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 b6963c54999c6ed514f647a254ef55b9eb3e05e4..ede659b0111012a8b4537ccb8d7a46d0678e3e48 100644 (file)
--- 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);
 
     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.
     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)));
 
                                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.
         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 &&
     // 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)
         (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 (file)
index 0000000..d65173d
--- /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
+}