify: check if loop invariant expansion can trap
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IndVarSimplify is willing to move divide instructions outside of their
loop bodies if they are invariant of the loop.  However, it may not be
safe to expand them if we do not know if they can trap.

Instead, check to see if it is not safe to expand the instruction and
skip the expansion.

This fixes PR16041.

Testcase by Rafael Ávila de Espíndola.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@183239 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/Scalar/IndVarSimplify.cpp      |  2 +-
 .../udiv-invariant-but-traps.ll               | 32 +++++++++++++++++++
 2 files changed, 33 insertions(+), 1 deletion(-)
 create mode 100644 test/Transforms/IndVarSimplify/udiv-invariant-but-traps.ll

diff --git a/lib/Transforms/Scalar/IndVarSimplify.cpp b/lib/Transforms/Scalar/IndVarSimplify.cpp
index 8e76c78f5ac..df11e92c9ed 100644
--- a/lib/Transforms/Scalar/IndVarSimplify.cpp
+++ b/lib/Transforms/Scalar/IndVarSimplify.cpp
@@ -532,7 +532,7 @@ void IndVarSimplify::RewriteLoopExitValues(Loop *L, SCEVExpander &Rewriter) {
         // and varies predictably *inside* the loop.  Evaluate the value it
         // contains when the loop exits, if possible.
         const SCEV *ExitValue = SE->getSCEVAtScope(Inst, L->getParentLoop());
-        if (!SE->isLoopInvariant(ExitValue, L))
+        if (!SE->isLoopInvariant(ExitValue, L) || !isSafeToExpand(ExitValue))
           continue;
 
         // Computing the value outside of the loop brings no benefit if :
diff --git a/test/Transforms/IndVarSimplify/udiv-invariant-but-traps.ll b/test/Transforms/IndVarSimplify/udiv-invariant-but-traps.ll
new file mode 100644
index 00000000000..b2d2629eb34
--- /dev/null
+++ b/test/Transforms/IndVarSimplify/udiv-invariant-but-traps.ll
@@ -0,0 +1,32 @@
+; RUN: opt -indvars -S < %s | FileCheck %s
+
+@b = common global i32 0, align 4
+
+define i32 @foo(i32 %x, i1 %y) {
+bb0:
+  br label %bb1
+
+bb1:
+  br i1 %y, label %bb14, label %bb8
+
+bb8:
+  %i = phi i64 [ %i.next, %bb8 ], [ 0, %bb1 ]
+  %i.next = add i64 %i, 1
+  %div = udiv i32 1, %x
+  %c = icmp eq i64 %i.next, 6
+  br i1 %c, label %bb11, label %bb8
+
+bb11:
+  br i1 %y, label %bb1, label %bb13
+
+bb13:
+  store i32 %div, i32* @b, align 4
+  br label %bb14
+
+bb14:
+  ret i32 0
+}
+
+; CHECK: @foo
+; CHECK: bb8:
+; CHECK: udiv
-- 
2.34.1