[llvm-commits] [llvm] r131339 - in /llvm/trunk: lib/Transforms/InstCombine/InstCombineCompares.cpp test/Transforms/InstCombine/2011-05-13-InBoundsGEP.ll

[Stuart Hastings]

Author: stuart
Date: Sat May 14 00:55:10 2011
New Revision: 131339

URL: http://llvm.org/viewvc/llvm-project?rev=131339&view=rev
Log:
Avoid combining GEPs that might overflow at runtime.
rdar://problem/9267970

Patch by Julien Lerouge!

Added:
    llvm/trunk/test/Transforms/InstCombine/2011-05-13-InBoundsGEP.ll
Modified:
    llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp

Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp?rev=131339&r1=131338&r2=131339&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp Sat May 14 00:55:10 2011
@@ -634,6 +634,7 @@
     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 @@
                                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 @@
     // 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)

Added: llvm/trunk/test/Transforms/InstCombine/2011-05-13-InBoundsGEP.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/2011-05-13-InBoundsGEP.ll?rev=131339&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/2011-05-13-InBoundsGEP.ll (added)
+++ llvm/trunk/test/Transforms/InstCombine/2011-05-13-InBoundsGEP.ll Sat May 14 00:55:10 2011
@@ -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
+}