From: Stuart Hastings <stuart@apple.com>
Date: Sat, 14 May 2011 05:55:10 +0000 (+0000)
Subject: Avoid combining GEPs that might overflow at runtime.
X-Git-Url: http://plrg.eecs.uci.edu/git/?p=oota-llvm.git;a=commitdiff_plain;h=67f071e69795dca1151cdb8d57d222b6f041d748

Avoid combining GEPs that might overflow at runtime.
rdar://problem/9267970

Patch by Julien Lerouge!


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@131339 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Transforms/InstCombine/InstCombineCompares.cpp b/lib/Transforms/InstCombine/InstCombineCompares.cpp
index b6963c54999..ede659b0111 100644
--- a/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -634,6 +634,7 @@ Instruction *InstCombiner::FoldGEPICmp(GEPOperator *GEPLHS, Value *RHS,
     if (AllZeros)
       return FoldGEPICmp(GEPLHS, GEPRHS->getOperand(0), Cond, I);
 
+    bool GEPsInBounds = GEPLHS->isInBounds() && GEPRHS->isInBounds();
     if (GEPLHS->getNumOperands() == GEPRHS->getNumOperands()) {
       // If the GEPs only differ by one index, compare it.
       unsigned NumDifferences = 0;  // Keep track of # differences.
@@ -656,7 +657,7 @@ Instruction *InstCombiner::FoldGEPICmp(GEPOperator *GEPLHS, Value *RHS,
                                ConstantInt::get(Type::getInt1Ty(I.getContext()),
                                              ICmpInst::isTrueWhenEqual(Cond)));
 
-      else if (NumDifferences == 1) {
+      else if (NumDifferences == 1 && GEPsInBounds) {
         Value *LHSV = GEPLHS->getOperand(DiffOperand);
         Value *RHSV = GEPRHS->getOperand(DiffOperand);
         // Make sure we do a signed comparison here.
@@ -667,6 +668,7 @@ Instruction *InstCombiner::FoldGEPICmp(GEPOperator *GEPLHS, Value *RHS,
     // Only lower this if the icmp is the only user of the GEP or if we expect
     // the result to fold to a constant!
     if (TD &&
+        GEPsInBounds &&
         (isa<ConstantExpr>(GEPLHS) || GEPLHS->hasOneUse()) &&
         (isa<ConstantExpr>(GEPRHS) || GEPRHS->hasOneUse())) {
       // ((gep Ptr, OFFSET1) cmp (gep Ptr, OFFSET2)  --->  (OFFSET1 cmp OFFSET2)
diff --git a/test/Transforms/InstCombine/2011-05-13-InBoundsGEP.ll b/test/Transforms/InstCombine/2011-05-13-InBoundsGEP.ll
new file mode 100644
index 00000000000..d65173db8cc
--- /dev/null
+++ b/test/Transforms/InstCombine/2011-05-13-InBoundsGEP.ll
@@ -0,0 +1,19 @@
+; RUN: opt < %s -instcombine | lli
+; rdar://problem/9267970
+; ideally this test will run on a 32-bit host
+; must not discard GEPs that might overflow at runtime (aren't inbounds)
+
+define i32 @main(i32 %argc) {
+entry:
+    %tmp1 = add i32 %argc, -2
+    %tmp2 = add i32 %argc, 1879048192
+    %p = alloca i8
+    %p1 = getelementptr i8* %p, i32 %tmp1
+    %p2 = getelementptr i8* %p, i32 %tmp2
+    %cmp = icmp ult i8* %p1, %p2
+    br i1 %cmp, label %bbtrue, label %bbfalse
+bbtrue:          ; preds = %entry
+    ret i32 -1
+bbfalse:         ; preds = %entry
+    ret i32 0
+}