Fix for incorrect address sinking in the presence of potential overflows.

In some cases it is possible for CGP to attempt to reuse a base address from
another basic block. In those cases we have to be sure that all the address
math was either done at the same bit width, or that none of it overflowed
before it was extended.

Patch by Louis Gerbarg <lgg@apple.com>

rdar://16307442

llvm-svn: 204833

1 files changed, 8 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/CodeGenPrepare.cpp b/llvm/lib/CodeGen/CodeGenPrepare.cpp
index 428d8af359e..a3961e80031 100644
--- a/llvm/lib/CodeGen/CodeGenPrepare.cpp
+++ b/llvm/lib/CodeGen/CodeGenPrepare.cpp
@@ -2438,7 +2438,14 @@ bool CodeGenPrepare::OptimizeMemoryInst(Instruction *MemoryInst, Value *Addr,
                  cast<IntegerType>(V->getType())->getBitWidth()) {
         V = Builder.CreateTrunc(V, IntPtrTy, "sunkaddr");
       } else {
-        V = Builder.CreateSExt(V, IntPtrTy, "sunkaddr");
+        // It is only safe to sign extend the BaseReg if we know that the math
+        // required to create it did not overflow before we extend it. Since
+        // the original IR value was tossed in favor of a constant back when
+        // the AddrMode was created we need to bail out gracefully if widths
+        // do not match instead of extending it.
+        if (Result != AddrMode.BaseReg)
+            cast<Instruction>(Result)->eraseFromParent();
+        return false;
       }
       if (AddrMode.Scale != 1)
         V = Builder.CreateMul(V, ConstantInt::get(IntPtrTy, AddrMode.Scale),